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Title: Histology of medicinal plants
Author: Mansfield, William
Language: English
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HISTOLOGY OF
MEDICINAL PLANTS
BY
WILLIAM MANSFIELD, A.M., PHAR.D.
Professor of Histology and Pharmacognosy, College of
Pharmacy of the City of New York
Columbia University
TOTAL ISSUE, FOUR THOUSAND
NEW YORK
JOHN WILEY & SONS, INC.
LONDON: CHAPMAN & HALL, LIMITED
Copyright, 1916, by
WILLIAM MANSFIELD
PREFACE
The object of the book is to provide a practical scientific course in
vegetable histology for the use of teachers and students in schools
and colleges.
The medicinal plants are studied in great detail because they
constitute one of the most important groups of economic plants. The
cells found in these plants are typical of the cells occurring in
the vegetable kingdom; therefore the book should prove a valuable
text-book for all students of histology.
The book contains much that is new. In Part II, which is devoted
largely to the study of cells and cell contents, is a new scientific,
yet practical, classification of cells and cell contents. The author
believes that his classification of bast fibres and hairs will clear
up much of the confusion that students have experienced when studying
these structures.
The book is replete with illustrations, all of which are from
original drawings made by the author. As most of these illustrations
are diagnostic of the plants in which they occur, they will prove
especially valuable as reference plates.
The material of the book is the outgrowth of the experience of the
author in teaching histology at the College of Pharmacy of the
City of New York, Columbia University, and of years of practical
experience gained by examining powdered drugs in the laboratory of a
large importing and exporting wholesale drug house.
The author is indebted to Ernest Leitz and Bausch & Lomb Optical
Company for the use of cuts of microscopic apparatus used in Part I
of the book.
The author also desires to express his appreciation to Professor
Walter S. Cameron, who has rendered him much valuable aid.
WILLIAM MANSFIELD.
COLUMBIA UNIVERSITY,
September, 1916.
CONTENTS
PART I
SIMPLE AND COMPOUND MICROSCOPES AND MICROSCOPIC
TECHNIC
CHAPTER I
THE SIMPLE MICROSCOPES
PAGE
Simple microscopes, forms of 4
CHAPTER II
COMPOUND MICROSCOPES
Compound microscopes, structure of 7
Compound microscopes, mechanical parts of 7
Compound microscopes, optical parts of 9
Compound microscopes, forms of 12
CHAPTER III
MICROSCOPIC MEASUREMENTS
Ocular micrometer 19
Stage micrometer 19
Mechanical stage 21
Micrometer eye-pieces 21
Camera lucida 22
Drawing apparatus 23
Microphotographic apparatus 24
CHAPTER IV
HOW TO USE THE MICROSCOPE
Illumination 26
Micro lamp 27
Care of the microscope 28
Preparation of specimens for cutting 28
Paraffin imbedding oven 30
Paraffin blocks 31
Cutting sections 31
Hand microtome 31
Machine microtomes 32
CHAPTER V
REAGENTS
Reagent set 39
Measuring cylinder 40
CHAPTER VI
HOW TO MOUNT SPECIMENS
Temporary mounts 41
Permanent mounts 41
Cover glasses 43
Glass slides 44
Forceps 45
Needles 46
Scissors 46
Turntable 46
Labeling 47
Preservation of mounted specimens 48
Slide box 48
Slide tray 48
Slide cabinet 49
PART II
TISSUES, CELLS AND CELL CONTENTS
CHAPTER I
THE CELL
Typical cell 53
Changes in a cell undergoing division 55
Origin of multicellular plants 57
CHAPTER II
THE EPIDERMIS AND PERIDERM
Leaf epidermis 59
Testa epidermis 63
Plant hairs 66
Forms of hairs 67
Papillæ 67
Unicellular hairs 69
Multicellular hairs 72
Periderm 80
Cork periderm 80
Stone cell periderm 85
Parenchyma and stone cell periderm 85
CHAPTER III
MECHANICAL TISSUES
Bast fibres 89
Crystal bearing bast fibres 90
Porous and striated bast fibres 92
Porous and non-striated bast fibres 96
Non-porous and striated bast fibres 96
Non-porous and non-striated bast fibres 96
Occurrence of bast fibres in powdered drugs 103
Wood fibres 104
Collenchyma cells 106
Stone cells 109
Endodermal cells 116
Hypodermal cells 118
CHAPTER IV
ABSORPTION TISSUE
Root hairs 121
CHAPTER V
CONDUCTING TISSUE
Vessels and tracheids 126
Annular vessels 127
Spiral vessels 127
Sclariform vessels 128
Reticulate vessels 131
Pitted vessels 131
Pitted vessels with bordered pores 131
Sieve tubes 136
Sieve plate 138
Medullary bundles, rays and cells 138
Medullary ray bundle 139
The medullary ray 139
The medullary ray cell 141
Structure of the medullary ray cells 142
Arrangement of the medullary ray cells in the medullary ray 142
Latex tubes 142
Parenchyma 144
Cortical parenchyma 147
Pith parenchyma 147
Leaf parenchyma 150
Aquatic plant parenchyma 150
Wood parenchyma 150
Phloem parenchyma 150
Palisade parenchyma 150
CHAPTER VI
AERATING TISSUE
Water pores 151
Stomata 151
Relation of stomata to the surrounding cells 154
Lenticels 157
Intercellular spaces 158
CHAPTER VII
SYNTHETIC TISSUE
Photosynthetic tissue 163
Glandular tissue 164
Glandular hairs 164
Secretion cavities 166
Schizogenous cavities 168
Lysigenous cavities 168
Schizo-lysigenous cavities 168
CHAPTER VIII
STORAGE TISSUE
Storage cells 173
Storage cavities 176
Crystal cavities 176
Mucilage cavities 176
Latex cavities 176
Oil cavity 178
Glandular hairs as storage organs 178
Storage walls 179
CHAPTER IX
CELL CONTENTS
Chlorophyll 182
Leucoplastids 183
Starch grains 183
Occurrence 184
Outline 185
Size 185
Hilum 185
Nature of hilum 188
Inulin 194
Mucilage 194
Hesperidin 196
Volatile oil 196
Tannin 196
Aleurone grains 197
Structure of aleurone grains 197
Form of aleurone grains 197
Description of aleurone grains 198
Tests for aleurone grains 198
Crystals 200
Micro-crystals 200
Raphides 200
Rosette crystals 202
Solitary crystals 205
Cystoliths 210
Forms of cystoliths 210
Tests for cystoliths 215
PART III
HISTOLOGY OF ROOTS, RHIZOMES, STEMS, BARKS,
WOODS, FLOWERS, FRUITS AND SEEDS
CHAPTER I
ROOTS AND RHIZOMES
Cross-section of pink root 219
Cross-section of ruellia root 219
Cross-section of spigelia rhizome 223
Cross-section of ruellia rhizome 226
Powdered pink root 227
Powdered ruellia root 227
CHAPTER II
STEMS
Herbaceous stems 233
Cross-section, spigelia stem 233
Ruellia stem 235
Powdered horehound 237
Powdered spurious horehound 237
Insect flower stems 241
CHAPTER III
WOODY STEMS
Buchu stem 242
Mature buchu stem 242
Powdered buchu stem 245
CHAPTER IV
BARKS
White pine bark 248
Powdered white pine bark 250
CHAPTER V
WOODS
Cross-section quassia 254
Radial-section quassia 254
Tangential-section quassia 258
CHAPTER VI
LEAVES
Klip buchu 260
Powdered klip buchu 262
Mountain laurel 264
Trailing arbutus 264
CHAPTER VII
FLOWERS
Pollen grains 270
Non-spiny-walled pollen grains 273
Spiny-walled pollen grains 273
Stigma papillæ 274
Powdered insect flowers 278
Open insect flowers 280
Powdered white daisies 282
CHAPTER VIII
FRUITS
Celery fruit 285
CHAPTER IX
SEEDS
Sweet almonds 289
CHAPTER X
ARRANGEMENT OF VASCULAR BUNDLES
Types of fibro-vascular bundles 292
Radial vascular bundles 292
Concentric vascular bundles 295
Collateral vascular bundles 295
Bi-collateral vascular bundles 298
Open collateral vascular bundles 298
INDEX
TABLE OF ILLUSTRATIONS
PAGE
FIG. 1. Tripod Magnifier 4
FIG. 2. Watchmaker’s Loupe 4
FIG. 3. Folding Magnifier 4
FIG. 4. Reading Glass 4
FIG. 5. Steinheil Aplanatic Lens 5
FIG. 6. Dissecting Microscope 5
FIG. 7. Compound Microscope of Robert Hooke 8
FIG. 8. Compound Microscope 10
FIG. 9. Abbé Condenser 11
FIG. 10. 11
FIG. 11. 11
FIG. 12. Objectives 11
FIG. 13. 12
FIG. 14. 12
FIG. 15. Eye-Pieces. 12
FIG. 16. Pharmacognostic Microscope 12
FIG. 17. Research Microscope 14
FIG. 18. Special Research Microscope 14
FIG. 19. Greenough Binocular Microscope 15
FIG. 20. Polarization Microscope 16
FIG. 21. Ocular Micrometer 19
FIG. 22. Stage Micrometer 19
FIG. 23. Micrometer Eye-Piece 20
FIG. 24. Micrometer Eye-Piece 21
FIG. 25. Mechanical Stage 22
FIG. 26. Camera Lucida 22
FIG. 27. Camera Lucida 22
FIG. 28. Drawing Apparatus 23
FIG. 29. Microphotographic Apparatus 24
FIG. 30. Micro Lamp 27
FIG. 31. Paraffin-embedding Oven 30
FIG. 32. Paraffin Blocks 31
FIG. 33. Hand Microtome 31
FIG. 34. Hand Cylinder Microtome 34
FIG. 35. Hand Table Microtome 34
FIG. 36. Base Sledge Microtome 35
FIG. 37. Minot Rotary Microtome 36
FIG. 38. Reagent Set 39
FIG. 39. Measuring Cylinder 40
FIG. 40. Staining Dish 40
FIG. 41. Round Cover Glass 44
FIG. 42. Square Cover Glass 44
FIG. 43. Rectangular Cover Glass 44
FIG. 44. Glass Slide 44
FIG. 45. Histological Forceps 45
FIG. 46. Forceps 45
FIG. 47. Sliding-pin Forceps 45
FIG. 48. Dissecting Needle 46
FIG. 49. Scissors 46
FIG. 50. Scalpels 47
FIG. 51. Turntable 47
FIG. 52. Slide Box 48
FIG. 53. Slide Tray 48
FIG. 54. Slide Cabinet 49
PLATE 1 THE ONION ROOT 56
PLATE 2 LEAF EPIDERMIS 60
PLATE 3 LEAF EPIDERMIS 61
PLATE 4 TESTA EPIDERMAL CELLS 64
PLATE 5 TESTA CELLS 65
PLATE 6 PAPILLÆ 68
PLATE 7 UNICELLULAR SOLITARY HAIRS 70
PLATE 8 CLUSTERED UNICELLULAR HAIRS 71
PLATE 9 MULTICELLULAR UNISERIATE NON-BRANCHED HAIRS 73
PLATE 10 MULTICELLULAR MULTISERIATE NON-BRANCHED HAIRS 75
PLATE 11 MULTICELLULAR UNISERIATE BRANCHED HAIRS 76
PLATE 12 NON-GLANDULAR MULTICELLULAR HAIRS 78
PLATE 13 MULTICELLULAR MULTISERIATE BRANCHED HAIRS 79
PLATE 14 MULTICELLULAR MULTISERIATE BRANCHED HAIRS 81
PLATE 15 MULTICELLULAR MULTISERIATE BRANCHED HAIRS 82
PLATE 16 PERIDERM OF CASCARA SAGRADA (_Rhamnus purshiana_,
D.C.) 84
PLATE 17 MANDRAKE RHIZOME and WHITE CINNAMON 86
PLATE 18 PERIDERM OF WHITE OAK (_Quercus alba_, L.) 87
PLATE 19 CRYSTAL-BEARING FIBRES OF BARKS 91
PLATE 20 CRYSTAL-BEARING FIBRES OF BARKS 93
PLATE 21 CRYSTAL-BEARING FIBRES OF LEAVES 94
PLATE 22 BRANCHED BAST FIBRES 95
PLATE 23 POROUS AND STRIATED BAST FIBRES 97
PLATE 24 POROUS AND NON-STRIATED BAST FIBRES 98
PLATE 25 NON-POROUS AND STRIATED BAST FIBRES 99
PLATE 26 NON-POROUS AND NON-STRIATED BAST FIBRES 101
PLATE 27 GROUPS OF BAST FIBRES 102
PLATE 28 WOOD FIBRES 105
PLATE 29 CATNIP STEM and MOTHERWORT STEM 107
PLATE 30 COLLENCHYMA CELLS 108
PLATE 31 BRANCHED STONE CELLS 110
PLATE 32 POROUS AND STRIATED STONE CELLS 113
PLATE 33 POROUS AND NON-STRIATED STONE CELLS 114
PLATE 34 CINNAMON, RUELLA ROOT, CASCARA and CINNAMON 115
PLATE 35 CROSS-SECTIONS OF ENDODERMAL CELLS OF 117
PLATE 36 LONGITUDINAL SECTIONS OF ENDODERMAL CELLS 119
PLATE 37 HYPODERMAL CELLS 120
PLATE 38 CROSS-SECTION OF SARSAPARILLA ROOT (_Smilax
officinalis_, Kunth) 123
PLATE 39 ROOT HAIRS (Fragments) 124
PLATE 40 ANNULAR AND SPIRAL VESSELS 129
PLATE 41 SPIRAL VESSELS 130
PLATE 42 SCLARIFORM VESSELS 132
PLATE 43 RETICULATE VESSELS 133
PLATE 44 PITTED VESSELS 134
PLATE 45 VESSELS 135
PLATE 46 SIEVE TUBE 137
PLATE 47 RADIAL LONGITUDINAL SECTION OF WHITE SANDALWOOD
(_Santalum album_, L.) 140
PLATE 48 KAVA-KAVA ROOT and WHITE PINE BARK 143
PLATE 49 BLACK INDIAN HEMP and BLACK INDIAN HEMP ROOT 145
PLATE 50 LATEX VESSELS 146
PLATE 51 PARENCHYMA CELLS 148
PLATE 52 GRINDELIA STEM (longitudinal) and GRINDELIA STEM
(cross-section) 149
PLATE 53 ACONITE STEM and PEPPERMINT STEM 152
PLATE 54 TYPES OF STOMA 153
PLATE 55 LEAF EPIDERMI WITH STOMA 155
PLATE 56 BELLADONNA LEAF, DEER TONGUE LEAF and WHITE PINE LEAF 156
PLATE 57 ELDER BARK 159
PLATE 58 INTERCELLULAR AIR SPACES 160
PLATE 59 IRREGULAR INTERCELLULAR AIR SPACES 161
PLATE 60 GLANDULAR HAIRS 165
PLATE 61 STALKED GLANDULAR HAIRS 167
PLATE 62 CALAMUS RHIZOME and WHITE PINE BARK 169
PLATE 63 CANELLA ALBA BARK and KLIP BUCHU LEAF 170
PLATE 64 BITTER ORANCE PEEL and WHITE PINE LEAF 171
PLATE 65 CINNAMON, CALUMBA, PARENCHYMA, SARSAPARILLA,
LEPTANDRA, QUEBRACHO, BLACKBERRY 174
PLATE 66 MUCILAGE AND RESIN 175
PLATE 67 CROSS-SECTION OF SKUNK-CABBAGE LEAF (_Symplocarpus
fœtidus_, [L.] Nutt.) 177
PLATE 68 RESERVE CELLULOSE 180
PLATE 69 RESERVE CELLULOSE 181
PLATE 70 STARCH 186
PLATE 71 STARCH 187
PLATE 72 STARCH 189
PLATE 73 STARCH 190
PLATE 74 STARCH 191
PLATE 75 STARCH GRAINS 192
PLATE 76 STARCH MASSES 193
PLATE 77 INULIN (_Inula helenium_, L.) 195
PLATE 77_a_ ALEURONE GRAINS 199
PLATE 78 MICRO-CRYSTALS 201
PLATE 79 RAPHIDES 203
PLATE 80 ROSETTE CRYSTALS 204
PLATE 81 INCLOSED ROSETTE CRYSTALS 206
PLATE 82 SOLITARY CRYSTAL 207
PLATE 83 SOLITARY CRYSTALS 208
PLATE 84 SOLITARY CRYSTALS 209
PLATE 85 SOLITARY CRYSTALS 211
PLATE 86 SOLITARY CRYSTALS 212
PLATE 87 ROSETTE CRYSTALS AND SOLITARY CRYSTALS OCCURRING IN 213
PLATE 88 CYSTOLITHS 214
PLATE 89 CROSS-SECTION OF ROOT OF SPIGELIA MARYLANDICA, L. 220
PLATE 90 RUELLIA ROOT (_Ruellia ciliosa_, Pursh.). 222
PLATE 91 CROSS-SECTION OF RHIZOME OF SPIGELIA MARYLANDICA, L. 224
PLATE 92 CROSS-SECTION OF RHIZOME OF RUELLIA CILIOSA, Pursh. 225
PLATE 93 POWDERED SPIGELIA MARYLANDICA, L. 228
PLATE 94 POWDERED RUELLIA CILIOSA, Pursh. 229
PLATE 95 CROSS-SECTION OF STEM OF SPIGELIA MARYLANDICA, L. 234
PLATE 96 CROSS-SECTION OF STEM OF RUELLIA CILIOSA, Pursh. 236
PLATE 97 POWDERED HOREHOUND (_Marrubium vulgare_, L). 238
PLATE 98 SPURIOUS HOREHOUND (_Marrubium peregrinum_, L.) 239
PLATE 99 POWDERED INSECT FLOWER STEMS (_Chrysanthemum
cinerariifolium_, [Trev.], Vis.) 240
PLATE 100 CROSS-SECTION OF BUCHU STEMS (_Barosma betulina_
[Berg.], Barth, and Wendl.) 243
PLATE 101 BUCHU STEM and LEPTANDRA RHIZOME 244
PLATE 102 POWDERED BUCHU STEMS (_Barosma betulina_ [Berg.],
Barth. and Wendl.). 246
PLATE 103 CROSS-SECTION OF UNROSSED WHITE PINE BARK (_Pinus
strobus_, L.) 249
PLATE 104 POWDERED WHITE PINE BARK (_Pinus strobus_, L.) 251
PLATE 105 CROSS-SECTION OF QUASSIA WOOD (_Picræna excelsa_
[Sw.], Lindl.) 255
PLATE 106 TANGENTIAL SECTION OF QUASSIA WOOD (_Picræna
excelsa_ [Sw.], Lindl.) 256
PLATE 107 RADIAL SECTION OF QUASSIA WOOD (_Picræna excelsa_
[Sw.], Lindl.) 257
PLATE 108 CROSS-SECTION OF KLIP BUCHU JUST OVER THE VEIN 261
PLATE 109 POWDERED KLIP BUCHU 263
PLATE 110 CROSS-SECTION MOUNTAIN LAUREL (_Kalmia latifolia_,
L.) 265
PLATE 111 CROSS-SECTION TRAILING ARBUTUS LEAF (_Epigæa
repens_, L.) 266
PLATE 112 POWDERED INSECT FLOWER LEAVES 268
PLATE 113 SMOOTH-WALLED POLLEN GRAINS 271
PLATE 114 SPINY WALLED POLLEN GRAINS 272
PLATE 115 PAPILLÆ 275
PLATE 116 PAPILLÆ OF STIGMAS 276
PLATE 117 PAPILLÆ OF STIGMAS 277
PLATE 118 POWDERED CLOSED INSECT FLOWER 279
PLATE 119 POWDERED OPEN INSECT FLOWER 281
PLATE 120 POWDERED WHITE DAISIES (_Chrysanthemum
leucanthemum_, L.) 283
PLATE 121 CROSS-SECTION OF CELERY FRUIT (_Apium
graveolens_, L.) 286
PLATE 121 CROSS-SECTION OF CELERY FRUIT (_Apium
graveolens_, L.) 286
PLATE 123 CROSS-SECTION SWEET ALMOND SEED 290
PLATE 124 CROSS-SECTION OF A RADIAL VASCULAR BUNDLE OF
SKUNK CABBAGE ROOT 293
PLATE 125 CROSS-SECTION OF A PHLOEM-CENTRIC BUNDLE OF
CALAMUS RHIZOME (_Acorus calamus_, L.) 294
PLATE 126 CROSS-SECTION OF A CLOSED COLLATERAL BUNDLE OF
MANDRAKE STEM (_Podophyllum peltatum_, L.) 286
PLATE 127 BI-COLLATERAL BUNDLE OF PUMPKIN STEM (_Curcurbita
pepo_, L.) 297
Part I
SIMPLE AND COMPOUND MICROSCOPES AND MICROSCOPIC TECHNIC
CHAPTER I
THE SIMPLE MICROSCOPES
The construction and use of the =simple microscope= (magnifiers)
undoubtedly date back to very early times. There is sufficient
evidence to prove that spheres of glass were used as burning spheres
and as magnifiers by people antedating the Greeks and Romans.
The simple microscopes of to-day have a very wide range of
application and a corresponding variation in structure and in
appearance.
Simple microscopes are used daily in classifying and studying crude
drugs, testing linen and other cloth, repairing watches, in reading,
and identifying insects. The more complex simple microscopes are used
in the dissection and classification of flowers.
The =watchmaker’s loupe=, the =linen tester=, the =reading glass=,
the =engraver’s lens=, and the simplest folding magnifiers consist
of a double convex lens. Such a lens produces an erect, enlarged
image of the object viewed when the lens is placed so that the object
is within its focal distance. The focal distance of a lens varies
according to the curvature of the lens. The greater the curvature,
the shorter the focal distance and the greater the magnification.
The more complicated simple microscope consists of two or more
lenses. The double and triple magnifiers consist of two and three
lenses respectively.
When an object is viewed through three lenses, the magnification is
greater than when viewed through one or two lenses, but a smaller
part of the object is magnified.
FORMS OF SIMPLE MICROSCOPES
TRIPOD MAGNIFIER
The =tripod magnifier= (Fig. 1) is a simple lens mounted on a
mechanical stand. The tripod is placed over the object and the focus
is obtained by means of a screw which raises or lowers the lens,
according to the degree it is magnified.
WATCHMAKER’S LOUPE
The =watchmaker’s loupe= (Fig. 2) is a one-lens magnifier mounted on
an ebony or metallic tapering rim, which can be placed over the eye
and held in position by frowning or contracting the eyelid.
[Illustration: FIG. 1.--Tripod Magnifier]
[Illustration: FIG. 2.--Watchmaker’s Loupe]
FOLDING MAGNIFIER
The =folding magnifier= (Fig. 3) of one or more lenses is mounted
in such a way that, when not in use, the lenses fold up like the
blade of a knife, and when so folded are effectively protected from
abrasion by the upper and lower surfaces of the folder.
[Illustration: FIG. 3.--Folding Magnifier]
[Illustration: FIG. 4.--Reading Glass]
READING GLASSES
=Reading glasses= (Fig. 4) are large simple magnifiers, often six
inches in diameter. The lens is encircled with a metal band and
provided with a handle.
[Illustration: FIG. 5.--Steinheil Aplanatic Lens]
STEINHEIL APLANATIC LENSES
=Steinheil aplanatic lenses= (Fig. 5) consist of three or four
lenses cemented together. The combination is such that the field is
large, flat, and achromatic. These lenses are suitable for field,
dissecting, and pocket use. When such lenses are placed in simple
holders, they make good dissecting microscopes.
[Illustration: FIG. 6.--Dissecting Microscope]
DISSECTING MICROSCOPE
The =dissecting microscope= (Fig. 6) consists of a Steinheil lens
and an elaborate stand, a firm base, a pillar, a rack and pinion,
a glass stage, beneath which there is a groove for holding a metal
plate with one black and one white surface. The nature of the object
under observation determines whether a plate is used. When the plate
is used and when the object is studied by reflected light it is
sometimes desirable to use the black and sometimes the white surface.
The mirror, which has a concave and a plain surface, is used to
reflect the light on the glass stage when the object is studied by
transmitted light. The dissecting microscope magnifies objects up to
twenty diameters, or twenty times their real size.
CHAPTER II
COMPOUND MICROSCOPES
The =compound microscope= has undergone wonderful changes since 1667,
the days of Robert Hooke. When we consider the crude construction
and the limitations of Robert Hooke’s microscope, we marvel at the
structural perfection and the unlimited possibilities of the modern
instrument. The advancement made in most sciences has followed the
gradual perfection of this instrument.
The illustration of Robert Hooke’s microscope (Fig. 7) will convey
to the mind more eloquently than words the crudeness of the early
microscopes, especially when it is compared with the present-day
microscopes.
STRUCTURE OF THE COMPOUND MICROSCOPE
The parts of the compound microscope (Fig. 8) may be grouped
into--first, the mechanical, and, secondly, into the optical parts.
THE MECHANICAL PARTS
1. The =foot= is the basal part, the part which supports all the
other mechanical and optical parts. The foot should be heavy enough
to balance the other parts when they are inclined. Most modern
instruments have a three-parted or tripod-shaped base.
2. The =pillar= is the vertical part of the microscope attached to
the base. The pillar is joined to the limb by a hinged joint. The
hinges make it possible to incline the microscope at any angle, thus
lowering its height. In this way, short, medium, and tall persons
can use the microscope with facility. The part of the pillar above
the hinge is called the _limb_. The limb may be either straight
or curved. The curved form is preferable, since it offers a more
suitable surface to grasp in transferring from box or shelf to the
desk, and _vice versa_.
[Illustration: FIG. 7.--Compound Microscope of Robert Hooke]
3. The =stage= is either stationary or movable, round or square, and
is attached to the limb just above the hinge. The upper surface is
made of a composition which is not easily attacked by moisture and
reagents. The centre of the stage is perforated by a circular opening.
4. The =sub-stage= is attached below the stage and is for the purpose
of holding the iris diaphragm and Abbé condenser. The raising and
lowering of the sub-stage are accomplished by a rack and pinion.
5. The =iris diaphragm=, which is held in the sub-stage below the
Abbé condenser, consists of a series of metal plates, so arranged
that the light entering the microscope may be cut off completely or
its amount regulated by moving a control pin.
6. The =fine adjustment= is located either at the side or at the top
of the limb. It consists of a fine rack and pinion, and is used in
focusing an object when the low-power objective is in position, or in
finding and focusing the object when the high-power objective is in
position.
7. The =coarse adjustment= is a rack and pinion used in raising and
lowering the body-tube and in finding the approximate focus when
either the high- or low-power objective is in position.
8. The =body-tube= is the path traveled by the rays of light entering
the objectives and leaving by the eye-piece. To the lower part of the
tube is attached the nose-piece, and resting in its upper part is the
draw-tube, which holds the eye-piece. On the outer surface of the
draw-tube there is a scale which indicates the distance it is drawn
from the body-tube.
9. The =nose-piece= may be simple, double, or triple, and it is
protected from dust by a circular piece of metal. Double and triple
nose-pieces may be revolved, and like the simple nose-piece they hold
the objectives in position.
THE OPTICAL PARTS
1. The =mirror= is a sub-stage attachment one surface of which is
plain and the other concave. The plain surface is used with an Abbé
condenser when the source of light is distant, while the concave
surface is used with instruments without an Abbé condenser when the
source of light is near at hand.
[Illustration: FIG. 8.--Compound Microscope
Eyepiece
Draw Tube
Body Tube
Coarse
Adjustment
Revolving Nosepiece for three Objectives
Fine Adjustment
Stage
Objectives
Limb
Abbi Condenser
Iris Diaphragm
Hinge for Inclining
Substage Attachment
Mirror
Pillar
Foot]
2. The =Abbé condenser= (Fig. 9) is a combination of two or more
lenses, arranged so as to concentrate the light on the specimen
placed on the stage. The condenser is located in the opening of the
stage, and its uppermost surface is circular and flat.
[Illustration: FIG. 9--Abbé Condenser]
3. =Objectives= (Figs. 10, 11, and 12). There are low, medium, and
high-power objectives. The low-power objectives have fewer and
larger lenses, and they magnify least, but they show more of the
object than do the high-power objectives. There are three chief
types of objectives: First, dry objectives; second, wet objectives,
of which there are the water-immersion objectives; and third, the
oil-immersion objectives. The dry objectives are used for most
histological and pharmacognostical work. For studying smaller objects
the water objective is sometimes desirable, but in bacteriological
work the oil-immersion objective is almost exclusively used. The
globule of water or oil, as the case may be, increases the amount of
light entering the objective, because the oil and water bend many
rays into the objective which would otherwise escape.
[Illustration: FIG. 10.]
[Illustration: FIG. 11.]
[Illustration: FIG. 12. Objectives.]
4. =Eye-pieces= (Figs. 13, 14, and 15) are of variable length, but
structurally they are somewhat similar. The eye-piece consists of a
metal tube with a blackened inner tube. In the centre of this tube
there is a small diaphragm for holding the ocular micrometer. In the
lower end of the tube a lens is fastened by means of a screw. This,
the field lens, is the larger lens of the ocular. The upper, smaller
lens is fastened in the tube by a screw, but there is a projecting
collar which rests, when in position, on the draw-tube.
[Illustration: FIG. 13.]
[Illustration: FIG. 14.]
[Illustration: FIG. 15. Eye-Pieces.]
The longer the tube the lower the magnification. For instance, a
two-inch ocular magnifies less than an inch and a half, a one-inch
less than a three-fourths of an inch, etc.
The greater the curvature of the lenses of the ocular the higher will
be the magnification and the shorter the tube-length.
FORMS OF COMPOUND MICROSCOPES
The following descriptions refer to three different models of
compound microscopes: one which is used chiefly as a pharmacognostic
microscope, one as a research microscope stand, while the third type
represents a research microscope stand of highest order, which is
used at the same time for taking microphotographs.
[Illustration: FIG. 16.--Pharmacognostic Microscope]
PHARMACOGNOSTIC MICROSCOPE
The =pharmacognostic microscope= (Fig. 16) is an instrument
which embodies only those parts which are most essential for the
examination of powdered drugs, bacteria, and urinary sediments. This
microscope is provided with a stage of the dimensions 105 × 105 mm.
This factor and the distance of 80 mm. from the optical centre to the
handle arm render it available for the examination of even very large
objects and preparations, or preparations suspended in glass dishes.
The stand is furnished with a side micrometer, a fine adjustment
having knobs on both sides, thereby permitting the manipulation of
the micrometer screw either by left or right hand. The illuminating
apparatus consists of the Abbé condenser of numerical aperture
of 1.20, to which is attached an iris diaphragm for the proper
adjustment of the light. A worm screw, mounted in connection with the
condenser, serves for the raising and lowering of the condenser, so
that the cone of illuminating pencils can be arranged in accordance
to the objective employed and to the preparation under observation.
The objectives necessary are those of the achromatic type, possessing
a focal length of 16.2 mm. and 3 mm. Oculars which render the best
results in regard to magnification in connection with the two
objectives mentioned are the Huyghenian eye-pieces II and IV so that
magnifications are obtained varying from 62 to 625. It is advisable,
however, to have the microscope equipped with a triple revolving
nose-piece for the objectives, so that provision is made for the
addition of an oil-immersion objective at any time later should the
microscope become available for bacteriological investigations.
THE RESEARCH MICROSCOPE
The =research microscope= used in research work (Fig. 17) must be
equipped more elaborately than the microscope especially designed for
the use of the pharmacognosist. While the simple form of microscope
is supplied with the small type of Abbé condenser, the research
microscope is furnished with a large illuminating apparatus of
which the iris diaphragm is mounted on a rack and pinion, allowing
displacement obliquely to the optical centre, also to increase
resolving power in the objectives when observing those objects which
cannot be revealed to the best advantage with central illumination.
Another iris is furnished above the condenser; this iris becomes
available the instant an object is to be observed without the aid
of the condenser, in which case the upper iris diaphragm allows
proper adjustment of the light. The mirror, one side plane, the
other concave, is mounted on a movable bar, along which it can be
slid--another convenience for the adjustment of the light. The
microscope stage of this stand is of the round, rotating and centring
pattern, which permits a limited motion to the object slide: The
rotation of the microscope stage furnishes another convenience in the
examination of objects in polarized light, allowing the preparation
to be rotated in order to distinguish the polarization properties of
the objects under observation.
[Illustration: FIG. 17.--Research Microscope]
[Illustration: FIG. 18.--Special Research Microscope]
SPECIAL RESEARCH MICROSCOPE
A =special research microscope= of the highest order (Fig. 18)
is supplied with an extra large body tube, which renders it of
special advantage for micro-photography. Otherwise in its mechanical
equipment it resembles very closely the medium-sized research
microscope stand, with the exception that the stand is larger in its
design, therefore offering universal application. In regard to the
illuminating apparatus, it is advisable to mention that the one in
the large research microscope stand is furnished with a three-lens
condenser of a numerical aperture of 1.40, while the medium-sized
research stand is provided with a two-lens condenser of a numerical
aperture of 1.20. The stage of the microscope is provided with a
cross motion--the backward and forward motion of the preparation is
secured by rack and pinion, while the side motion is controlled by a
micrometric worm screw. In cases where large preparations are to be
photographed, the draw-tube with ocular and the slider in which the
draw-tubes glide are removed to allow the full aperture of wide-angle
objectives to be made use of.
[Illustration: FIG. 19.--Greenough Binocular Microscope]
BINOCULAR MICROSCOPE
The =Greenough binocular microscope=, as shown in Fig. 19, consists
of a microscope stage with two tubes mounted side by side and moving
on the same rack and pinion for the focusing adjustment. Either tube
can be used without the other. The oculars are capable of more or
less separation to suit the eyes of different observers. In each
of the drub-like mountings, near the point where the oculars are
introduced, porro-prisms have been placed, which erect the image.
This microscope gives most perfect stereoscopic images, which are
erect instead of inverted, as in the monocular compound microscopes.
The Greenough binocular microscope is especially adapted for
dissection and for studying objects of considerable thickness.
POLARIZATION MICROSCOPE
The =polarization microscope= (Fig. 20) is used chiefly for the
examination of crystals and mineral sections as well as for the
observation of organic bodies in polarized light. It can, however,
also be used for the examination of regular biological preparations.
[Illustration: FIG. 20.--Polarization Microscope]
If compared with the regular biological microscope, the polarization
microscope is found characteristic of the following points: it is
supplied with a polarization arrangement. The latter consists of a
polarizer and analyzer. The polarizer is situated in a rotating mount
beneath the condensing system. The microscope, of which the diagram
is shown, possesses a triple “Ahrens” prism of calcite. The entering
light is divided into two polarized parts, situated perpendicularly
to each other. The so-called “ordinary” rays are reflected to one
side by total reflection, which takes place on the inner cemented
surface of the triple prism, allowing the so-called “extraordinary”
rays to pass through the condenser. If the prism is adjusted to
its focal point, it is so situated that the vibration plane of the
extra-ordinary rays are in the same position as shown in the diagram
of the illustration.
The analyzer is mounted within the microscope-tube above the
objective. Situated on a sliding plate, it can be shifted into
the optical axis whenever necessary. The analyzer consists of a
polarization prism after Glan-Thompson. The polarization plane of the
active extraordinary rays is situated perpendicularly to the plane as
shown in the diagram. The polarization prisms are ordinarily crossed.
In this position the field of the microscope is darkened as long as
no substance of a double refractive index has been introduced between
the analyzer and polarizer. In rotating the polarizer up to the mark
90, the polarization prisms are mounted parallel and the field of
the microscope is lighted again. Immediately above the analyzer and
attached to the mounting of the analyzer a lens of a comparatively
long focal length has been placed in order to overcome the difference
in focus created by the introduction of the analyzer into the optical
rays.
The condensing system is mounted on a slider, and, furthermore,
can be raised and lowered along the optical centre by means of a
rack-and-pinion adjustment. If lowered sufficiently, the condensing
system can be thrown to the side to be removed from the optical
rays. The condenser consists of three lenses. The two upper lenses
are separately mounted to an arm, which permits them to be tilted to
one side in order to be removed from the optical rays. The complete
condenser is used only in connection with high-power objectives.
As far as low-power objectives are concerned, the lower condensing
lens alone is made use of, and the latter is found mounted to the
polarizer sleeve. Below the polarizer and above the lower condensing
lens an iris diaphragm is found.
The microscope table is graduated on its periphery, and, furthermore,
carries a vernier for more exact reading.
The polarization microscope is not furnished with an objective
nose-piece. Every objective, however, is supplied with an individual
centring head, which permits the objective to be attached to
an objective clutch-changer, situated at the lower end of the
microscope-tube. The centring head permits the objectives to be
perfectly centred and to remain centred even if another objective is
introduced into the objective clutch-changer.
At an angle of 45 degrees to the polarization plane of polarizer and
analyzer, a slot has been provided, which serves for the introduction
of compensators.
Between analyzer and ocular, another slot is found which permits
the Amici-Bertrand lens to be introduced into the optical axis. The
slider for the Bertrand lens is supplied with two centring screws
whereby this lens can be perfectly and easily centred. The Bertrand
lens serves the purpose of observing the back focal plane of the
microscope objective. In order to allow the Bertrand lens to be
focused, the tube can be raised and lowered for this purpose. An iris
diaphragm is mounted above the Bertrand lens.
If the Bertrand lens is shifted out of the optical axis, one can
observe the preparation placed upon the microscope stage and,
depending on its thickness or its double refraction, the interference
color of the specimen. This interference figure is called the
orthoscopic image and, accordingly, one speaks of the microscope as
being used as an “orthoscope.”
After the Bertrand lens has been introduced into the optical axis,
the interference figure is visible in the back focal plane of the
objective. Each point of this interference figure corresponds to
a certain direction of the rays of the preparation itself. This
arrangement permits observation of the change of the reflection of
light taking place in the preparation, this in accordance with the
change of the direction of the rays. This interference figure is
called the conoscopic image, and, accordingly, the microscope is used
as a “conoscope.”
Many types of polarization microscopes have been constructed; those
of a more elaborate form are used for research investigations; others
of smaller design for routine investigations.
CHAPTER III
MICROSCOPIC MEASUREMENTS
In making critical examinations of powdered drugs, it is frequently
necessary to measure the elements under observation, particularly in
the case of starches and crystals.
[Illustration: FIG. 21.--Ocular Micrometer]
OCULAR MICROMETER
Microscopic measurements are made by the =ocular micrometer= (Fig.
21). This consists of a circular piece of transparent glass on the
centre of which is etched a one- or two-millimeter scale divided into
one hundred or two hundred divisions respectively. The value of each
line is determined by standardizing with a stage micrometer.
STAGE MICROMETER
[Illustration: FIG. 22.--Stage Micrometer]
The =stage micrometer= (Fig. 22) consists of a glass slide upon which
is etched a millimeter scale divided into one hundred equal parts or
lines: each line has a value of one hundredth of a millimeter.
STANDARDIZATION OF OCULAR MICROMETER WITH LOW-POWER OBJECTIVE
Having placed the ocular micrometer in the eye-piece and the stage
micrometer on the centre of the stage, focus until the lines of the
stage micrometer are clearly seen. Then adjust the scales until the
lines of the stage micrometer are parallel with and directly under
the lines of the ocular micrometer.
Ascertain the number of lines of the stage micrometer covered by the
one hundred lines of the ocular micrometer. Then calculate the value
of each line of the ocular. This is done in the following manner:
If the one hundred lines of the ocular cover seventy-five lines
of the stage micrometer, then the one hundred lines of the ocular
micrometer are equivalent to seventy-five one-hundredths, or
three-fourths, of a millimeter. One line of the ocular micrometer
will therefore be equivalent to one-hundredth of seventy-five
one-hundredths, or .0075 part of a millimeter, and as a micron is the
unit for measuring microscopic objects, this being equivalent to one
one-thousandth of a millimeter, the value of each line of the ocular
will therefore be 7.5 microns.
[Illustration: FIG. 23.--Micrometer Eye-Piece]
With the high-power objective in place, ascertain the value of each
line of the ocular. If one hundred lines of the ocular cover only
twelve lines of the stage micrometer, then the one hundred lines of
the ocular are equivalent to twelve one-hundredths of a millimeter,
the value of one line being equivalent to one one-hundredth of twelve
one-hundredths, or twelve ten-thousandths of a millimeter, or .0012,
or 1.2_µ_.
It will therefore be seen that objects as small as a thousandth of a
millimeter can be accurately measured by the ocular micrometer.
In making microscopic measurements it is only necessary to find how
many lines of the ocular scale are covered by the object. The number
of lines multiplied by the equivalent of each line will be the size
of the object in microns, or _micromillimeters_.
[Illustration: FIG. 24.--Micrometer Eye-Piece]
MICROMETER EYE-PIECES
=Micrometer eye-pieces= (Figs. 23 and 24) may be used in making
measurements. These eye-pieces with micrometer combinations are
preferred by some workers, but the ocular micrometer will meet the
needs of the average worker.
MECHANICAL STAGES
Moving objects by hand is tiresome and unsatisfactory, first, because
of the possibility of losing sight of the object under observation,
and secondly, because the field cannot be covered so systematically
as when a mechanical stage is used for moving slides.
The =mechanical stage= (Fig. 25) is fastened to the stage by a screw.
The slide is held by two clamps. There is a rack and pinion for
moving the slide to left or right, and another rack and pinion for
moving the slide forward and backward.
[Illustration: FIG. 25. Mechanical Stage]
CAMERA LUCIDA
The =camera lucida= is an optical mechanical device for aiding the
worker in making drawings of microscopic objects. The instrument is
particularly necessary in research work where it is desirable to
reproduce an object in all its details. In fact, all reproductions
illustrating original work should be made by means of the camera
lucida or by microphotography.
[Illustration: FIG. 26.--Camera Lucida]
[Illustration: FIG. 27.--Camera Lucida]
A great many different types of camera lucidas or drawing apparatus
are obtainable, varying from simple-inexpensive to complex-expensive
forms. Figs. 26, 27, and 28 show simple and complex forms.
[Illustration: FIG. 28.--Drawing Apparatus]
MICROPHOTOGRAPHIC APPARATUS
The =microphotographic apparatus= (Fig. 29), as the name implies, is
an apparatus constructed in such a manner that it may be attached to
a microscope when we desire to photograph microscopic objects. It
consists of a metal base and a polished metal pillar for holding the
bellows, slide holder, ground-glass observation plate, and eye-piece.
In making photographs, the small end of the bellows is attached to
the ocular of the microscope, the focus adjusted, and the object or
objects photographed. More uniform results are obtained in making
such photographs if an artificial light of an unvarying candle-power
is used.
[Illustration: FIG. 29.--Microphotographic Apparatus]
There are obtainable more elaborate microphotographic apparatus than
the one figured and described, but for most workers this one will
prove highly satisfactory. It is possible, by inclining the tube of
the microscope, to make good microphotographs with an ordinary plate
camera. This is accomplished by removing the lens of the camera and
attaching the bellows to the ocular, focusing, and photographing.
CHAPTER IV
HOW TO USE THE MICROSCOPE
In beginning work with the compound microscope, place the base of the
microscope opposite your right shoulder, if you are right-handed; or
opposite your left shoulder, if you are left-handed. Incline the body
so that the ocular is on a level with your eye, if necessary; but
if not, work with the body of the microscope in an erect position.
In viewing the specimen, keep both eyes open. Use one eye for
observation and the other for sketching. In this way it will not be
necessary to remove the observation eye from the ocular unless it be
to complete the details of a sketch.
=Learn to use both eyes.= Most workers, however, accustom themselves
to using one eye; when they are sketching, they use both eyes,
although it is not necessary to do so.
=Open the iris diaphragm=, and incline the mirror so that white light
is reflected on the Abbé condenser. Place the slide on the centre
of the stage, and if the slide contains a section of a plant, move
the slide so as to place this specimen over the centre of the Abbé
condenser. Then lower the body by means of the coarse adjustment
until the low-power object, which should always be in position when
work is begun, is within one-fourth of an inch of the stage. Then
raise the body by means of the coarse adjustment until the object,
or objects, in case a powder is being examined, is seen. Open and
close the iris diaphragm, finally adjusting the opening so that the
best possible illumination is obtained for bringing out clearly
the structure of the object or objects viewed. Then regulate the
focus by moving the body up or down by turning the fine adjustment.
When studying cross-sections or large particles of powders, it is
sometimes desirable to make low-power sketches of the specimen. In
most cases, however, only sufficient time should be spent in studying
the specimen to give an idea of the size, structure, and general
arrangement or plan or structure if a section of a plant, or, if
a powder, to note its striking characters. All the finer details
of structure are best brought out with the high-power objective in
position.
In =placing the high-power objective in position=, it is first
necessary to raise the body by the coarse adjustment; then open the
iris diaphragm, and lower the body until the objective is within
about one-eighth of an inch of the slide. Now raise the tube by
the fine adjustment until the object is in focus, then gradually
close the iris diaphragm until a clear definition of the object is
obtained. Now proceed to make an accurate sketch of the object or
objects being studied.
In =using the water or oil-immersion objectives= it is first
necessary to place a drop of distilled water or oil, as the case may
be, immediately over the specimen, then lower the body by the coarse
adjustment until the lens of the objective touches the water or the
oil. Raise the tube, regulate the light by the iris diaphragm, and
proceed as if the high-power objectives were in position.
The water or oil should be removed from the objectives and from the
slide when not in use.
After the higher-powered objective has been used, the body should
be raised, and the low-power objective placed in position. If the
draw-tube has been drawn out during the examination of the object,
replace it, but be sure to hold one hand on the nose-piece so as to
prevent scratching the objective and Abbé condenser by their coming
in forceful contact. Lastly, clean the mirror with a soft piece of
linen. In returning the microscope to its case, or to the shelf,
grasp the limb, or the pillar, firmly and carry as nearly vertical as
possible in order not to dislodge the eye-piece.
ILLUMINATION
The illumination for microscopic work may be from natural or
artificial sources.
[Illustration: FIG. 30.--Micro Lamp]
It has been generally supposed that the best possible illumination
for microscopic work is diffused sunlight obtained from a northern
direction. No matter from what direction diffused sunlight is
obtained, it will be found suitable for microscopic work. In no case
should direct sunlight be used, because it will be found blinding
in its effects upon the eyes. Natural illumination--diffused
sunlight--varies so greatly during the different months of the
year, and even during different periods of the day, that individual
workers are resorting more and more to artificial illumination. The
particular advantage of such illumination is due to the fact that
its quality and intensity are uniform at all times. There are many
ways of securing such artificial illumination, no one of which has
any particular advantage over the other. Some workers use an ordinary
gas or electric light with a color screen placed in the sub-stage
below the iris diaphragm. In other cases a globe filled with a weak
solution of copper sulphate is placed in such a way between the
source of light and the microscope that the light is focused on the
mirror. Modern mechanical ingenuity has devised, however, a number of
more convenient micro lamps (Fig. 30). These lamps are a combination
of light and screen. In some forms a number of different screens come
with each lamp, so that it is possible to obtain white-, blue-, or
dark-ground illumination. The type of the screen used will be varied
according to the nature of the object studied.
CARE OF THE MICROSCOPE
If possible, the microscope should be stored in a room of the same
temperature as that in which it is to be used. In any case, avoid
storing in a room that is cooler than the place of use, because when
it is brought into a warmer room, moisture will condense on the
ocular objectives and mirrors.
Before beginning work remove all moisture, dust, etc., from the inner
and outer lenses of the ocular, the objectives, the Abbé condenser,
and the mirror by means of a piece of soft, old linen. When the work
is finished the optical parts should be thoroughly cleaned.
If reagents have been used, be sure that none has got on the
objectives or the Abbé condenser. If any reagent has got on these
parts, wash it off with water, and then dry them thoroughly with soft
linen.
The inner lenses of the eye-pieces and the under lens of the Abbé
condenser should occasionally be cleaned. The mechanical parts of the
stand should be cleaned if dust accumulates, and the movable surfaces
should be oiled occasionally. Never attempt to make new combinations
of the ocular or objective lenses, or transfer the objectives or
ocular from one microscope to another, because the lenses of any
given microscope form a perfect lens system, and this would not be
the case if they were transferred. Keep clean cloths in a dust-proof
box. Under no circumstances touch any of the optical parts with your
fingers.
PREPARATION OF SPECIMENS FOR CUTTING
Most drug plants are supplied to pharmacists in a dried condition.
It is necessary, therefore, to boil the drug in water, the time
varying from a few minutes, in the case of thin leaves and herbs, up
to a half hour if the drug is a thick root or woody stem. If a green
(undried) drug is under examination, this first step is not necessary.
If the specimen to be cut is a leaf, a flower-petal, or other thin,
flexible part of a plant, it may be placed between pieces of elder
pith or slices of carrot or potato before cutting.
SHORT PARAFFIN PROCESS
In most cases, however, more perfect sections will be obtained if the
specimens are embedded in paraffin, by the quick paraffin process,
which is easily carried out.
After boiling the specimen in water, remove the excess of moisture
from the outer surface with filter paper or wait until the water has
evaporated. Next make a mould of stiff cardboard and pour melted
paraffin (melting at 50 or 60 degrees) into the mould to a height of
about one-half inch, when the paraffin has solidified. This may be
hastened by floating it on cool or iced water instead of allowing it
to cool at room temperature.
The specimens to be cut are now placed on the paraffin, with glue, if
necessary, to hold them in position, and melted paraffin poured over
the specimens until they are covered to a depth of about one-fourth
of an inch. Cool on iced water, trim off the outer paraffin to the
desired depth, and the Specimen will be in a condition suitable for
cutting.
Good workable sections may be cut from specimens embedded by this
quick paraffin method. After a little practice the entire process
can be carried out in less than an hour. This method of preparing
specimens for cutting will meet every need of the pharmacognosist.
LONG PARAFFIN PROCESS
In order to bring out the structure of the =protoplast= (living part
of the cell), it will be necessary to begin with the living part of
the plant and to use the long paraffin method or the collodion method.
Small fragments of a leaf, stem, or root-tip are placed in
chromic-acid solution, acetic alcohol, picric acid, chromacetic
acid, alcohol, etc., depending upon the nature of the specimen under
observation. The object of placing the living specimen in such
solutions is to kill the protoplast suddenly so that the parts of the
cell will bear the same relationship to each other that they did in
the living plant, and to fix the parts so killed.
After the fixing process is complete, the specimen is freed of the
fixing agent by washing in water. From the water-bath the specimens
are transferred successively to 10, 20, 40, 60, 70, 80, 90, and
finally 100 per cent alcohol. In this 100 per cent alcohol-bath the
last traces of moisture are removed. The length of time required to
leave the specimens in the different percentages of alcohols varies
from a few minutes to twenty-four hours, depending upon the size and
the nature of the specimen.
[Illustration: FIG. 31.--Paraffin-embedding Oven]
After dehydration the specimen is placed in a clearing
agent--chloroform or xylol--both of which are suitable when embedding
in paraffin. The clearing agents replace the alcohol in the cells,
and at the same time render the tissues transparent. From the
clearing agent the specimen is placed in a weak solution of paraffin,
dissolved xylol, or chloroform. The strength of the paraffin solution
is gradually increased until it consists of pure paraffin. The
temperature of the paraffin-embedding oven (Fig. 31) should not be
much higher than the melting-point of the paraffin.
The specimen is now ready to be embedded. First make a mould of
cardboard or a lead-embedding frame (Fig. 32), melt the paraffin, and
then place the specimen in a manner that will facilitate cutting.
Remove the excess of paraffin and cut when desired.
[Illustration: FIG. 32.--Paraffin Blocks]
In using the collodion method for embedding fibrous specimens,
as wood, bark, roots, etc., the specimen is first fixed with
picric acid, washed with water, cleared in ether-alcohol, embedded
successively in two, five, and twelve per cent ether-alcohol
collodion solution, and finally embedded in a pure collodion bath.
CUTTING SECTIONS
Specimens prepared as described above may be cut with a hand
microtome or a machine microtome.
HAND MICROTOME
In cutting sections by a =hand microtome=, it is necessary to place
the specimen, embedded in paraffin or held between pieces of elder
pith, carrot, or potato, over the second joints of the fingers,
then press the first joints firmly upon the specimen with the thumb
pressed against it. If they are correctly held, the specimens will be
just above the level of the finger and the end of the thumb, and the
joint will be below the level of the finger.
[Illustration: FIG. 33.--Hand Microtome]
Hold the section cutter (Fig. 33) firmly in the hand with the flat
surface next to the specimen. While cutting the section, press your
arm firmly against your chest, and bend the wrist nearly at right
angles to the arm. Push the cutting edge of the microtome toward the
body and through the specimen in such a way as to secure as thin a
section as possible. Do not expect to obtain nice, thin sections
during the first or second trials, but continued practice will enable
one to become quite efficient in cutting sections in this manner.
When the examination of drugs is a daily occurrence, the above method
will be found highly satisfactory.
MACHINE MICROTOMES
When a number of sections are to be prepared from a given specimen,
it is desirable to cut the sections on a machine microtome,
particularly when the sections are to be prepared for the use of
students, in which case they should be as uniform as possible.
Great care should be exercised in cutting sections with a machine
microtome--first, in the selection of the type of the microtome; and
secondly, in the style of knife used in cutting.
For soft tissues embedded in paraffin or collodion, the =rotary
microtome= with vertical knife will give best results. The thickness
of the specimen is regulated by mechanical means, so that in cutting
the sections it is only necessary to turn a crank and remove the
specimens from the knife-edge, unless there is a ribbon-carrier
attachment. If the sections are being cut from a specimen embedded
by the quick paraffin method, it is best to drop the section in a
metal cup partly filled with warm water. This will cause the paraffin
to straighten out, and the specimen will uncoil. After sufficient
specimens have been cut, the cup should be placed in a boiling-water
bath until the paraffin surrounding the sections melts and floats on
the water. Before removing the specimen from the water-bath, it is
advisable to shake the glass vigorously in order to cause as many
specimens as possible to settle to the bottom of the cup. The cup
is then placed in iced water or set aside until the paraffin has
solidified. The cake-like mass is then removed from the cup, and the
sections adhering to its under surface are removed by lifting them
carefully off with the flat side of the knife and transferring them,
together with the sections at the bottom of the cup, to a wide-mouth
bottle, and covered with alcohol, glycerine, and water mixture; or if
it is desired to stain the specimens, they should be placed in a weak
alcoholic solution.
Specimens having a hard, woody texture should be cut on a =sliding
microtome= by means of a special wood knife, which is especially
tempered to cut woody substances. Woody roots, wood, or thick bark
may be cut readily on this microtome when they have been embedded by
the quick paraffin process. The knife in the sliding microtome is
placed in a horizontal position, slanting so that the knife-edge is
drawn gradually across the specimen. After cutting, the sections are
treated as described above.
The thickness of the sections is regulated by mechanical means.
After a section has been cut, the block containing the specimen is
raised by turning a thumb-screw. In this microtome the knife, as in
the rotary type, is fixed, and the block containing the specimen is
movable.
If the specimen has been infiltrated with, and embedded in, paraffin
or collodion, the treatment of the sections after cutting should be
different.
In the case of paraffin, the sections are fastened directly to the
slide, and the paraffin is dissolved by either chloroform or xylol.
The specimen is then placed in 100, 95, and 45 per cent alcohol,
and then washed in water. These sections are now stained with
water-stains, brought back through alcohol, cleared, and mounted in
Canada balsam.
If alcoholic stains are used, it will not be necessary to dehydrate
before staining, and the dehydration after staining will also be
eliminated.
Sections infiltrated with collodion are either stained directly
without removing the collodion or after removal.
FORMS OF MICROTOMES
The =hand cylinder microtome= (Fig. 34) consists of a cylindrical
body. The clamp for holding the specimen is near the top below the
cutting surface. At the lower end is attached a micrometer screw with
a divided milled head. When moved forward one division, the specimen
is raised 0.01 mm. This micrometer screw has an upward movement of
10 mm. The cutting surface consists of a cylindrical glass ring.
[Illustration: FIG. 34.--Hand Cylinder Microtome]
[Illustration: FIG. 35.--Hand Table Microtome]
The =hand table microtome= (Fig. 35) is provided with a clamp, by
which it may be attached to the edge of a table or desk. The cutting
surface consists of two separated but parallel glass benches. The
object is held by a clamp and is raised by a micrometer screw, which,
when moved through one division by turning the divided head, raises
the specimen 0.01 mm.
The =sliding microtome= has a track of 250 mm. The object is held
by a clamp and its height regulated by hand. The disk regulating
the micrometer screw is divided into one hundred parts. When this
is turned through one division, the object is raised 0.005 mm. or
5 microns, at the same time a clock-spring in contact with teeth
registers by a clicking sound. If the disk is turned through two
divisions, there will be two clicks, etc. In this way is regulated
the thickness of the sections cut. When the micrometer screw has been
turned through the one hundred divisions, it must be unscrewed, the
specimen raised, and the steps of the process repeated. The knife is
movable and is drawn across the specimen in making sections.
[Illustration: FIG. 36.--Base Sledge Microtome]
The =base sledge microtome= (Fig. 36) has a heavy iron base which
supports a sliding-way on which the object-carrier moves. The
object-carrier is mounted on a solid mass of metal, and is provided
with a clamp for holding the object. The object is raised by turning
a knob which, when turned once, raises the specimen one to twenty
microns, according to how the feeding mechanism is set.
Sections thicker than twenty microns may be obtained by turning the
knob two or more times. The knife is fixed and is supported by two
pillars, the base of which may be moved forward or backward in such a
manner that the knife can be arranged with an oblique or right-angled
cutting surface.
[Illustration: FIG. 37.--Minot Rotary Microtome]
The =Minot rotary microtome= (Fig. 37) has a fixed knife, held in
position by two pillars, and a movable object-carrier. The object is
firmly secured by a clamp, and it is raised by a micrometer screw.
The screw is attached to a wheel having five hundred teeth on its
periphery. A pawl is adjusted to the teeth in such a way that, when
moved by turning a wheel to which it is attached, specimens varying
from one to twenty-five microns in thickness may be cut, according
to the way the adjusting disk is set. When the mechanism has been
regulated and the object adjusted for cutting, it is only necessary
to turn a crank in cutting sections.
CARE OF MICROTOMES
When not in use, microtomes should be protected from dust, and all
parts liable to friction should be oiled.
Microtome knives should be honed as often as is necessary to insure
a proper cutting edge. After cutting objects, the knives should be
removed, cleaned, and oiled.
It should be kept clearly in mind that special knives are required
for cutting collodion, paraffin, and frozen and woody sections. The
cutting edges of the different knives vary considerably, as is shown
in the preceding cuts.
CHAPTER V
REAGENTS
Little attention is given in the present work to micro-chemical
reactions for the reason that their value has been much overrated in
the past. A few reagents will be found useful, however, and these few
are given, as well as their special use. They are as follows:
LIST OF REAGENTS
=Distilled Water= is used in the alcohol, glycerine, and water
mixture as a general mounting medium. It is used when warm as a test
for inulin and it is used in preparing various reagents.
=Glycerine= is used in preparing the alcohol, glycerine, and water
mixture, in testing for aleurone grains, and as a temporary mounting
medium.
=Alcohol= is used in preparing the alcohol, glycerine, and water
mixture, in testing for volatile oils.
=Acetic Acid=. Both dilute and strong solutions are used in testing
for aleurone grains, cystoliths, and crystals of calcium oxalate.
=Hydrochloric Acid= is used in connection with phloroglucin as a test
for lignin and as a test for calcium oxalate.
=Ferric Chloride Solution= is used as a test for tannin.
=Sulphuric Acid= is used as a test for calcium oxalate.
=Tincture Alkana= is used when freshly prepared by macerating the
granulated root with alcohol and filtering, as a test for resin.
=Sodium Hydroxide=. A five per cent solution is used as a test for
suberin and as a clearing agent.
=Copper Ammonia= is used as a test for cellulose.
=Ammonical Solution of Potash= is used as a test for fixed oils.
The solution is a mixture of equal parts of a saturated solution of
potassium hydroxide and stronger ammonia.
=Oil of Cloves= is used as a clearing fluid for sections preparatory
to mounting in Canada balsam.
=Canada Balsam= is used as a permanent mounting medium for dehydrated
specimens, and as a cement for ringing slides.
=Paraffin= is used for general embedding and infiltrating.
=Lugol’s Solution= is used as a test for starch and for aleurone
grains and proteid matters.
=Osmic Acid=. A two per cent solution is used as a test for fixed
oils.
=Alcohol, Glycerine, and Water Mixture= is used as a temporary
mounting medium and as a qualitative test for fixed oils.
=Chlorzinc Iodide= is used as a test for suberin, lignin, cellulose,
and starch.
=Analine Chloride= is used as a test for lignified cell walls of bast
fibres and of stone cells.
=Phloroglucin=. A one per cent alcoholic solution is used in
connection with hydrochloric acid as a test for lignin.
=Hæmatoxylin-Delifields= is used as a test for cellulose.
[Illustration: FIG. 38.--Reagent Set]
REAGENT SET
Each worker should be provided with a set of =reagent bottles=
(Fig. 38). Such a set may be selected according to the taste of the
individual, but experience has shown that a 30 c.c. bottle with a
ground-in pipette and a rubber bulb is preferable to other types. In
such forms the pipettes are readily cleaned, and the rubber bulbs can
be replaced when they become old and brittle. The entire set should
be protected from dust by keeping it in a case, the cover of which
should be closed when the set is not in use.
MEASURING CYLINDER
In order accurately to measure micro-chemical reagents, it is
necessary to have a standard 50 c.c. cylinder (Fig. 39) graduated to
c.c.’s. Such a cylinder should form a part of the reagent set.
[Illustration: FIG. 39.--Measuring Cylinder]
STAINING DISHES
[Illustration: FIG. 40.--Staining Dish]
There is a great variety of =staining dishes= (Fig. 40), but for
general histological work a glass staining dish with groves for
holding six or more slides and a glass cover is most desirable.
CHAPTER VI
HOW TO MOUNT SPECIMENS
The method of procedure in mounting specimens for study varies
according to the nature of the specimen, its preliminary treatment,
and the character of the mount to be made. As to duration, mounts are
either temporary or permanent.
TEMPORARY MOUNTS
In preparing a =temporary mount=, place the specimen in the centre
of a clean slide and add two or more drops of the temporary mounting
medium, which may be water, or a mixture of equal parts of alcohol,
glycerine, and water, or some micro-chemical reagent, as weak Lugol’s
solution, solution of chloral hydrate, etc. Cover this with a cover
glass and press down gently. Remove the excess of the mounting
medium with a piece of blotting paper. Now place the slide on the
stage and proceed to examine it. Such mounts can of course be used
only for short periods of study; and when the period of observation
is finished, the specimen should be removed and the slide washed,
or the slide washing may be deferred until a number of such slides
have accumulated. At any rate, when the mounting medium dries, the
specimen is no longer suitable for observation.
PERMANENT MOUNTS
Permanent mounts are prepared in much the same way as temporary, but
of course the mounting medium is different. The kind of permanent
mounting medium used depends upon the previous treatment of the
specimen. If the specimen has been preserved in alcohol or glycerine
and water, it is usually mounted in glycerine jelly. If the specimen
in question is a powder, it is placed in the centre of the slide and
a drop or two of glycerine, alcohol, and water mixture added, unless
the powder was already in suspension in such a mixture. Cut a small
cube of glycerine jelly and place it in the centre of the powder
mixture. Lift up the slide by means of pliers, or grasp the two
edges between the thumb and finger and hold over a small flame of an
alcohol lamp, or place on a steam-bath until the glycerine jelly has
melted. Next sterilize a dissecting needle, cool, and mix the powder
with the glycerine jelly, being careful not to lift the point of the
needle from the slide during the operation. If the mixing has been
carefully done, few or no air-bubbles will be present; but if they
are present, heat the needle, and while it is white hot touch the
bubbles with its point, and they will disappear. Now take a pair of
forceps and, after securing a clean cover glass near the edge, pass
them three times through the flame of the alcohol lamp. While holding
it in a slanting position, touch one side of the powder mixture and
slowly lower the cover glass until it comes in complete contact with
the mixture. Now press gently with the end of the needle-handle, and
set it aside to cool. When it is cool, place a neatly trimmed label
on one end of the slide, on which write the name of the specimen,
the number of the series of which it is to form a part, etc. Any
excess of glycerine jelly, which may have been pressed out from the
edges of the cover glass, should not be removed at once, but should
be allowed to remain on the slide for at least one month in order to
allow for shrinkage due to evaporation. At the end of a month remove
the glycerine jelly by first passing the blade of a knife, held in
a vertical position, the back of the knife being next to the slide,
around the edge of the cover glass. After turning the knife-blade so
that the flat side is in contact with slide, remove the jelly outside
of the cover glass. Any remaining fragments should be removed with
a piece of old linen or cotton cloth. Finally, ring the edge of the
cover glass with microscopical cement, of which there are many types
to be had. If the cleaning has been done thoroughly, there is no
better ringing cement than Canada balsam.
In mounting cross-sections, the method of procedure is similar to the
above, with the exception that the glycerine jelly is placed at the
side of the specimen and not in the centre. While melting the jelly,
incline the slide in order to allow the melted glycerine jelly to
flow gradually over the specimen, thus replacing the air contained in
the cells and intercellular spaces. Finish the mounting as directed
above, but under no conditions should you stir the glycerine jelly
with the section.
If specimens, after having been embedded in paraffin or collodion,
are cut, cleared, stained, and dehydrated, they are usually mounted
in Canada balsam. A small drop of this substance, which may be
obtained in collapsible tubes, is placed at one side of the specimen.
While inclining the slide, gently heat until the Canada balsam covers
the specimen. Secure a cover glass by the aid of pliers, pass it
through the flame three times, and lower it slowly while holding it
in an inclined position. Press gently on the cover glass with the
needle-handle, and keep in a horizontal position for twenty-four
hours, then place directly in a slide box or cabinet, since no
sealing is required.
Glycerine is sometimes used to make permanent mounts, but it is
unsatisfactory, because the cover glass is easily removed and the
specimen spoiled or lost, unless ringed--a procedure which is not
easily accomplished. If the specimen is to be mounted in glycerine,
it must first be placed in a mixture of alcohol, glycerine, and
water, and then transferred to glycerine. Lactic acid is another
permanent liquid-mounting medium, which is unsatisfactory in the same
way as glycerine, but like glycerine, there are certain special cases
where it is desirable to use it. When this is used, the slides should
be kept in a horizontal position, unless ringed.
COVER GLASSES
Great care should be used In the selection of =cover glasses=,
however, not only as regards their shape but as to their thickness.
The standard tube length of the different manufacturers makes an
allowance of a definite thickness for cover glasses. It is necessary,
therefore, to use cover glasses made by the manufacturer of the
microscope in use.
Cover glasses are either square or round. Of each there are four
different thicknesses and two different sizes. The standard
thicknesses are: The small size is designated three-fourths and the
large size seven-eighths.
[Illustration: FIG. 41.--Round Cover Glass]
[Illustration: FIG. 42.--Square Cover Glass]
[Illustration: FIG. 43.--Rectangular Cover Glass]
=Cover glasses= are circular (Fig. 41), square (Fig. 42), or
rectangular (Fig. 43) pieces of transparent glass used in
covering the specimens mounted on glass slides. A few years ago
much difficulty was experienced in obtaining uniformly thick and
transparent cover glasses, but no such difficulty is experienced
to-day. The type of cover glass used depends largely upon the
character of the specimen to be mounted. The square and rectangular
glasses are selected when a series of specimens are to be mounted,
but in mounting powdered drugs and histological specimens the round
cover glasses are preferable because they are more sightly and more
readily cleaned and rinsed.
GLASS SLIDES
[Illustration: FIG. 44.--Glass Slide]
=Glass slides= (Fig. 44) are rectangular pieces of transparent glass
used as a mounting surface for microscopic objects. The slides are
usually three inches long by one inch wide, and they should be
composed of white glass, and they should have ground and beveled
edges. Slides should be of uniform thickness, and they should not
become cloudy upon standing.
SLIDE AND COVER-GLASS FORCEPS
Slides and cover glasses should be grasped by their edges. To the
beginner this is not easy. In order to facilitate holding slides and
cover glasses during the mounting process, one may use a slide and a
cover-glass =forceps=. The slide forceps consists of wire bent and
twisted in such a way that it holds a slide firmly when attached to
its two edges.
[Illustration: FIG. 45.--Histological Forceps]
[Illustration: FIG. 46.--Forceps]
[Illustration: FIG. 47.--Sliding-pin Forceps]
There are various forms of cover-glass holders, but only two types as
far as the method of securing the cover glass is concerned. First,
there are the bacteriological and the histological forceps (Fig. 45),
which are self-closing. The two blades of such forceps must be forced
apart by pressure in securing the cover glass. The second type of
forceps is that in which the two blades are normally separated (Fig.
46), it being necessary to press the blades to either side of the
cover glass in order to secure and hold it. There is a modification
of this type of forceps which enables one to lock the blades by means
of a sliding pin (Fig. 47), after the cover glass has been secured.
It is well to accustom oneself to one type, for by so doing one may
become dexterous in its use.
NEEDLES
[Illustration: FIG. 48.--Dissecting Needle]
Two =dissecting needles= (Fig. 48) should form a part of the
histologist’s mounting set. The handles may be of any material, but
the needle should be of tempered steel and about two inches long.
SCISSORS
[Illustration: FIG. 49.--Scissors]
Almost any sort of =scissors= (Fig. 49) will do for histology work,
but a small scissors with fine pointed blades, are preferred.
Scissors are useful in trimming labels and in cutting strips of
leaves and sections of fibrous roots that are to be embedded and cut.
SCALPELS
[Illustration: FIG. 50.--Scalpels]
=Scalpels= (Fig. 50) have steel blades and ebony handles. These vary
in regard to size and quality of material. The cheaper grades are
quite as satisfactory, however, as the more expensive ones, and for
general use a medium-sized blade and handle will be found most useful.
TURNTABLE
[Illustration: FIG. 51.--Turntable]
Much time and energy may be saved by ringing slides on a =turntable=
(Fig. 51). There is a flat surface upon which to rest the hand
holding the brush with cement, and a revolving table upon which the
slide to be ringed is held by means of two clips. In ringing slides,
it is only necessary to revolve the table, and at the same time to
transfer the cement to the edge of the cover glass from the brush
held in the hand.
LABELING
There are many ways of =labeling slides=, but the best method is to
place on the label the name of the specimen, the powder number, and
the box, the tray or cabinet number. For example:
Powdered Arnica Flowers
No. 80--Box A--600.
PRESERVATION OF MOUNTED SPECIMENS
[Illustration: FIG. 52.--Slide Box]
[Illustration: FIG. 53.--Slide Tray]
Accurately mounted, labeled, and ringed slides should be filed away
for future study and reference. Such =filing= may be done in slide
boxes, in slide trays, or in cabinets. Slide boxes are to be had
of a holding capacity varying from one to one hundred slides. For
general use, slide boxes (Fig. 52) holding one hundred slides will
be found most useful. Some workers prefer trays (Fig. 53), because
of the saving of time in selecting specimens. Trays hold twenty
slides arranged in two rows. The cover of the tray is divided into
two sections so that, if desired, only one row of slides is uncovered
at a time. Slide cabinets (Fig. 54) are particularly desirable for
storing large individual collections, particularly when the slides
are used frequently for reference. Large selections of slides should
be numbered and card indexed in order to facilitate finding.
[Illustration: FIG. 54.--Slide Cabinet]
Part II
TISSUES CELLS, AND CELL CONTENTS
CHAPTER I
THE CELL
The =cell= is the unit of structure of all plants. In fact the cell
is the plant in many of the lower forms--so called unicellular
plants. All plants, then, consist of one or more cells.
While cells vary greatly in size, form, color, contents, and
function, still in certain respects their structure is identical.
TYPICAL CELL
The typical vegetable cell is composed of a living portion or
=protoplast= and an external covering, or =wall=. The protoplast
includes everything within the wall. It is made up of a number of
parts, each part performing certain functions yet harmonizing with
the work of the cell as a whole. The protoplast (protoplasm) is a
viscid substance resembling the white of an egg. The protoplast, when
unstained and unmagnified, appears structureless, but when stained
with dyes and magnified, it is found to be highly organized. The
two most striking parts of the protoplast are the =cytoplasm= and
the =nucleus=. The part of the protoplast lining the innermost part
of the wall is the =ectoplast=, which is less granular and slightly
denser than most of the =cytoplasm=. The cytoplasm is decidedly
granular in structure.
In the cytoplasm occurs one or more cavities, =vacuoles=, filled with
=cell sap=. Embedded in the cytoplasm are numerous =chromatophores=,
which vary in color in the different cells, from colorless to yellow,
to red, and to green. The =nucleus= is the seat of the vital activity
of the cell, and the seat of heredity. The whole life and activity of
the cell centre, therefore, in and about the nucleus.
The outer portion of the nucleus consists of a thin
membrane or wall. The membrane encloses numerous granular
particles--=chromatin=--which are highly susceptible to organic
stains. Among the granules are thread-like particles or =linin=. Near
the centre of the nucleus are one or more small rounded nucleoli. The
liquid portion of the nucleus, filling the membranes and surrounding
the chromatin, linin, and nucleoli, is the =nuclear sap=.
Other cell contents characteristic of certain cells are crystals,
starch, aleurone, oil, and alkaloids. The detailed discussion of
these substances will be deferred until a later chapter.
The =cell wall= which surrounds the protoplast is a product of its
activity. The structure and composition of the wall of any given cell
vary according to the ultimate function of the cell. The walls may be
thin or thick, porous or non-porous, and colored or colorless. The
composition of cell walls varies greatly. The majority of cell walls
are composed of cellulose, in other cells of linin, in others of
cutin, and in still others of suberin, etc. In the majority of cells
the walls are laid down in a series of layers one over the other by
apposition, similar to the manner of building a pile of paper from
separate sheets. The first layer is deposited over the primary wall,
formed during cell division; to this is added another layer, etc. A
modification of this manner of growth is that in which the layers are
built up one over the other, but the building is gradually done by
the deposit of minute particles of cell-wall substance over the older
deposits. Such walls are never striated, as is likely to be the case
in cell walls formed by the first method. In other cells the walls
are increased in thickness by the deposition of new wall material in
the older membrane. The cell walls will be discussed more fully when
the different tissues are studied in detail.
INDIRECT CELL DIVISION (KARYOKINESIS)
The purpose of cell division is to increase the number of cells
of a tissue, an organ, an organism, or to increase the number of
organisms, etc. Such cell divisions involve, first, an equal division
of the protoplast and, secondly, the formation of a wall between
the divided protoplasts. The first changes in structure of a cell
undergoing division occur in the nucleus.
CHANGES IN A CELL UNDERGOING DIVISION
The =linin threads= become thicker and shorter. The =chromatin
granules= increase in size and amount; the threads and chromatin
granules separate into a definite number of segments or =chromosomes=
(Plate 1, Fig. 2). The nuclear membrane becomes invested with a
fibrous protoplasmic layer which later separates and passes into
either end of the cell, there forming the =polar caps= (Plate 1, Fig.
3).
The =nuclear membrane= and the =nucleoli= disappear at about this
time. Two fibres, one from each polar cap, become attached to
opposite sides of the individual chromosomes. Other fibres from
the two polar caps unite to form the =spindle fibres=, which thus
extend from pole to pole. All these spindle fibres form the =nuclear
spindle= (Plate 1, Fig. 5).
The chromosomes now pass toward the division centre of the cell or
=equatorial plane= and form, collectively, the =equatorial plate=
(Plate 1, Fig. 5). At this point of cell division, the chromosomes
are =U=-shaped, and the curved part of the chromosomes faces the
equatorial plane. The chromosomes finally split into two equal
parts (Plate 1, Fig. 6). The actual separation of the halves of
chromosomes is brought about by the attached polar fibres, which
contract toward the polar caps (Plate 1, Fig. 7). The chromosomes are
finally drawn to the polar caps (Plate 1, Fig. 8). The chromosomes
now form a rounded mass. They then separate into linin threads
and chromatin granules. Nucleoli reappear, and nuclear sap forms.
Finally, a nuclear membrane develops. The spindle fibres, which still
extend from pole to pole, become thickened at the equatorial plane
(Plate 1, Fig. 8), and finally their edges become united to form the
=cell-plate= (Plate 1, Fig. 9), which extends across the cell, thus
completely separating the mother cell into two daughter cells. After
the formation of the cell-plate, the spindle fibres disappear. The
cell becomes modified to form the =middle lamella=, on either side of
which the daughter protoplast adds a cellulose layer. The ultimate
composition of the middle lamella and the composition and structure
of the cell wall will differ according to the function which the cell
will finally perform.
[Illustration: PLATE 1
Nine figures, showing stages in the cell-division common to the
onion root (_Allium cepa_, L.)]
ORIGIN OF MULTICELLULAR PLANTS
All multicellular plants are built up by the repeated cell division
of one original cell. If the cells formed are similar in structure
and function, they form a tissue. In multicellular plants many
different kinds of tissues will be formed as a result of cell
division, since there are many different functions to be performed by
such an organism. When several of these tissues become associated and
their functions are correlated, they form an organ. The association
of several organs in one form makes an organism. The oak-tree is an
organism. It is made up of organs known as flowers, leaves, stems,
roots, etc. Each of these organs is in turn made up of several kinds
of tissue. In some cases it is difficult to designate a single
function to an aggregation of cells (tissue). In fact, a tissue may
perform different functions at different periods of its existence
or it may perform two functions at one and the same time; as an
example, stone cells, whose primary function is mechanical, in many
cases function as storage tissue. The cells forming the tissues of
the plant, in fact, show great adaptability in regard to the function
which they perform. Nevertheless there is a predominating function
which all tissues perform, and the structure of the cells forming
such tissues is so uniform that it is possible to classify them.
The functional classification of tissues is chosen for the purpose
of demonstrating the adaptation of cell structure to cell function.
If the cells performing a similar function in the different plants
were identical in number, distribution, form, color, size, structure,
and cell contents, there would not be a science of histology upon
which the art of microscopic pharmacognosy is based. It may be said,
however, with certainty, that the cells forming certain of the
tissues of any given species of plant will differ in a recognizable
degree from cells performing a similar function in other species of
plants. Often a tissue is present in one plant but absent in another.
For example, many aquatic plants are devoid of mechanical fibrous
cells. The barks of certain plants have characteristic stone cells,
while in many other barks no stone cells occur. Many leaves have
characteristic trichomes; others are free from trichomes, etc. Yet
all cells performing a given function will structurally resemble
each other. In the present work the nucleus and other parts of the
living protoplast will not be considered, for the reason that these
parts are not in a condition suitable for study, because most drugs
come to market in a dried condition, a condition which eliminates
the possibility of studying the protoplast. The general structure of
the cells forming the different tissues will first be considered,
then their variation, as seen in different plants, and finally their
functions.
CHAPTER II
THE EPIDERMIS AND PERIDERM
The epidermis and its modifications, the hypodermis and the periderm,
form the dermal or protective outer layer or layers of the plant.
The epidermis of most leaves, stems of herbs, seeds, fruits, floral
organs, and young woody stems consists of a single layer of cells
which form an impervious outer covering, with the exception of the
stoma.
LEAF EPIDERMIS
The cells of the =epidermis= vary in size, in thickness of the side
and end walls, in form, in arrangement, in character of outgrowths,
in the nature of the surface deposits, in the character of
wall--whether smooth or rough--and in size.
In cross-sections of the leaf the character of both the side and end
walls is easily studied.
In surface sections--the view most frequently seen in powders--the
side walls are more conspicuous than the end wall (Plates 2 and 3).
This is so because the light is considerably retarded in passing
through the entire length of the side walls, while the light is
retarded only slightly in passing through the end wall. The light in
this case passes through the width (thickness) of the wall only. The
outer walls of epidermal cells are characteristic only when they are
striated, rough, pitted, colored, etc. In the majority of leaves the
outer wall of the epidermal cells is not diagnostic in powders, or in
surface sections.
The thickness of the end and side walls of epidermal cells differs
greatly in different plants.
As a rule, leaves of aquatic and shade-loving plants, as well as the
leaves of most herbs have thinner walled epidermal cells than have
the leaves of plants growing in soil under normal conditions, or than
have the leaves of shrubs and trees.
[Illustration: PLATE 2
LEAF EPIDERMIS
1. Uva-ursi (_Arctostaphylos uva-ursi_, [L.] Spring).
2. Boldus (_Peumus boldus_, Molina).
3. Catnip (_Nepeta cataria_, L.).
4. Digitalis (_Digitalis purpurea_, L.).
4-A. Origin of hair.]
[Illustration: PLATE 3
LEAF EPIDERMIS
1. Upper striated epidermis of chirata leaf (_Swertia chirata_,
[Roxb.] Ham.).
2. Green hellebore leaf (_Veratrum viride_, Ait.).
3. Boldus leaf (_Peumus boldus_, Molina).
4. Under epidermis of India senna (_Cassia angustifolia_, Vahl.).]
The widest possible range of cell-wall thickness is therefore found
in the medicinal leaves, because the medicinal leaves are collected
from aquatic plants, herbs, shrubs, trees, etc.
The outer wall is always thicker than the side walls. Even the
side walls vary in thickness in some leaves, the wall next to the
epidermis being thicker than the lower or innermost portion of the
wall. Frequently the outermost part of the side walls is unequally
thickened. This is the case in the beaded side walls characteristic
of the epidermis of the leaves of laurus, myrcia, boldus, and
capsicum seed, etc. The thickness of the side walls of the epidermal
cells of most leaves varies in the different leaves.
In most leaves there are five typical forms of arrangement of
epidermal cells: First, those over the veins which are elongated
in the direction of the length of the leaf; and, secondly, those
on other parts of the leaf which are usually several-sided and not
elongated in any one direction. If the epidermis of the leaf has
stoma, then there is a third type of arrangement of the epidermal
cells around the stoma; fourthly, the cells surrounding the base of
hairs; and fifthly, outgrowths of the epidermis, non-glandular and
glandular hairs, etc.
It should be borne in mind that in each species of plant the five
types of arrangement are characteristic for the species.
The character of the outer wall of the epidermal cells differs
greatly in different plants. In most cases the wall is smooth; senna
is an example of such leaves. In certain other leaves the wall
is rough, the roughness being in the form of striations. In some
cases the striations occur in a regular manner; belladonna leaf is
typical of such leaves. In other instances the wall is striated in
an irregular manner as shown in chirata epidermis. Very often an
epidermis is rough, but the roughness is not due to striations.
In these cases the epidermis is unevenly thickened, the thin
places appearing as slight depressions, the thick places as slight
elevations. Boldus has a rough, but not a striated surface.
=Surface deposits= are not of common occurrence in medicinal plants;
waxy deposits occur on the stem of sumac, on a species of raspberry,
on the fruit of bayberry, etc. Resinous deposits occur on the leaves
and stems of grindelia species, and on yerba santa.
In certain leaves there are two or three layers of cells beneath the
epidermis that are similar in structure to the epidermal cells. These
are called hypodermal cells, and they function in the same way as the
epidermal cells.
Hypodermal cells are very likely to occur on the margin of the leaf.
Uva-ursi leaf has a structure typical of leaves with hypodermal
marginal cells. Uva-ursi, like other leaves with hypodermal cells has
a greater number of hypodermal cells at the leaf margin than at any
other part of the leaf surface.
The cutinized walls of epidermal cells are stained red with saffranin.
TESTA EPIDERMIS
=Testa epidermal cells= form the epidermal layers of such seeds as
lobelia, henbane, capsicum, paprika, larkspur, belladonna, scopola,
etc.
In surface view the end walls are thick and wavy in outline;
frequently the line of union--middle lamella--of two cells is
indicated by a dark or light line, while in others the wall between
two cells appears as a single wall. The walls are porous or
non-porous, and the color of the wall varies from yellow to brown, to
colorless. These cells always occur in masses, composed partially of
entire and partially of broken fragments.
In lobelia seed (Plate 4, Fig. 2) the line of union of adjacent cell
walls appears as a dark line. The walls are wavy in outline, of a
yellowish-red color and not porous.
In henbane seed (Plate 4, Fig. 3) the line of union between the cells
is scarcely visible; the walls are decidedly wavy, more so than in
lobelia, and no pits are visible.
In capsicum seed (Plate 4, Fig. 1) the cells are very wavy and
decidedly porous, the line of union between the cell walls being
marked with irregular spaces and lines.
In belladonna seed (Plate 5, Fig. 1) the walls between two adjacent
cells are non-striated and non-porous, and extremely irregular in
outline.
[Illustration: PLATE 4
TESTA EPIDERMAL CELLS
1. Capsicum seed (_Capsicum frutescens_, L.).
2. Lobelia seed (_Lobelia inflata_, L.).
3. Henbane seed (_Hyoscyamus niger_, L.).]
[Illustration: PLATE 5
TESTA CELLS
1. Belladonna seed (_Atropa belladonna_, L.).
2. Star-aniseed (_Illicium verum_, Hooker).
3. Stramonium seed (_Datura stramonium_, L.).]
In star-anise seed (Plate 5, Fig. 2) the walls are irregularly
thickened and wavy in outline.
In stramonium seed (Plate 5, Fig. 3) the walls are very thick, wavy
in outline, and striated.
PLANT HAIRS (TRICHOMES)
In histological work plant hairs are of great importance, as they
offer a ready means of distinguishing and differentiating between
plants, or parts of plants, when they occur in a broken or finely
powdered condition. There is no other element in powdered drugs which
is of so great a diagnostic value as the plant hair. The same plant
will always have the same type of hair, the only noticeable variation
being in the size. In microscopical drug analysis the presence of
hairs is always noted, and in many cases the purity of the powder
can be ascertained from the hairs. Botanists seem to have given
little attention to the study of plant hairs. This accounts for the
fact that information concerning them is very meagre in botanical
literature, and, as far as the author can learn, no one has attempted
to classify them. In systematic work, plant hairs could be used to
great advantage in separating genera and even species. Hairs are,
of course, a factor now in systematic work. The lack of hairs is
indicated by the term glabrous. Their presence is indicated by such
terms as hispid, villous, etc. In certain cases the term indicates
position of the hair as ciliate when the hair is marginal. When hairs
influence the color of the leaf, such terms as cinerous and canescent
are used. In all the cases cited no mention is made of the real
nature of the hair.
In systematic work, as in pharmacognosy, we must work with dried
material, and it is only those hairs which retain their form under
such conditions which are of classification value.
Hairs are the most common outgrowths of the epidermal cells. They
are classified as glandular or non-glandular, according to their
structure and function. The glandular hairs will be considered under
synthetic tissue.
Each group is again subdivided into a number of secondary groups,
depending upon the number of cells present, their form, their
arrangement, their size, their color, the character of their walls,
whether rough or smooth, whether branched or non-branched, whether
curved, twisted, straight, or twisted and straight, whether pointed,
blunt, or forked.
FORMS OF HAIRS
PAPILLÆ
=Papillæ= are epidermal cells which are extended outward in the form
of small tubular outgrowths.
Papillæ occur on the following parts of the plant: flower-petals,
stigmas, styles, leaves, stems, seeds, and fruits. Papillæ occur on
only a few of the medicinal leaves.
The under surface of both Truxillo (Plate 6, Fig. 3) and Huanuca coca
have very small papillæ. The outermost wall of these papillæ are much
thicker than the side walls. The papillæ of klip buchu (Plate 6, Fig.
4), an adulterant of true buchu, has large thick-walled papillæ.
The velvety appearance of most flower-petals (Plate 6, Figs. 2 and
5) is due to the presence of papillæ. The papillæ of flower-petals
are very variable. In calendula flowers (Plate 6, Fig. 1) they
are small, yellowish in color, and the outer wall is marked with
parallel striations which appear as small teeth in cross-section.
The ray petal papillæ of anthemis consist of rather large, broad,
blunt papillæ with slightly striated walls. The papillæ of the ray
petals of the white daisy consist of papillæ which have medium sized,
cone-shaped papillæ with finely striated walls. The papillæ of the
flower stigma vary greatly in different flowers. In some cases two or
more types of papillæ occur, but even in these cases the papillæ are
characteristic of the species.
The papillæ differ greatly in the case of the flowers of the
compositæ, where two types of flowers are normally present--namely,
the ray flowers and the disk flowers.
In all cases observed the papillæ of the stigma of the ray flowers
are always smaller than the papillæ of the stigma of the disk
flowers. It would appear from extended observation that the papillæ
of the ray flower stigma are being gradually aborted. The papillæ of
the style are always different from the papillæ of the stigma. The
style papillæ are always smaller, and they are of a different form.
[Illustration: PLATE 6
PAPILLÆ
1. Calendula flowers (_Calendula officinalis_, L.).
2. White daisy ray flower (_Chrysanthemum leucanthemum_, L.).
3. Coca leaf (_Erythroxylon coca_, Lamarck).
4. Klip buchu.
5. Anthemis ray petal (_Anthemis nobilis_, L.).]
UNICELLULAR NON-GLANDULAR HAIRS
=True plant hairs= are tubular outgrowths of the epidermal cell, the
length of these outgrowths being several times the width of the hair.
The unicellular hairs are common to many plants. The two groups
of non-glandular unicellular hairs are, first, the solitary; and
secondly, the clustered hairs.
=Solitary unicellular hairs= occur on the leaves of chestnut, yerba
santa, lobelia, cannabis indica, the fruit of anise, and the stem of
allspice, senna, and cowage.
Chestnut hairs (Plate 7, Fig. 1) have smooth yellowish-colored walls,
and the cell cavity contains reddish-brown tannin. These hairs occur
solitary or clustered; the clustered hairs normally occur on the
leaf, but in powdering the drug, individual hairs of the cluster
become separated or solitary.
Yerba santa hairs (Plate 7, Fig. 4) are twisted, the lumen or cell
cavity is very small, and the walls, which are very thick, are
grayish-white.
Lobelia hairs (Plate 7, Fig. 5) are very large. The walls are
grayish-white, and the outer surface extends in the form of small
elevations which make the hair very rough. The hair tapers gradually
to a solid point.
Cannabis indica hairs (Plate 7, Fig. 6) are curved. The apex tapers
to a point and the base is broad, and it frequently contains deposits
of calcium carbonate. The walls are grayish-white in appearance, and
rough. The roughness increases toward the apex.
The hairs of anise (Plate 7, Fig. 7) are mostly curved; the walls are
thick, yellowish-white, and the outer surface is rough; this is due
to the numerous slight centrifugal projections of the outer wall.
Allspice stem hairs (Plate 7, Fig. 2) have smooth walls. The cell
cavity is reddish-brown. The hair is curved.
The hair of senna (Plate 7, Fig. 10) is light greenish-yellow with
rough papillose walls. The hair is usually curved and tapering, and
it does not have any characteristic cell contents.
[Illustration: PLATE 7
UNICELLULAR SOLITARY HAIRS
1. Chestnut leaf (_Castanea dentata_, [Marsh] Borkh).
2. Allspice stems (_Pimento, officinalis_, Lindl.).
3. Cowage.
4. Yerba santa (_Eriodictyon californicum_, [H. and A.] Greene).
5. Lobelia (_Lobelia inflata_, L.).
6. Cannabis indica (_Cannabis saliva_, L.).
7. Anise fruit (_Pimpinella anisum_, L.).
8. Hesperis matronalis (_Hesperis matronalis_, L.).
9. Galphimia glauca (_Galphimia glauca_, Cav.).
10. Senna (_Cassia angustifolia_, Vahl.).]
[Illustration: PLATE 8
CLUSTERED UNICELLULAR HAIRS
1. and 2. European oak (_Quercus infectoria_, Olivier).
3. Kamala (_Mallotus philippinensis_, [Lam.] [Muell.] Arg.).
4. Witch-hazel leaf (_Hamamelis virginiana_, L.).
5. Althea leaf (_Althæa officinalis_, L.).]
Cowage hairs (Plate 7, Fig. 3) are lance-shaped, and they
terminate in a sharp point. The outer wall contains numerous
recurved teeth-like projections. The cell cavity is filled with a
reddish-brown contents which are somewhat fissured.
=Clustered unicellular hairs= occur on the leaves of chestnut,
witch-hazel, althea, European oak, etc. In European oak (Plate 8,
Figs. 1 and 2) clusters of two and three hairs occur. The walls are
yellowish-white, smooth, and the tip of the hair is solid.
In kamala (Plate 8, Fig. 3) clusters of seven or more hairs occur;
the walls are yellowish, and the cell cavity is reddish-brown. In
witch-hazel leaf (Plate 8, Fig. 4) clusters of a variable number
of hairs occur. The hairs, which are of various lengths, have
yellowish-white, thick, smooth walls, and reddish cell contents.
In althea leaf (Plate 8, Fig. 5) the hairs are nearly straight and
the walls are smooth. The basal portions of the hair are strongly
pitted.
=Branched solitary unicellular hairs= occur on the leaves of hesperis
matronalis (Plate 7, Fig. 8), and on galphimia glauca (Plate 7, Fig.
9).
The hair of hesperis matronalis has smooth walls, and the two
branches grow out nearly parallel to the leaf surface.
The hair of galphimia glauca has rough walls, and the two branches
grow upward in a bifurcating manner.
MULTICELLULAR HAIRS
=Multicellular= hairs are divided into the uniseriate and the
multiseriate hairs. Both of these groups are divided into the
branched and the non-branched hairs, as follows:
1. =Uniseriate=.
(_A_) =Non-branched.=
(_B_) =Branched.=
2. =Multiseriate.=
(_A_) =Non-branched.=
(_B_) =Branched.=
=Multicellular uniseriate non-branched hairs= occur on the leaves of
digitalis, Western and Eastern skullcap, peppermint, thyme, yarrow,
arnica flowers, and sumac fruit.
[Illustration: PLATE 9
MULTICELLULAR UNISERIATE NON-BRANCHED HAIRS
1. Digitalis leaf (_Digitalis purpurea_, L.).
2. Arnica flower (_Arnica montana_, L.).
3. Western skullcap plant (_Scutellaria canescens_, Nutt.).
4. Eastern skullcap plant (_Scutellaria lateriflora_, L.).
5. Peppermint leaf (_Mentha piperita_, L.).
6. Thyme leaf (_Thymus vulgaris_, L.).
7. Yarrow flowers (_Achillea millefolium_, L.).
8. Wormwood leaf (_Artemisia absinthium_, L.).
9. Sumac fruit (_Rhus glabra_, L.).]
Digitalis hairs (Plate 9, Fig. 1) are made up of a varying number of
uniseriate-arranged cells of unequal length, frequently placed at
right angles to the cells above and below; the walls are of a whitish
color, and are rough or smooth.
Eastern skullcap (Plate 9, Fig. 4) has hairs with not more than four
cells; these hairs are curved, and the walls are whitish, sometimes
smooth, but usually rough. In Western skullcap (Plate 9, Fig. 3) the
hairs have sometimes as many as seven cells. The walls are white and
rough, and the individual cells of the hair are much larger than are
the cells of the hairs of true skullcap.
Peppermint (Plate 9, Fig. 5) has from one to eight cells. The hair is
curved, and the walls are very rough.
Thyme (Plate 9, Fig. 6) has short, thick, rough-walled trichomes, the
terminal cell usually being bent at nearly right angles to the other
cells.
Yarrow hairs (Plate 9, Fig. 7) have a variable number of cells. In
all the hairs the basal cells are short and broad, while the terminal
cell is greatly elongated.
Arnica hairs (one form, Plate 9, Fig. 2) have frequently as many as
four cells, the terminal cell being longer than the basal cells. The
walls are white and smooth.
Sumac-fruit hairs (Plate 9, Fig. 9) have spindle-shaped,
reddish-colored hairs.
=Multicellular multiseriate non-branched hairs= occur on cumin fruit
and on the tubular part of the corolla of calendula.
The hairs on cumin fruit vary considerably in size. All the hairs
are spreading at the base and blunt or rounded at the apex. The
cells forming the hair are narrow and the walls are thick. Three
differently sized hairs are shown in Plate 10, Fig. 1.
The hairs of the base of the ligulate petals of calendula (Plate 10,
Fig. 2) are biseriate. The hairs are very long and the walls are very
thin.
=Multicellular uniseriate branched hairs= occur on the leaves of
dittany of Crete, mullen, and on the calyx of lavender flowers.
The dittany of Crete (Plate 11, Fig. 3) hair is smooth-walled, and
the branches are alternate.
In mullen (Plate 11, Fig. 1) the hairs have whorled branches, the
walls are smooth, and the cell cavity usually contains air.
[Illustration: PLATE 10
MULTICELLULAR MULTISERIATE NON-BRANCHED HAIRS
1. Cumin (_Cuminum cyminum_, L.).
2. Marigold (_Calendula officinalis_, L.).]
[Illustration: PLATE 11
MULTICELLULAR UNISERIATE BRANCHED HAIRS
1. Mullen leaf (_Verbascum thapsus_, L.).
2. Lavender flowers (_Lavandula vera_, D. C.).
3. Dittany of Crete (_Origanum dictamnus_, L.).]
The lavender hairs (Plate 11, Fig. 2) have mostly opposite branches,
and the walls are rough. Thus the multicellular branched hairs may be
divided into subgroups which have alternate, opposite, whorled, or in
certain hairs irregularly arranged branches. Each class may be again
subdivided according to color, character of cell termination, etc.,
as cited at the beginning of the chapter.
Occasionally multicellular hairs assume the form of a shield (Plate
12, Fig. 1); in such cases the hair is termed peltate, as in the
non-glandular multicellular hair of shepherdia canadensis.
Hairs grow out from the surface of the epidermis in a perpendicular,
a parallel, or in an oblique direction. Hairs which grow parallel or
oblique to the surface are usually curved, and the outer curved part
of the wall is usually thicker than the inner curved wall.
The mature hairs of some plants consist of dead cells. In other
plants the cells forming the hair are living. When dried, those
hairs, which were dead before drying, contain air; while those hairs
which were living before drying, show great variation in color and in
the nature of the cell contents. The contents are either organic or
inorganic. The commonest organic constituent is dried protoplasm. In
cannabis indica are deposits of calcium carbonate.
=Multicellular multiseriate branched hairs= are the ultimate division
of the pappus of erigeron, aromatic goldenrod, arnica, grindelia,
boneset, and life-everlasting.
The hairs of erigeron (Plate 13, Figs. 1 and 2) are slender; the
walls are porous. Each hair terminates in two cells, which are
greatly extended and sharp-pointed; the branches from the basal part
of the hairs (Plate 13, Fig. 1) are of about the same length as the
apical branches.
The hairs of aromatic goldenrod (Plate 13, Figs. 3 and 4) are larger
than those of erigeron; the diameter is greater and the walls are
non-porous. The apex of the hair terminates in a group of about four
cells of unequal length, which are sharp-pointed. The branches of the
basal cells (Plate 13, Fig. 3) are similar to the branches of the
apical cells.
The hairs of arnica (Plate 14, Figs. 1 and 2) have thick, strongly
porous walls; the branches terminate in sharp points. The apex of the
hair terminates in a single cell. The basal branches (Plate 14, Fig.
2) are much longer than special branches.
[Illustration: PLATE 12
NON-GLANDULAR MULTICELLULAR HAIRS
_Shepherdia canadensis_, [L.] Nutt.]
[Illustration: PLATE 13
MULTICELLULAR MULTISERIATE BRANCHED HAIRS
1. Basal hairs of erigeron (_Erigeron canadensis_, L.).
2. Apical hairs of erigeron (_Erigeron canadensis_, L.).
3. Basal hairs of aromatic goldenrod (_Solidago odora_, Ait.).
4. Apical hairs of aromatic goldenrod (_Solidago odora_, Ait.).]
The hair of grindelia (Plate 14, Figs. 3 and 4) has very thick walls
with numerous elongated pores. The apex of the hair terminates in
a cluster of cells with short, free, sharp-pointed ends. The basal
branches (Plate 14, Fig. 4) are longer than the apical branches.
Boneset hair (Plate 15, Figs. 1 and 2) has non-porous walls. The
apex of the hair terminates in two blunt-pointed cells. The terminal
wall is thicker than the side wall. Some of the branches lower
down terminate in cells with very thick or solid points. The basal
branches (Plate 15, Fig. 1) are longer, but the cells are narrower
and more strongly tapering than are the branches of the apical part
of the hair.
Life-everlasting (Plate 15, Figs. 3 and 4) has uniformly thickened
but non-porous walls. The hair terminates in two blunt-pointed,
greatly elongated cells.
The basal branches (Plate 15, Fig. 4) are narrower, slightly
tapering, and the base of the branches frequently curve downward.
The cell cavities of these hairs are filled with air.
The walls of hairs are composed of cutin, of lignin, and of cellulose.
PERIDERM
The =periderm= is the outer protective covering of the stems
and roots of mature shrubs and trees. The periderm replaces the
epidermis. The periderm may be composed of cork cells, stone
cell-cork, or a mixture of cork, parenchyma, fibres, stone cells, etc.
CORK PERIDERM
The typical periderm is made up of =cork cells=. Cork cells vary in
appearance, according to the part of the cell viewed.
[Illustration: PLATE 14
MULTICELLULAR MULTISERIATE BRANCHED HAIRS
1. Apical hairs arnica (_Arnica montana_, L.).
2. Basal hairs arnica (_Arnica montana_, L.).
3. Apical hairs grindelia (_Grindelia squarrosa_, [Pursh] Dunal).
4. Basal hairs grindelia (_Grindelia squarrosa_, [Pursh] Dunal).]
[Illustration: PLATE 15
MULTICELLULAR MULTISERIATE BRANCHED HAIRS
1. Apical hairs boneset (_Eupatorium perfoliatum_, L.).
2. Basal hairs boneset (_Eupatorium perfoliatum_, L.).
3. Apical hairs life-everlasting (_Gnaphalium obtusifolium_, L.).
4. Basal hairs life-everlasting (_Gnaphalium obtusifolium_, L.).]
On surface view (Plate 16, Fig. A) the cork cells are angled in
outline and are made up of from four to seven side walls; five-
and six-sided cells are more common than the four-and seven-sided
cells. Surface sections of cork cells show their length and width.
These side walls usually appear nearly white, while the end wall,
particularly of the outermost cork cells, usually appears brown or
reddish-brown, or in some cases nearly black.
Cork cells on cross-section are rectangular in form, and they are
arranged in superimposed rows, the number of rows being gradually
increased as the plant grows older. Such an increase in the number of
rows of cork cells is shown in the cross-section of cascara sagrada
(Plate 16, Fig. C).
Cork cells fit together so closely that there is no intercellular
spaces between the cells. In this case two rows of cork cells occupy
no greater space than the solitary row of cork cells immediately over
and external to them. As a rule, the outermost layers of cork cells
have a narrower radial diameter than the cork cells of the underlying
layers. This is due to the fact that these outer cells are stretched
as the stem increases in diameter. This view shows the height of
cork cells, but not always the length, which will, of course, vary
according to the part of the cell cut across. In a section a few
millimeters in diameter, however, all the variations in size may be
observed. The color of the walls is nearly white.
The cavity may contain tannin or other substances. When tannin is
present, the cavity is of a brownish or brownish-red color, or it may
be nearly black. Most barks appear devoid of any colored or colorless
cell contents.
The radial section (Plate 16, Fig. B) of cork cells shows the height
of the cells and the width of the cells at the point cut across. Some
cells will be cut across their longest diameter, while others will
be cut across their shortest diameter. Cork cells are, therefore,
smaller in radial section than they are in cross-section. The color
of the walls is white, and the color and nature of the cell contents
vary for the same reasons that they vary in cross-sections.
The number of layers of cork cells occurring in cross- and
radial-sections varies according to the age of the plant, to the type
of plant, and to the conditions under which the plant is growing.
The number of layers of cork cells is not of diagnostic importance,
nor is the surface view of cork cells diagnostic except in certain
isolated cases.
[Illustration: PLATE 16
PERIDERM OF CASCARA SAGRADA (_Rhamnus purshiana_, D.C.)
_A._ 1, Outline of cork cells; 2, Line of contact of adjoining cork
cells.
_B._ Radial longitudinal section of cascara sagrada. 1, Cork cells;
2, Phellogen; 3, Forming parenchyma cells; 4, Cortical parenchyma
cells.
_C._ Cross-section of cascara sagrada. 1, Cork cells; 2, Phellogen;
3, Forming parenchyma cells; 4, Cortical parenchyma cells.]
The presence or absence of cork or epidermal tissue in powders must
always be noted. The presence of cork enables one to distinguish
Spanish from Russian licorice. In like manner, the presence of
epidermis enables one to distinguish the pharmacopœial from the
unofficial peeled calamus. The absence of epidermis in Jamaica ginger
is one of the means by which this variety is distinguished from the
other varieties of ginger, etc.
In canella alba the periderm is replaced by stone cell-cork. That is,
the cells forming the periderm are of a typical cork shape, but the
walls are lignified, unequally thickened, and the inner or thicker
walls are strongly porous, and the walls are of a yellowish color.
Stone cell-cork forms the periderm of clove bark also, but the cells
are narrower and longer, and the inner wall is not so thick or porous
as is the case in canella alba bark.
STONE CELL PERIDERM
In canella alba (Plate 17, Fig. B) cork periderm is frequently
replaced by stone cells, particularly in the older barks. These stone
cells form the periderm because they replace the cork periderm, which
fissures and scales off as the root increases in diameter.
The side and end walls of cork cells are of nearly uniform diameter.
Exceptions occur, but they are not common. In buchu stem (Plate
101, Fig. 3), the cork cells have thick outer walls, but thin sides
and inner walls. The cell cavity contains reddish-brown deposits of
tannin.
PARENCHYMA AND STONE CELL PERIDERM
As the trees and shrubs increase in diameter, cracks or fissures
occur in the periderm, or corky layer. In such cases the phellogen
cells divide and redivide in such manner as to cut off a portion of
the parenchyma cells, stone cells, and fibres of the cortex which
is inside of and below the fissure. All the parenchyma cells, etc.,
exterior to the newly formed cork cells soon lose their living-cell
contents, since their food-supply is cut off by the impervious walls
of the cork cells. In time they are forced outward by the developing
cork cells until they partially or completely fill the break in the
periderm. In white oak bark (Plate 18), as in other barks, a large
part of the periderm is composed of dead and discolored cortical
cells.
[Illustration: PLATE 17
_A._ Cross-section of Mandrake Rhizome (_Podophyllum peltatum_, L.).
1. Epidermis.
2. Phellogen.
3. Cortical parenchyma.
_B._ Stone cell periderm of white cinnamon (_Canella alba_, Murr.).]
[Illustration: PLATE 18
PERIDERM OF WHITE OAK (_Quercus alba_, L.)
1. Outer layer of cork cells. 2. Cortical parenchyma cells. 3.
Stone cells. 4. Phellogen. 5. Cortical parenchyma cells.]
ORIGIN OF CORK CELLS
The cork cells are formed by the meristimatic phellogen cells, which
originate from cortical parenchyma. These cells divide into two
cells, the outer changing into a cork cell, while the inner cell
remains meristimatic. In other instances the outer cell remains
meristimatic, while the inner cell changes into a cortical parenchyma
cell. The development of a cortical parenchyma cell from a divided
phellogen cell is shown in Plate 101, Fig. 6. Both the primary and
secondary cork cells originate from the phellogen or cork cambrium
layer. Cork cells do not contain living-cell contents; in fact, in
the majority of medicinal barks the cork cells contain only air.
The walls of typical cork cells are composed, at least in part, of
suberin, a substance which is impervious to water and gases. In
certain cases layers of cellulose, lignin, and suberin have been
identified. Suberin, however, is present in all cork cells, and in
some cases all of the walls of cork cells are composed of suberin.
Suberized cork cells are colored yellow with strong sodium hydroxide
solutions and by chlorzinciodide.
CHAPTER III
MECHANICAL TISSUES
The =mechanical tissues= of the plant form the framework around
which the plant body is built up. These tissues are constructed and
placed in such a manner in the different organs of the plant as to
meet the mechanical needs of the organ. Many underground stems and
roots which are subjected to radial pressure have the hypodermal
and endodermal cells arranged in the form of a non-compressible
cylinder. Such an arrangement is seen in sarsaparilla root (Plate
38, Fig. 4). The mechanical tissue of the stem is arranged in the
form of solid or hollow columns in order to sustain the enormous
weight of the branches. In roots the mechanical tissue is combined
in ropelike strands, thereby effectively resisting pulling stresses.
The epidermis of leaves subjected to the tearing force of the wind
has epidermal cells with greatly thickened walls, particularly at the
margin of the leaf. The epidermal cells of most seeds have very thick
and lignified cell walls, which effectively resist crushing forces.
The cells forming mechanical tissues are: bast fibres, wood
fibres, collenchyma cells, stone cells, testa epidermal cells, and
hypodermal and endodermal cells of certain plants. The walls of the
cells forming mechanical tissues are thick and lignified, with the
exception of the collenchyma cells and a few of the fibres. Lignified
cells are as resistive to pulling and other stresses as similar sized
fragments of steel. The hardness of their wall and their resistance
to crushing explain the fact that they usually retain their form in
powdered drugs and foods.
BAST FIBRES
One of the most important characters to be kept in mind in studying
bast fibres is the structure of the wall. In fact, the author’s
classification of bast fibres is based largely on wall structure.
Such a classification is logical and accurate, because it is based
upon permanent characters. Another character used in classifying bast
fibres is the nature of the cell, whether branched or non-branched.
In fact, this latter character is used to separate all bast fibres
into two fundamental groups--namely, branched bast fibres and
non-branched bast fibres. The third important character utilized in
classifying fibres is the presence or absence of crystals.
Bast fibres are classified as follows:
1. =Crystal bearing.=
2. =Non-crystal bearing.=
The crystal-bearing fibres are divided into two classes:
1. =Of leaves.=
2. =Of barks.=
The non-crystal bearing are divided into:
1. =Branched.=
2. =Non-branched.=
The branched and non-branched are divided into four classes:
1. =Non-porous and non-striated.=
2. =Porous and non-striated.=
3. =Striated and non-porous.=
4. =Porous and striated.=
CRYSTAL-BEARING BAST FIBRES
The =crystal-bearing fibres= are composed (1) of groups of fibres,
(2) of crystal cells, and (3) of crystals. In these cases the groups
of fibres are large, and they are frequently completely covered by
crystal cells, which may or may not contain a crystal. The crystals
found on the fibres from the different plants vary considerably in
size and form. As a rule, the fibres when separated are free of
crystal cells and crystals. This is so because the crystal cells
are exterior to the fibres, and in separating the fibres during
the milling process the crystal cells are broken down and removed
from the fibres. It is common, therefore, to find isolated fibres
and crystals associated with the crystal-bearing fibres. The fibres
which are crystal-bearing may be striated or porous, etc.; but owing
to the fact that the grouping of the fibres and crystals is so
characteristic, little or no attention is paid to the structure of
the individual fibres.
[Illustration: PLATE 19
CRYSTAL-BEARING FIBRES OF BARKS
1. Frangula (_Rhamnus frangula_, L.).
2. Cascara sagrada (_Rhamnus purshiana_, D.C.).
3. Spanish licorice (_Glycyrrhiza glabra_, L.).
4. Witch-hazel bark (_Hamamelis virginiana_, L.).]
=Crystal-bearing fibres= occur in the barks of frangula (Plate 19,
Fig. 1); cascara sagrada (Plate 19, Fig. 2); witch-hazel (Plate 19,
Fig. 4); in cocillana (Plate 20, Fig. 1); in white oak (Plate 20,
Fig. 2); in quebracho (Plate 20, Fig. 3); and in Spanish licorice
root (Plate 19, Fig. 3).
The crystal-bearing fibres of leaves are always associated with
vessels or tracheids and with cells with chlorophyl. The presence
or absence of crystal-bearing fibres in leaves should always be
noted. The crystal-bearing fibres of leaves are composed of fragments
of conducting cells, fibres, crystal cells, and crystals. The
crystal-bearing fibres of leaves occur in larger fragments than the
other parts of the leaf, because the fibres are more resistant to
powdering. Having observed that a leaf has crystal-bearing fibres,
in order to identify the powder it is necessary to locate one of the
other diagnostic elements of the leaf--as the papillæ of coca (Plate
21, Fig. 1), or the hair of senna (Plate 21, Fig. 3), or the vessels
in eucalyptus (Plate 21, Fig. 2).
=Branched bast fibres= occur in only a few of the medicinal plants,
notable examples being tonga root and sassafras root. Occasionally
one is found in mezereum bark.
The bast fibre of tonga root (Plate 22, Fig. 2) often has seven
branches, but four- and five-branched forms are more common. The
walls are non-porous, non-striated, and nearly white.
The bast fibre of sassafras (Plate 22, Fig. 1) has thick, non-porous,
and non-striated walls, and the branching occurs usually at one end
only of the fibre. Most of the bast fibres of sassafras root are
non-branched.
POROUS AND STRIATED BAST FIBRES
=Porous and striated= walled bast fibres occur in blackberry bark of
root, wild-cherry bark, and in cinchona bark.
The fibres of blackberry root bark (Plate 23, Fig. 1) have distinctly
porous and striated walls; the cavity, which is usually greater than
the diameter of the wall, contains starch. These fibres usually occur
as fragments.
In wild-cherry bark (Plate 23, Fig. 2) the fibre has short, thick,
unequally thickened walls, which are porous and striated. Most of the
fibres are unbroken.
[Illustration: PLATE 20
CRYSTAL-BEARING FIBRES OF BARKS
1. Cocillana (_Guarea rusbyi_, [Britton] Rusby).
2. White oak (_Quercus alba_, L.)
3. Quebracho (_Aspidosperma quebracho-blanco_, Schlechtendal).]
[Illustration: PLATE 21
CRYSTAL-BEARING FIBRES OF LEAVES
1. Coca leaf (_Erythroxylon coca_, Lam.).
2. Eucalyptus leaf (_Eucalyptus globulus_, Labill).
3. Senna leaf (_Cassia angustifolia_, Vahl.).]
[Illustration: PLATE 22
BRANCHED BAST FIBRES
1. Sassafras root bark (_Sassafras variifolium_, [Salisb.] Kuntze).
2. Tonga root.]
Yellow cinchona bark (Plate 23, Fig. 3) has very thick, prominently
striated porous-walled fibres, with either blunt or pointed ends. The
cavity is narrow, and the pores are simple or branched.
POROUS AND NON-STRIATED BAST FIBRES
=Porous and non-striated= bast fibres occur in marshmallow root and
echinacea root.
The fibres of marshmallow (Plate 24, Fig. 3) usually occur in
fragments. The walls have simple pores, and the diameter of the
cell cavity is very wide; the pores on the upper or lower wall are
circular or oval in outline (end view).
The bast fibres of echinacea root (Plate 24, Fig. 4) are seldom
broken; the walls are yellow, the pores are simple and numerous. The
edges and surface of the fibres are frequently covered with a black
intercellular substance.
NON-POROUS AND STRIATED BAST FIBRES
=Non-porous and striated= bast fibres occur in elm bark, stillingia
root, and cundurango bark. The bast fibres of elm bark (Plate 25,
Fig. 1) occur in broken, curved, or twisted fragments. The central
cavity is very small, and the walls are longitudinally striated.
In powdered stillingia root (Plate 25, Fig. 2) the bast fibres are
broken, and the wall is very thick and longitudinally striated. The
central cavity is small and usually not visible. Bast fibres of
cundurango (Plate 25, Fig. 3) are broken in the powder. The cavity
is very narrow, and the striations are arranged spirally, less
frequently transversely.
NON-POROUS AND NON-STRIATED BAST FIBRES
=Non-porous and non-striated= walled bast fibres occur in mezereum
bark, in Ceylon cinnamon, in sassafras root bark, and in soap bark.
The simplest non-porous and non-striated walled bast fibres are found
in mezereum bark (Plate 26, Fig. 4). The individual fibre is very
long. It often measures over three millimeters in length, so that in
the powder the fibre is usually broken. The wall is non-lignified,
white, non-porous, and of uniform diameter.
[Illustration: PLATE 23
POROUS AND STRIATED BAST FIBRES
1. Blackberry root (_Rubus cuneifolius_, Pursh.).
2. Wild cherry (_Prunus serotina_, Ehrh.).
3. Yellow cinchona (_Cinchona species_).]
[Illustration: PLATE 24
POROUS AND NON-STRIATED BAST FIBRES
1. Sarsaparilla root (Hypoderm), (_Smilax officinalis_, Kunth).
2. Unicorn root (Endoderm).
3. Marshmallow root (_Althæa officinalis_, L.).
4. Echinacea root (_Echinacea angustifolia_, D. C.).]
[Illustration: PLATE 25
NON-POROUS AND STRIATED BAST FIBRES
1. Elm bark (_Ulmus fulva_, Michaux).
2. Stillingia root (_Stillingia sylvatica_, L.).
3. Cundurango root bark (_Marsdenia cundurango_, [Triana] Nichols).]
In Ceylon cinnamon (Plate 26, Fig. 2) the bast fibres measure up to
.900 mm. in length, so that in powdering the bark the fibre is rarely
broken. These bast fibres, unlike the bast fibres of mezereum, have
thick, white walls and a narrow cell cavity. Both ends of the fibre
taper gradually to a long, narrow point.
In Saigon cinnamon the bast fibres are not as numerous as they are
in Ceylon cinnamon. The individual fibres are thicker than in Ceylon
cinnamon, and the walls are yellowish and rough and the ends bluntly
pointed. These fibres are rarely ever free from adhering fragments of
parenchyma tissue.
In sassafras root bark (Plate 26, Fig. 3) the fibre has one nearly
straight side--the side in contact with the other bast fibres--and
an outer side with a wavy outline, caused by the fibre’s pressing
against parenchyma cells, the point of highest elevation being the
point of the fibre’s growth into the intercellular space between two
cells. The outer part of the wall tapers gradually at either end to a
sharp point. The walls are white, thick, and non-porous.
In soap bark (Plate 26, Fig. 1) the bast fibres have thick, white,
wavy walls and a narrow cavity. One end of the cell is frequently
somewhat blunt while the opposite end is slightly tapering.
The branched stone cells of wild-cherry bark have three or more
branches. The pores are small and usually non-branched, and the
striations are very fine and difficult to see unless the iris
diaphragm is nearly closed. The central cavity is very narrow and
frequently contains brown tannin.
The branched stone cells of hemlock bark are very large; the walls
are white and distinctly porous bordering on the cell cavity, which
contains bright reddish-brown masses of tannin.
In cross-section bast fibres occur singly or isolated, as in Saigon
cinnamon (Plate 34, Fig. 1); or in groups, as in menispermum (Plate
27, Figs. 1 and 2); or in the form of continuous bands, as in buchu
stem (Plate 100, Fig. 5).
Bast fibres are seen in longitudinal view in powdered drugs. The cell
cavity shows throughout the length of the fibre. This cavity differs
greatly in different fibres. In soap bark (Plate 26, Fig. 1) there is
scarcely any cell cavity, while in mezereum bark (Plate 26, Fig. 4)
the cell cavity is very large.
[Illustration: PLATE 26
NON-POROUS AND NON-STRIATED BAST FIBRES
1. Soap bark (_Quillaja saponaria_, Molina).
2. Ceylon cinnamon bark (_Cinnamomum zeylanicum_, Nees).
3. Sassafras root bark (_Sassafras variifolium_, [Salisb.] Kuntze).
4. Mezereum bark (_Daphne mezereum_, L.).]
[Illustration: PLATE 27
GROUPS OF BAST FIBRES
1. Menispermum rhizome (_Menispermum canadensis_, L.).
2. Althea root (_Althæa officinalis_, L.) showing two groups of bast
fibres.]
The pores, which are absent in many drugs, are, when present,
either simple, as in echinacea root (Plate 24, Fig. 4), or they are
branched, as in yellow cinchona (Plate 23, Fig. 3).
In each of the above fibres the length and width of the fibre
are shown. The fibres also have pores of variable length. Such a
variation is common to most fibres with pores. That part of the wall
immediately over or below the cell cavity shows the end view or
diameter of the pore, as in the fibre of marshmallow root (Plate 24,
Fig. 3). As a rule, however, the pores show indistinctly on the upper
and lower wall.
OCCURRENCE IN POWDERED DRUGS
In powdered drugs bast fibres occur singly or in groups. The
individual fibres may be broken, as in mezereum and elm bark, or they
may be entire, as in Ceylon cinnamon and in sassafras bark (Plate 26,
Figs. 2 and 3).
The lignified walls of bast fibres are colored red by a solution of
phlorogucin and hydrochloric acid, and the walls are stained yellow
by aniline chloride.
In fact, few of the fibres found in individual plants occur in a
broken condition.
Isolated bast fibres are circular in outline. Bast fibres, when
forming part of a bundle, have angled outlines when they are
completely surrounded by other bast fibres; but when they occur on
the outer part of the bundle, and when in contact with parenchyma or
other cortical cells, they are partly angled and partly undulated in
outline.
In the bast fibres the pores are placed at right angles to the length
of the fibre. The side walls show the length of the pore (Plate 24,
Fig. 3); while the upper or lower wall shows the outline, which is
circular, and the pore, which is very minute.
Most bast fibres have no cell contents. In some cases, however,
starch occurs, as in the bast fibres of rubus.
The color of the bast fibres varies, being colorless, as in Ceylon
cinnamon; or yellowish-white, as in echinacea; or bright yellow, as
in bayberry bark.
Bast fibres retain their living-cell contents until fully developed;
then they die and function largely in a mechanical way.
The walls of bast fibres are composed of cellulose or of lignin. Most
of the bast fibres occurring in the medicinal plants give a strong
lignin reaction.
WOOD FIBRES
=Wood fibres= always occur in cross-sections associated with vessels
and wood parenchyma, from which they are distinguished by their
thicker walls, smaller diameter, and by the nature of the pores,
which are usually oblique and fewer in number than the pores in the
walls of wood parenchyma, and different in form from the pores of
vessels.
The wood fibre on cross-section (Plate 105, Fig. 4) shows an
angled outline, except in the case of the fibres bordering the
pith-parenchyma, etc., in which case they are rounded on their outer
surface, but angled at the points in contact with other fibres. The
pore of wood fibres is one of the main characteristics which enable
one to distinguish the wood fibres from bast fibres.
The pores are slanting or strongly oblique (Plate 28, Fig. 2),
and they show for their entire length on the broadest part of the
wall--_i.e._, the upper or the lower surface--while in the side wall
they are oblique; but they are not so distinct as they are on the
broad part of the wall.
Frequently the pores appear crossed when the upper and the lower wall
are in focus, because the pores are spirally arranged, and the pore
on the under wall throws a shadow across the pore on the upper wall,
or _vice versa_.
Wood fibres always occur in a broken condition (Plate 28, Fig. 1) in
powdered drugs. These broken fibres usually occur both singly and in
groups in a given powder.
The color of wood fibres varies greatly in the different medicinal
woods. Fragments of wood are usually adhering to witch-hazel, black
haw, and other medicinal barks. In each of these cases the wood
fibres are nearly colorless. In barberry bark adhering fragments of
wood and the individual fibres are greenish-yellow. The wood fibres
of santalum album are whitish-brown; of quassia, whitish-yellow; of
logwood and santalum rubrum, red.
[Illustration: PLATE 28
WOOD FIBRES
1. White sandalwood (_Santalum album_, L.).
2. Quassia wood (_Picræna excelsa_, [Swartz] Lindl.).
3. Logwood with crystals (_Hæmatoxylon campechianum_, L.).
4. Black haw root (_Viburnum prunifolium_, L.).]
Some wood fibres function as storage cells. In quassia the wood
fibres frequently contain storage starch. The wood fibres of logwood
and red saunders contain coloring substances, which are partially in
the cell cavity and partially in the cell wall.
The walls of wood are composed largely of lignin.
COLLENCHYMA CELLS
=Collenchyma cells= form the principal medicinal tissue of stems of
herbs, petioles of leaves, etc. In certain herbs the collenchyma
forms several of the outer layers of the cortex of the stem. In
motherwort, horehound, and in catnip the collenchyma cells occur
chiefly at the angles of the stem. In motherwort (Plate 29, Fig.
B) there are twelve bundles, one large bundle at each of the four
angles, and two small bundles, one on either side of the large
bundle. In catnip (Plate 29, Fig. A) there are four large masses, one
at each angle of the stem.
Collenchyma cells differ from parenchyma cells in a number of
ways: first, the cell cavity is smaller; secondly, the walls are
thicker, the greater amount of thickening being at the angles of the
cells--that is, the part of the cell wall which is opposite the usual
intercellular space of parenchyma cells, while the wall common to
two adjoining cells usually remains unthickened. In horehound stem
(Plate 30, Fig. 2) the thickening is so great at the angles that no
intercellular space remains. In the side column of motherwort stem
(Plate 30, Fig. 1) the thickening between the cells has taken place
to such an extent that the cell cavities become greatly separated and
arranged in parallel concentric rows.
The collenchyma of the outer angle of motherwort stem (Plate 30, Fig.
3) is greatly thickened at the angles. There are no intercellular
spaces between the cells, and cell cavity is usually angled in
outline instead of circular, as in the cells of horehound. In certain
plants intercellular spaces occur between the cells, and the walls
are striated instead of being non-striated, as in the stems of
horehound, motherwort, and catnip.
[Illustration: PLATE 29
_A._ Diagrammatic sketch of the cross-section of catnip stem
(_Nepeta cataria_, L.). 1. Collenchyma occurring at the four angles
of the stem.
_B._ Diagrammatic sketch of the cross-section of motherwort stem
(_Leonurus cardiaca_, L.). 1, 2, 3. Twelve masses of collenchyma
tissue occurring at the four sides of the stem.]
[Illustration: PLATE 30
COLLENCHYMA CELLS
1. Cross-section of a side column of the collenchyma of motherwort
stem (_Leonurus cardiaca_, L.).
2. Cross-section of the collenchyma of horehound stem (_Marrubium
vulgare_, L.).
3. Cross-section of the collenchyma of the outer angle of
motherwort stem.]
Collenchyma cells retain their living contents at maturity. Many
collenchyma cells, particularly of the outer layers of bark and the
collenchyma of the stems of herbs, contain chlorophyll.
The walls of collenchyma consist of cellulose.
STONE CELLS
=Stone cells=, like bast fibres, are branched or non-branched. Each
group is then separated into subgroups according to wall structure
(whether striated, or pitted and striated, etc.), thickness of wall
and of cell cavity, color of wall and of cell contents, absence of
color and of cell contents, etc.
BRANCHED STONE CELLS
=Branched stone cells= occur in a number of drugs. In witch-hazel
bark (Plate 31, Fig. 2) the walls are thick, white, and very porous.
In some cells the branches are of equal length; in others they are
unequal. In the tea-leaf (Plate 31, Fig. 1) the walls are yellowish
white and finely porous. When the lower wall is brought in focus, it
shows numerous circular pits. These pits represent the pores viewed
from the end. The branches frequently branch or fork.
Branched stone cells also occur in coto bark, acer spicatum,
star-anise, witch-hazel leaf, hemlock, and wild-cherry barks.
Non-branched stone cells are divided into two main groups, as follows:
1. Porous and striated stone cells, and,
2. Porous and non-striated stone cells.
POROUS AND STRIATED STONE CELLS
=Porous and striated= walled stone cells occur in ruellia root,
winter’s bark, bitter root, allspice, and aconite. These stone cells
are shown in Plate 33, Figs. 1, 2, 3, 4, and 5.
The stone cells of ruellia root (Plate 32, Fig. 1) are greatly
elongated, rectangular in form, with thick, white, strongly porous
walls. The central cavity is narrow and is marked with prominent
pores and striations.
The stone cells of winter’s bark (Plate 32, Fig. 2) vary from
elongated to nearly isodiametric. The pores are very large, the light
yellowish wall is irregularly thickened, and the central cavity is
very large. The pores are prominent.
[Illustration: PLATE 31
BRANCHED STONE CELLS
1. Tea leaf (_Thea sinensis_, L.).
2. Witch-hazel bark (_Hamamelis virginiana_, L.).
3. Hemlock bark (_Tsuga canadensis_, [L.] Carr).
4. Wild-cherry bark (_Prunus serotina_, Ehrh.).]
The stone cell of bitter root (Plate 32, Fig. 3) is nearly
isodiametric. The walls are yellowish white and strongly porous and
striated. The central cavity is about equal to the thickness of the
walls.
The stone cell of allspice (Plate 32, Fig. 4) is mostly rounded in
form, and when the outer wall only is in focus it shows numerous
round and elongated pores. The central cavity is filled with masses
of reddish-brown tannin. The striations are very prominent.
The diagnostic stone cell of aconite (Plate 32, Fig. 5) is
rectangular or square in outline; the walls are yellowish and the
central cavity has a diameter many times the thickness of the
wall. The side and surface view of the pores is prominent, and the
striations are very fine.
POROUS AND NON-STRIATED STONE CELLS
=Porous and non-striated stone cells= occur in Ceylon cinnamon, in
calumba root, in dogwood bark, in cubeb, and in echinacea root.
The diagnostic stone cells of Ceylon cinnamon (Plate 33, Fig. 1) are
nearly square in outline; the walls are strongly porous and the large
central cavity frequently contains starch.
The stone cells of calumba root (Plate 33, Fig. 2) vary in shape from
rectangular to nearly square, and the walls are greenish yellow,
unequally thickened, and strongly porous. The typical stone cells
contain several prisms, usually four.
The stone cells of dogwood bark (Plate 33, Fig. 3) have thick, white
walls with simple and branched pores. The central cavity frequently
branches and appears black when recently mounted, owing to the
presence of air.
The stone cells of cubeb (Plate 33, Fig. 4) are very small, mostly
rounded in outline, with a great number of very fine simple pores
which extend from the outer wall to the central cavity. The wall is
yellow and very thick.
The stone cells of echinacea root (Plate 33, Fig. 5) are very
irregular in form; the walls are yellowish and porous, and the
central cavity is very large. A black intercellular substance is
usually adhering to portions of the outer wall.
The color of the walls of the different stone cells is very
variable. In Ceylon cinnamon and ruellia the walls are colorless;
in zanthoxylium, light yellow; in rumex, deep yellow; in cascara
sagrada, greenish yellow.
The pores of stone cells, like the pores of bast fibres, are either
simple or branched, and they may or may not extend through the entire
wall. Many of the shorter pores extend for only a short distance from
the cell cavity.
The width of the cell cavity varies considerably in the stone cells
of the different plants. In aconite (Plate 32, Fig. 5), in calumba
(Plate 33, Fig. 2), and in Ceylon cinnamon (Plate 33, Fig. 1), the
cell cavity is several times greater than the thickness of the cell
wall.
In allspice (Plate 32, Fig. 4), in bitter root (Plate 32, Fig. 3),
the diameter of the cell cavity and the thickness of the wall are
about equal. In cubeb (Plate 33, Fig. 4), in ruellia (Plate 32, Fig.
1), the wall is thicker than the diameter of the cell cavity.
The cavity of many stone cells contains no characteristic
cell contents. In other stone cells the cell contents are as
characteristic as the stone cell. The stone cells of both Saigon and
Ceylon cinnamon (Plate 33, Fig. 1) contain starch; the stone cells
of calumba (Plate 33, Fig. 2) contain prisms of calcium oxalate; the
stone cells of allspice and sweet-birch bark contain tannin.
In cross-sections, stone cells occur singly, as in Saigon cinnamon
(Plate 34, Fig. 1), ruellia (Plate 34, Fig. 2); in groups, as in
cascara sagrada (Plate 34, Fig. 3); and in continuous bands, as in
Saigon cinnamon (Plate 34, Fig. 4).
In powdered drugs, stone cells, like bast fibres, occur singly, as
in ruellia, calumba, etc.; or in groups, as in cascara sagrada,
witch-hazel bark, etc. In most powders they occur both singly and in
groups.
The individual stone cells are mostly entire, as in ruellia, calumba,
allspice, echinacea, etc. In cascara sagrada many of the stone cells
are broken when the closely cemented groups are torn apart in the
milling process. Many of the branched stone cells of witch-hazel bark
and leaf, wild cherry, etc., also occur broken in the powder.
[Illustration: PLATE 32
POROUS AND STRIATED STONE CELLS
1. Ruellia root (_Ruellia ciliosa_, Pursh.).
2. Winter’s-bark (_Drimys winteri_, Forst.).
3. Bitterroot (_Apocynum androsæmifolium_, L.).
4. Allspice (_Pimenta officinalis_, Lindl.).
5. Aconite (_Aconitum napellus_, L.).]
[Illustration: PLATE 33
POROUS AND NON-STRIATED STONE CELLS
1. Ceylon cinnamon (_cinnamomum zeylanicum_, Nees).
2. Calumba root (_Jateorhiza palmata_, [Lam.] Miers).
3. Dogwood root bark (_Cornus florida_, L.).
4. Cubeb (_Piper cubeba_, L., f.)
5. Echinacea (_Echinacea angustifolia_, D.C.).]
[Illustration: PLATE 34
1. Saigon cinnamon.
2. Ruellia root (_Ruellia ciliosa_, Pursh.).
3. Cascara sagrada (_Rhamnus purshiana_, D.C.).
4. Saigon cinnamon.]
The walls of all stone cells are composed of lignin.
The form of stone cells varies greatly; in aconite the stone cells
are quadrangular; in ruellia they are rectangular; in pimenta,
they are circular or oval in outline; in most stone cells they are
polygonal.
The lignified walls of stone cells are stained red with a solution of
phloroglucin and hydrochloric acid, and the walls are stained yellow
by aniline chloride.
ENDODERMAL CELLS
The =endodermal cells= of the different plants vary greatly in form,
color, structure, and composition of the wall, yet these different
endodermal cells may be divided into two groups: first, thin-walled
parenchyma-like cells, and secondly, thick-walled fibre-like cells.
In the thin-walled endodermal cells the walls are composed of
cellulose, and the cell terminations are blunt or rounded. When the
drug is powdered, the cells break up into small diagnostic fragments.
In the thick-walled endodermal cells, the walls are lignified and
porous, and the ends of the cell are frequently pointed and resemble
fibres.
Sarsaparilla root, triticum, convallaria, and aletris have
thick-walled endodermal cells.
STRUCTURE OF ENDODERMAL CELLS
The endodermal cells of sarsaparilla root (Plate 35, Fig. 1) are
never more than one layer in thickness. The walls are porous and of
a yellowish-brown color. Alternating with the thick-walled cell is a
thin-walled cell, which is frequently referred to as a passage cell.
The endodermal cells of triticum (Plate 35, Fig. 2) are yellowish,
and the walls are porous and striated. There are one or two layers
of cells. The cells forming the outer layer have very thin outer but
thick inner walls, while the cells forming the inner layer are more
uniform in thickness.
The endodermal cells of convallaria (Plate 35, Fig. 3) are yellowish
white in color, and the walls are porous and striated. The outer wall
of the layer of cells is thinner than the inner wall. The innermost
layer of cell is more uniformly thickened.
[Illustration: PLATE 35
CROSS-SECTIONS OF ENDODERMAL CELLS OF
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. Triticum (_Agropyron repens_, L.).
3. Convallaria (_Convallaria majalis_, L.).
4. Aletris (_Aletris farinosa_, L.).]
The endodermal cells of aletris (Plate 35, Fig. 4) are yellowish
brown, slightly porous and striated. There are one or two layers of
these cells, and two of the smaller cells usually occupy a space
similar to that occupied by the radically elongated single cell.
On a longitudinal view, the endodermal cells of sarsaparilla
triticum, convallaria, and aletris appear as follows:
Those of sarsaparilla (Plate 36, Fig. 1) are greatly elongated, the
ends of the cells are blunt or slightly pointed, and the walls appear
porous and striated.
Those of triticum (Plate 36, Fig. 2) are elongated, the walls are
porous and striated, and the outer wall is much thinner than the
inner wall. The end wall between two cells frequently appears common
to the two cells.
Those of convallaria (Plate 36, Fig. 3) are elongated, and the end
wall is usually blunt. The outer wall is thinner than the inner wall.
Those of aletris (Plate 36, Fig. 4) are fibre-like in appearance; the
ends of the cells are pointed and the wall is strongly porous. The
longitudinal view of these cells is shown in plate 36.
HYPODERMAL CELLS
=Hypodermal cells= occur in sarsaparilla root and in triticum.
In the cross-section of sarsaparilla root (Plate 37, Fig. 1) the
hypodermal cells are yellowish or yellowish brown. The outer wall is
thicker than the inner wall, and the cell cavity is mostly rounded,
and contains air. The walls are porous and finely striated. On
longitudinal view, the hypodermal cells of sarsaparilla (Plate 37,
Fig. 2) are greatly elongated, and the outer and side walls are
thicker than the inner walls. The ends of the cells are blunt and
distinct from each other.
In cross-section, the hypodermal cells of triticum (Plate 37, Fig. 3)
are nearly rounded in outline, and the walls are of nearly uniform
thickness. In longitudinal view (Plate 37, Fig. 4) the same cells
appear parenchyma-like, and the walls between any two cells appear
common to the two cells.
[Illustration: PLATE 36
LONGITUDINAL SECTIONS OF ENDODERMAL CELLS
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. Triticum (_Agropyron repens_, L.).
3. Convallaria (_Convallaria majalis_, L.).
4. Aletris (_Aletris farinosa_, L.).]
[Illustration: PLATE 37
HYPODERMAL CELLS
1. Cross-section sarsaparilla root (_Smilax officinalis_, Kunth).
2. Longitudinal section sarsaparilla root (_Smilax officinalis_,
Kunth).
3. Cross-section triticum (_Agropyron repens_, L.).
4. Longitudinal section triticum (_Agropyron repens_, L.).]
CHAPTER IV
ABSORPTION TISSUE
Most plants obtain the greater part of their food, first, from the
soil in the form of a watery solution, and, secondly, from the air
in the form of a diffusible gas. In a few cases all food material is
obtained from the air, as in the case of epiphytic plants. In such
plants, the aerial roots have a modified outer layer--velamen--which
functions as a water-absorbing and gas-condensing tissue. Many
xerophytic plants absorb water through the trichomes of the leaf.
Such absorption tissue enables the plant to absorb any moisture that
may condense upon the leaf and that would not otherwise be available
to the plant. The water-absorbing tissue of roots is restricted to
the root hairs, which are found, with few exceptions, only on young
developing roots.
ROOT HAIRS
=Root hairs= usually occur a short distance back of the root cap.
There is, in fact, a definite zone of the epidermis on which the root
hairs develop. This zone is progressive. As the root elongates the
root hairs continue to develop, the zone of hairs always remaining at
about the same distance from the root cap. With the development of
new zones of growth the hairs on the older zone die off and finally
become replaced by an epidermis, or a periderm, except in the case of
sarsaparilla root, and possibly other roots that have persistent root
hairs.
Each root hair is an outgrowth from an epidermal cell (Plate 38, Fig.
3). The length of the hair and its form depend upon the nature of the
soil, whether loose or compact, and upon the amount of water present.
A root hair is formed by the extension of the peripheral wall of
an epidermal cell. At first this wall is only slightly papillate,
but gradually the end wall is extended farther and farther from
the surface of the root, caused by the development of side walls by
the growing tip of the root hair until a tube-like structure, root
hair, is produced. The root hair is then a modified epidermal cell.
The protoplast lines the cell, and the central part of the root
hair consists of a large vacuole filled with cell sap. The wall of
the root hair is composed of cellulose, and the outermost part is
frequently mucilaginous. As the root hairs develop, they become bent,
twisted, and of unequal diameter, as a result of growing through
narrow, winding soil passages. During their growth, the root hairs
become firmly attached to the soil particles. The walls of root hairs
give an acid reaction caused by the solution of the carbon dioxide
excreted by the root hair. The acid character of the wall attracts
moisture, and in addition has a solvent action on the insoluble
compounds contained in the soil. It will thus be seen that the method
of growth, structure, composition, and reaction of the wall of the
root hair is perfectly suited to carry on the work of absorbing the
enormous quantities of water needed by the growing plant. It is
a well-known fact that when two solutions of unequal density are
separated by a permeable membrane, the less dense liquid will pass
through the membrane to the denser liquid. The wall of the root hair
acts like an osmotic membrane. The less dense watery solution outside
the root hair passes through its wall and into the denser cell sap
solution. As the solution is absorbed, it passes from the root hair
into the adjoining cortical parenchyma cells.
It is a fact that root hairs are seldom found in abundance on
medicinal roots. This is due to the fact that root hairs occur
only on the smaller branches of the root, and that when the root
is pulled from the ground the smaller roots with their root hairs
are broken off and left in the soil. For this reason a knowledge of
the structure of root hairs is of minor importance in the study of
powdered drugs. An occasional root hair is found, however, in most
powdered roots, but root hairs have little or no diagnostic value,
except in false unicorn root and sarsaparilla. When false unicorn
root is collected, most of the root hairs remain attached to the
numerous small fibrous roots, owing to the fact that these roots are
easily removed from the sandy soil in which the plants grow. The
root hairs of false unicorn are so abundant and so large that they
form dense mats, which are readily seen without magnification. These
hairs are, therefore, macroscopically as well as microscopically
diagnostic. The root hairs of false unicorn (Plate 39, Fig. 2) have
white, wavy, often decidedly indented walls. The terminal, or end
wall, is rounded and much thicker than the side walls.
[Illustration: PLATE 38
CROSS-SECTION OF SARSAPARILLA ROOT (_Smilax officinalis_, Kunth)
1. Epidermal cell developing into a root hair.
2. Developing root hair.
3. Nearly mature root hair.
4. Hypodermal cells.]
[Illustration: PLATE 39
ROOT HAIRS (Fragments)
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. False unicorn root (_Helonias bullata_, L.).]
In sarsaparilla (Plate 39, Fig. 1) the root hairs are curved and
twisted. The end wall is thicker than the side walls. In some hairs
the walls are as thick as the walls of the thin-walled bast fibres.
This accounts for the fact that the root hairs are persistent on
even the older portions of sarsaparilla root, and it serves also to
explain why these root hairs remain on the root even after being
pulled from the firmly packed earth in which the root grows.
WATER ABSORPTION BY LEAVES
In many xerophytic terrestrial plants, the trichomes occurring on
leaves act as a water-absorbing tissue. In such plants the walls
of the hairs are composed largely of cellulose. It is obvious that
these hairs absorb the water of condensation caused by dew and light
rains--water which could not reach the plant except by such means.
There is no special tissue set aside for the absorption of gases from
the air. Carbon dioxide, which contributes the element carbon to the
starch formed by photosynthesis, enters the leaf by way of the stoma
and lenticels. The structure and the chief functions of these will be
considered under aërating tissue.
CHAPTER V
CONDUCTING TISSUE
All cells of which the primary or secondary function is that
of conduction are included under conducting tissue. It will be
understood how important the conducting tissue is when the enormous
quantity of water absorbed by a plant during a growing season is
considered. It will then be realized that the conducting system must
be highly developed in order to transport this water from one organ
to another, and, in fact, to all the cells of the plant. Special
attention must be given to the occurrence, the structure, the
direction of conduction, and to the nature of the conducted material.
The cells or cell groups comprising the conducting tissue are vessels
and tracheids, sieve tubes, medullary ray cells, latex tubes, and
parenchyma.
VESSELS
=Vessels= and =tracheids= form the principal upward conducting tissue
of plants. They receive the soil water expressed from the cortical
parenchyma cells located in the region of the root, immediately
back of the root hair zone. This soil water, with dissolved crude
inorganic and organic food materials, after entering the vessels
and tracheids passes up the stem. The cells needing water at the
different heights absorb it from the vessels, the excess finally
reaching the leaves. When the stem branches, the water passes into
the vessels of the branches and finally to the leaves of the branch.
In certain special cases the vessels conduct upward soluble food
material. In spring sugary sap flows upward through the vessels of
the sugar maple.
Vessels are tubes, often of great length, formed from a number of
superimposed cells, in which the end walls have become absorbed.
The vessels therefore offer little resistance to the transference
of water from the roots to the leaves of a plant. The combined
length of the vessels is about equal to the height of the plant in
which they occur. The length of the individual vessels varies from a
fraction of a meter up to several meters.
ANNULAR VESSELS
The =annular vessels= are thickened at intervals in the form of rings
(Plate 40, Fig. 1), which extend outward from and around the inner
wall of the vessel. In fact, it is the inner wall which is thickened
in all the different types of vessels. The ring-like thickening
usually separates from the wall when the drug is powdered. Such
separated rings occur frequently in powdered digitalis, belladonna,
and stramonium leaves. Annular vessels are not, however, of
diagnostic importance, because more characteristic cells are found in
the plants in which they occur. Not infrequently a vessel will have
annular thickenings at one end and spiral thickenings at the other.
Such vessels are found in the pumpkin stem (Plate 40, Fig. 1).
Vessels are distinguished from other cells by their arrangement, by
their large size when seen in cross-section, and by the thickening
of the wall when seen in longitudinal sections of the plant or in
powders. The side walls of vessels are thickened in a number of
striking yet uniform ways. The chief types of thickening of the wall,
beginning with one that is the least thickened, are annular, spiral,
sclariform, pitted, and pitted with bordered pores.
SPIRAL VESSELS
In the =spiral vessel= the thickening occurs in the form of a
spiral, which is readily separated from the side walls. This is
particularly the case in powdered drugs, where the spiral thickening
so frequently separates from the cell wall. There are three types of
spiral vessels: those with one (Plate 41, Fig. 1), those with two,
and those with three spirals. Single spirals occur in most leaves;
double spirals occur in many plants (Plate 41, Fig. 2), but they
are particularly striking in powdered squills. Triple spirals are
characteristic of the eucalyptus leaf (Plate 41, Fig. 3); in fact,
they form a diagnostic feature of the powder. Frequently a spirally
thickened wall indicates a developmental stage of the vessel. Many
such vessels are spirally thickened at first, but later, when
mature, an increased amount of thickening occurs and the vessel
becomes a reticulate or pitted vessel. Many mature vessels, however,
are spirally thickened as indicated above. In herbaceous stems and
in certain roots and leaves spiral vessels are associated with the
sclariform reticulate and pitted type. In certain cases a single
spiral band will branch as the vessel matures.
There is a great variation in the amount of spiral thickening
occurring in a vessel. In leaves, particularly, the spiral appears
loosely coiled; while in squills and other rhizomes and roots the
spiral appears as a series of rings. When viewed by high power only
half of each spiral band is visible. At either side of the cell the
exact size and form of the thickening appear in two parallel rows of
dark circles or projections from the walls. This thickening of the
wall is rendered visible from the fact that the light is retarded as
it passes through that portion of the spiral extending from the upper
to the under side of the spiral; while the light readily traverses
the upper and lower cross bands of the vessel.
It should be remembered that, when the upper part of the spiral
vessel is in focus, the bands appear to bend in a direction away from
the eye; while when the under side of the bands are in focus, the
bands appear to bend toward the eye. These facts will show that it
is necessary to focus on both the upper and lower walls in studying
spiral vessels. In double spiral vessels the spirals are frequently
coiled in opposite directions; therefore the bands appear to cross
one another. In eucalyptus leaf the three bands are coiled in the
same direction. In all cases the thickening occurs on all sides of
the wall. Its appearance will, therefore, be the same no matter at
what angle the vessel is viewed.
SCLARIFORM VESSELS
=Sclariform vessels= have interrupted bands of thickening on the
inner walls. Two or more such bands occur between the two side walls.
The series of bands are separated by uniformly thickened portions of
the wall extending parallel to the length of the vessel. Sclariform
vessels are usually quite broad, so that it is necessary to change
the focus several times in order to bring the different series of
bands in focus. The series of bands are usually of unequal width and
length.
[Illustration: PLATE 40
ANNULAR AND SPIRAL VESSELS
1. Pumpkin stem (_Cucurbita pepo_, L.).
2. Two characteristic views of spiral vessels.
3. (_A_) Upper part of spiral vessel in focus.
(_B_) Under part of spiral vessel in focus.
4. Spiral vessel of the disk petal matricaria (_Matricaria
chamomilla_, L.).]
[Illustration: PLATE 41
SPIRAL VESSELS
1. Single spiral vessel of pumpkin stem (_Cucurbita pepo_, L.).
2. Double spiral vessel of squill bulb (_Urginea maritima_, [L.]
Baker).
3. Triple spiral vessel of eucalyptus leaf (_Eucalyptus globulus_,
Labill).]
Sclariform vessels occur in male fern (Plate 42, Fig. 2), calamus,
tonga root (Plate 42, Fig. 3), and sarsaparilla (Plate 42, Fig. 1).
In each they are characteristic. Sclariform vessels, with these few
exceptions, do not occur in drug plants. In fact, drugs derived from
dicotyledones rarely have sclariform vessels. They occur chiefly
in the ferns and drugs derived from monocotyledenous plants. Their
presence or absence should, therefore, be noted when studying
powdered drugs.
RETICULATE VESSELS
=Reticulate vessels= are of common occurrence in medicinal plants. In
fact, they occur more frequently than any other type of vessel. The
basic structure of reticulate vessels (Plate 43, Fig. 1) occurring in
different plants is similar, but they vary in a recognizable way in
different plants (Plate 43, Fig. 2). The walls of reticulate vessels
are thickened to a greater extent than are the walls of spirally
thickened vessels.
PITTED VESSELS
=Pitted vessels= are met with most frequently in woods and
wood-stemmed herbs. There are two distinct types of pitted
vessels--_i.e._, simple pitted vessels and pitted vessels with
bordered pores.
The pitted vessel represents the highest type of cell-wall
thickening. The entire wall of the vessel is thickened, with the
exception of the places where the pits occur. The number and size of
the pits vary greatly in different drugs. In quassia (Plate 44, Fig.
1) the pits are numerous and very small, and the openings are nearly
circular in outline. In white sandalwood (Plate 44, Fig. 3). the pits
are few in number, but when they do occur they are much larger than
are the pits of quassia.
PITTED VESSELS WITH BORDERED PORES
=Pitted vessels with bordered pores= are of common occurrence in the
woody stems and stems of many herbaceous plants (Plate 45, Figs. 3
and 4). In such vessels the wall is unthickened for a short distance
around the pits. This unthickened portion may be either circular or
angled in outline, a given form being constant to the plant in which
it occurs. The pits vary from oval to circular. Pitted vessels with
bordered pores occur in belladonna and aconite stems.
[Illustration: PLATE 42
SCLARIFORM VESSELS
1. Sarsaparilla root (_Smilax officinalis_, Kunth).
2. Male fern (_Dryopteris marginalis_, [L.] A. Gray).
3. Tonga root.]
[Illustration: PLATE 43
RETICULATE VESSELS
1. Hydrastis rhizome (_Hydrastis canadensis_, L.).
2. Musk root (_Ferula sumbul_, [Kauffm.] Hook., f.).]
[Illustration: PLATE 44
PITTED VESSELS
1. Quassia, low magnification (_Picræna excelsa_, [Swartz] Lindl.).
2. Quassia, high magnification.
3. White sandalwood (_Santalum album_, L.).]
[Illustration: PLATE 45
VESSELS
1. Reticulate vessel of calumba root (_Jateorhiza palmata_, [Lam.]
Miers).
2. Reticulate tracheid of hydrastis rhizome (_Hydrastis
canadensis_, L.).
3. Pitted vessel with bordered pores of belladonna stem.
4. Pitted vessel with bordered pores of aconite stem (_Aconitum
napellus_, L.).]
Vessels and tracheids lose their living-cell contents when fully
developed. In the vessels the cell contents disappear at the period
of dissolution of the cell wall.
The walls of vessels and tracheids are composed of lignin, a
substance which prevents the collapsing of the walls when the
surrounding cells press upon them, and which also prevents the
tearing apart of the wall when the vessel is filled with ascending
liquids under great pressure. Lignin thus enables the vessel to
resist successively compression and tearing forces.
Tracheids are formed from superimposed cells with oblique perforated
end walls. The side walls of tracheids are thickened in a manner
similar to those of vessels. The tracheids in golden seal are of a
bright-yellow color, and groups of these short tracheids scattered
throughout the field form the most characteristic part of the
powdered drug. In ipecac root the tracheids are of a porcelain-white,
translucent appearance, and they are much longer than are the
tracheids of golden seal.
The cellulose walls of parenchyma cells are stained blue with
hæmatoxylin and by chlorzinciodide. Cellulose is completely soluble
in a fresh copper ammonia solution.
SIEVE TUBES
=Sieve tubes= are downward-conducting cells. They conduct downward
proteid food material. This fact is easily demonstrated by adding
iodine to a section containing sieve tubes, in which case the sieve
tubes are turned yellow.
Developing sieve tubes have all the parts common to a living cell;
but when fully mature, however, the nucleus becomes disorganized, but
a layer of protoplasm continues to line the cell wall.
Sieve tubes (Plate 46, Fig. 1) are composed of a great number of
superimposed cells with perforated end walls and with non-porous
cellulose side walls. The end walls of two adjoining cells are
greatly thickened and the pores pass through both walls. This
thickened part of the porous end walls of two sieve cells is called
the sieve plate, and it may be placed in an oblique or a horizontal
position.
[Illustration: PLATE 46
1. Longitudinal section of sieve tube (_Cucurbita pepo_, L.).
2. Cross-section of sieve tube just above an end wall--sieve plate.]
In a longitudinal section the sieve tubes are seen to be slightly
bulging at the sieve plate, and through the pores extend protoplasmic
strands. The strands are united on the upper and lower side of
the sieve plate to form the protoplasmic strands of the living
sieve tubes and the callus, layers of dried plants. This callus is
frequently yellowish in color, and in all cases is separated from the
cell wall. In certain plants the sieve plate occurs on the side walls
of the sieve tubes in contact with other sieve tubes.
SIEVE PLATE
=Sieve plates= on cross-section (Plate 46, Fig. 2) are polygonal
in outline, and the pores are either round or angled. Large sieve
tubes and sieve plates occur in pumpkin stem; but, almost without
exception, in drug plants the sieve tubes are small and the sieve
plate is inconspicuous. When the drug is powdered, the sieve tubes
break up into undiagnostic fragments. When studying sections of the
plants, the extent, size, and arrangement of the sieve tubes must
always be noted.
MEDULLARY BUNDLES, RAYS, AND CELLS
Function
The medullary ray cells are the lateral conducting cells of the
plant. They conduct outwardly the water and inorganic salts brought
up from the roots by the vessels and tracheids; and they conduct
inwardly toward the centre of the stem the food material manufactured
in the leaves and brought down by the sieve cells. The medullary rays
thus distribute the inorganic and organic food to the living cells of
the plant, and they conduct the reserve food material to the storage
cells, and, lastly, they function in certain plants as storage cells.
Occurrence
The form, size, wall structure, and the distribution of the medullary
ray bundles, rays, and cells are best ascertained by studying:
first, the cross-section of the plant; secondly, the radial section;
and, thirdly, the tangential section.
Students should be careful to distinguish between the medullary ray
bundle, the medullary ray, and the medullary ray cell. In some plants
the bundles are only one cell wide, but in other plants the medullary
ray bundle is more than one cell wide, frequently several cells wide.
THE MEDULLARY RAY BUNDLE
The =medullary ray bundle= is made up of a great many medullary ray
cells. These bundles (Plate 106, Fig. 5) are of variable length,
height, and width. The bundles are isolated, and they occur among
and separate the other cells of the plants in which they occur.
Tangential sections show the medullary ray bundle in cross-section.
Such sections are lens-shaped, and they show both the width and the
height of the medullary ray bundle. The length of the medullary ray
bundle is shown in cross-sections.
THE MEDULLARY RAY
The =medullary ray= (Plate 47) is a term used to indicate that part
of a medullary ray bundle which is seen in cross-sections and in
radial sections. In cross-sections the length of the ray will be as
great as the length of the bundle, and the width of the ray will be
as great as the width of the medullary ray bundle at the point cut
across. In longitudinal sections the medullary ray will differ in
height according to the thickness of the bundle at the point cut.
When the medullary rays extend from the centre of the stem to the
middle bark, they are termed primary medullary rays; when they extend
from the cambium circle to the middle bark, they are termed secondary
medullary rays. As the plant grows, the diameter of the organ becomes
greater and the number of medullary rays are increased. In each of
these cases the medullary rays may be one or more than one cell wide,
according to whether the medullary ray bundle is one or more than one
cell wide. Even in the same plant the width of the medullary rays
will vary if the bundle is more than one cell wide, according to
width of the medullary ray bundle at the point cut across.
[Illustration: PLATE 47
RADIAL LONGITUDINAL SECTION OF WHITE SANDALWOOD
(_Santalum album_, L.)
1. Medullary ray.
2. Wood fibres and wood parenchyma.]
On cross-section the medullary rays are seen to vary greatly. In many
plants they are more or less straight radial lines, as in quassia
(Plate 105, Fig. 2); while in other plants they form wavy lines
where they bend or curve around the conducting cells, as in piper
methysticum, kava-kava (Plate 48, Fig. A).
In the study of powdered drugs the radial view of the medullary rays
is most frequently seen.
In a perfect radial section (Plate 107, Fig. 2) the medullary rays
are seen as tiers of cells in contact throughout their long diameter,
and they run at right angles to the long diameter of the other cells.
This view of the rays shows the length and height of the medullary
ray. In logwood the rays are often forty cells high. In powdered
barks, woods (Plate 47), and woody roots the radial view of the
medullary rays is frequently diagnostic.
In guaiacum officianale wood the medullary rays are one cell wide on
cross-section, and up to six cells high on the tangential section.
In santalum album the rays are from one to three cells wide on
cross-section, and up to six cells high on tangential section. In the
greater number of plants the rays are more than one cell wide.
THE MEDULLARY RAY CELL
The =medullary ray cell= (Plate 48, Fig. 1) is one of the individual
cells making up the medullary ray bundle and the medullary ray.
The cross-sections of the cells which are seen in tangential sections
show the cells to be mostly circular in outline when they occur in
the central portion of medullary ray bundles of more than two cells
in width; but they are more irregular in outline when the medullary
ray bundle is only one cell wide. Even the cells of the three or more
cell-wide bundles have irregular, outlined cells at the ends of the
bundle and on the sides in contact with the other tissues.
The length and height of the medullary ray cell are shown in radial
sections; while the width and length of the medullary ray cells are
shown in cross-sections.
Structure of Cells
The structure of the individual cells forming the medullary rays
differs greatly in different plants, but is more or less constant in
structure in a given species.
The medullary rays of the wood usually have strongly pitted side and
end walls, while the medullary rays of most barks are not at all, or
only slightly, pitted. In most plants the cells are of nearly uniform
size. Frequently, however, the cells vary in size in a given ray, as
shown in the cross-section of kava-kava.
Arrangement of the Cells in a Ray
The union of any two cells in a ray is also of importance. In
quassia the medullary ray cells have oblique end walls, so that on
cross-section the line of union between two cells is an oblique
wall. In most plants the medullary ray cells have blunt or square or
oblique end walls, so that the line of union is a straight line.
In most plants the cells are much longer than broad, but the cells of
sassafras bark are nearly as broad as long.
The walls of the cortical medullary ray cells and the medullary rays
of most roots and stems of herbs are composed of cellulose; while
the walls of medullary ray cells occurring in woods are frequently
lignified.
There is a great variation in the character of the cell contents of
medullary rays. In white pine bark (Plate 48, Fig. B1) are deposits
of tannin; in quassia wood, starch; in canella alba, rosette crystals
of calcium oxalate, etc.
LATEX TUBES
Living =latex tubes=, like sieve tubes, have a layer of protoplasm
lining the walls, and, in addition, have numerous nuclei. In drug
plants the nuclei are not distinguishable, but the protoplasm is
always clearly discernible.
[Illustration: PLATE 48
_A._ Cross-section of kava-kava root (_Piper methysticum_,
Forst., f.).
1. Unequal diameter medullary ray cells.
2. Vessels.
3. Wood parenchyma.
4. Wood fibres.
_B._ Cross-section of white pine bark (_Pinus strobus_, L.).
1. Wavy medullary rays with tannin.
2. Parenchyma cells.
3. Sieve cells.]
Latex tubes function both as storage and as conducting cells. They,
like the sieve tubes, contain proteid substances chiefly, yet
frequently starch is found. The cells bordering the latex tubes
absorb from them, as needed, the soluble food material. While our
knowledge concerning the function of latex in some plants is meagre,
still in other plants it is practically certain that the latex is
composed of nutritive substances which are utilized by the plant as
food. In certain other plants the latex appears to be used as a means
of resisting insect attacks and as a protection against injury.
There are two types of latex tubes common to plants, namely, latex
cells and latex vessels. Latex tubes developing from a single cell do
not differ materially from a latex tube originating from the fusion
of several cells. In each case the latex tube branches to such an
extent that it bears no resemblance to ordinary cells. It would seem
that the ultimate branches are formed and develop in much the same
manner as root hairs--that is, by a growing tip of the branch. A
mature plant may therefore have latex tubes with almost numberless
branches (Plate 50, Fig. 1) and be of very great length.
The branches of latex tubes develop in such an irregular manner that
it is possible to obtain a cross and a longitudinal section of the
latex tubes by making a cross-section of stem. Such a section is
shown in the drawing of the cross-section of the rhizome of black
Indian hemp (Plate 49, Fig. B).
The color of the latex in medicinal plants varies from a gray white
in papaw (carica papaya), aromatic sumac, black Indian hemp, and
bitter root, to white in the opium poppy, light orange in celandine,
and deep orange in bloodroot (Plate 50, Fig. 2). In each of these
cases it is the latex which yields the important medicinal products.
PARENCHYMA
The larger amount of plant tissue is composed of =parenchyma= cells.
These cells vary from square to oblong, or they may be irregular and
branched. The end walls are square or blunt, and the wall is composed
of cellulose, with the exception of the wood parenchyma, which has
lignified walls.
There are seven characteristic types of parenchyma cells: (1)
cortical parenchyma, (2) pith parenchyma, (3) wood parenchyma,
(4) leaf parenchyma, (5) aquatic plant parenchyma, (6) endosperm
parenchyma, (7) phloem parenchyma.
[Illustration: PLATE 49
_A._ Cross-section of black Indian hemp (_Apocynum cannabinum_, L.).
1. Longitudinal section of a latex tube.
2. Cross-section of latex tube.
3. Parenchyma.
_B._ Cross-section of a part of black Indian hemp root.
4. Cross-section of a large latex tube.
5. Parenchyma.]
[Illustration: PLATE 50
LATEX VESSELS
1. Radial-longitudinal section of dandelion root (_Taraxacum
officinale_, Weber).
2. Cross-section of sanguinaria root (_Sanguinaria canadensis_, L.).
3. Cross-section of dandelion root.]
Parenchyma cells, cortical, pith, aquatic plant, leaf, flower,
and endosperm, conduct in all directions--upward, downward, and
laterally. The direction of conduction depends upon the needs of the
different cells forming the plant. The fluids pass from the cell with
an abundance of cell sap to the cell with less cell sap. In this wall
all cells are provided with food.
Parenchyma cells conduct water absorbed by the roots and soluble
carbohydrate material chiefly.
The walls of all the different types of parenchyma cells are composed
of cellulose with the exception of the wood parenchyma cells,
the walls of which are lignified. The end walls of non-branched
parenchyma cells and the cell terminations of branched cells are very
blunt.
CORTICAL PARENCHYMA
=Cortical parenchyma= (Plate 51) differs greatly in size, thickness
of the walls, and arrangement. A study of the longitudinal sections
of different parts of medicinal plants reveals the fact that the
cortical parenchyma cells form superimposed layers in which the end
walls are either parallel, in which case the arrangement resembles
that of several rows of boxes standing on end, or the end walls of
the cells alternate with each other, in which case the arrangement is
similar to that of the arrangement of the bricks in a building.
In certain plants the cortical parenchyma cells are long and narrow
and rectangular in shape, while in other plants the cells, although
still rectangular in outline, are very broad and approach the square
form.
All typical cortical parenchyma cells have uniformly thickened
non-pitted walls. In most barks the parenchyma cells beneath the
bark are elongated tangentially, but are very narrow radially. The
cells are always arranged around intercellular spaces, which vary
from triangular, quadrangular, etc., according to the number of cells
bordering the intercellular space.
PITH PARENCHYMA
=Pith parenchyma= (Plate 52) differs from cortical parenchyma cells
chiefly in the character of the walls, which are usually thicker and
always pitted.
[Illustration: PLATE 51
PARENCHYMA CELLS
1. Longitudinal section of the cortical parenchyma of celandine
root (_Chelidonium majus_, L.) 2. Cross-section of the cortical
parenchyma of sarsaparilla root (_Smilax officinalis_, Kunth).]
[Illustration: PLATE 52
_A._ Longitudinal section of the pith parenchyma of grindelia stem
(_Grindelia squarrosa_, [Pursh] Dunal).
1. Cell cavity.
2. Cross-section of the porous end wall.
3. Surface view of the porous side wall.
_B._ Cross-section of the pith parenchyma of grindelia stem.
1. Cell cavity.
2. Porous walls.
3. Pitted end walls.]
LEAF PARENCHYMA
The =parenchyma cells= (Plate 109, Fig. 1) of leaves, of flower
petals, and the parenchyma cells of some aquatic plants are branched;
that is, each cell has more than two cell terminations. These cell
terminations are frequently quite attenuated and usually very blunt.
Such a cell structure provides for a greater amount of intercellular
space and a maximum exposure of surface. This arrangement makes it
possible for the parenchyma cells of the leaf to absorb more readily
the enormous amount of carbon dioxide needed in the photosynthetic
process.
AQUATIC PLANT PARENCHYMA
The =parenchyma of aquatic plants= (Plate 59) has large intercellular
spaces formed by the chains of cells.
WOOD PARENCHYMA
=Wood parenchyma= (Plate 105, Fig. 3) cells are the narrowest
parenchyma cells occurring in the plant. Their walls are always
lignified and strongly pitted, and in some cases the end walls common
to two cells are obliquely placed.
PHLOEM PARENCHYMA
=Phloem parenchyma= (Plate 100, Fig. 8) cells are usually associated
with sieve cells. They are very long, narrow, and have thin,
non-pitted walls. The thinness of the walls undoubtedly enables the
cells to conduct diffusible food substance more quickly than the
cortical parenchyma cells.
PALISADE PARENCHYMA
=Palisade parenchyma= of leaves is of the typical parenchyma shape
and the end walls are placed nearly on a plane, even when more than
one layer is present. The cells are very small, however, and the
walls are very thin and non-pitted.
CHAPTER VI
AERATING TISSUE
The =aerating tissue= of the plant performs a threefold function:
first, it permits the exchange of gases during photosynthesis;
secondly, it permits the entrance of oxygen and the exit of carbon
dioxide during respiration; and, thirdly, it permits the exit of the
excess of water absorbed by the plant.
The above functions are carried on by the stomata, the water-pores,
the lenticels, and the intercellular spaces of the plant. The stoma
functions as the chief channel for the passage of CO₂-laden air into
the leaf and of oxygen-laden air from the leaf to the atmosphere. The
stoma also functions as an organ of transpiration, since through the
stoma a large part of the excess water of the plant passes off into
the air.
WATER-PORES
In certain plants the primary epidermis is provided with openings
resembling stomata, but unlike stomata the orifice remains open, and
instead of being located on the upper or lower surface of the leaf,
they are located on the margin of leaves immediately outward from the
veins. Water is given off to the atmosphere from these openings. Such
an opening is usually designated as a water-pore.
STOMATA
The chief external openings of the epidermis of leaves, of herbs, and
of young wood stems are known as stomata. Surrounding the stoma are
two cells known as guard cells.
=Guard cells= differ greatly in form, in size, in arrangement, in
occurrence, in association, in abundance (Plates 53, 54, and 55), and
in color. The guard cells surrounding the stoma vary in form from
circular to lens-shaped. In most leaves the outline of the guard
cells is rounded or has a curved outline; but in a few cases the
guard cells have angled outlines.
[Illustration: PLATE 53
1. Stoma and surrounding cells of aconite stem (_Aconitum
napellus_, L.).
2. Stoma and angled striated walled surrounding cells of peppermint
stem (_Mentha piperita_, L.). 3. Stoma and elongated surrounding
cells of lobelia stem (_Lobelia inflata_, L.).]
[Illustration: PLATE 54
TYPES OF STOMA
1. Under epidermis of short buchu (_Barosma betulina_, [Berg.]
Bartling and Wendl., f.) showing stoma and deposits of hesperidin.
2. Under epidermis of Alexandria senna (_Cassia acutifolia_,
Delile) showing stoma and thick-angled walled surrounding cells.
3. Upper epidermis of eucalyptus leaf (_Eucalyptus globulus_,
Labill.) showing sunken stoma and slightly beaded walled
surrounding cells.
4. Under epidermis of belladonna leaf (_Atropa belladonna_, L.)
showing stoma and wavy, striated, walled epidermal cells.]
The =arrangement of the surrounding cells= of the stoma is one of the
most important characteristics of the different leaves. As a rule the
number of surrounding cells about a stoma is constant for a given
species. In senna leaves (Plate 54, Fig. 2) there are normally two
surrounding cells about each guard cell, while in coca there are four
(Plate 55, Fig. 1). In senna the long diameter of the surrounding
cells is parallel to the long diameter of the guard cells; but in
coca the long diameter of two surrounding cells is at right angles to
the long diameter of the guard cells, while two cells are parallel to
the long diameter of the guard cells.
In most leaves there are more than two cells around the guard cells.
The form and size of the surrounding cells must always be considered.
In most leaves they are variable in size and form.
Guard cells occur first, even with the surface of the leaf (Plate 56,
Fig. A); secondly, above the surface of the leaf (Plate 56, Fig. B);
and, thirdly, below the surface of the leaf. (Plate 56, Fig. C). Only
one of the above types occurs in a given species of plant. That is,
plants with stomata above the surface of the leaf do not have stomata
on a level with or below the leaf surface.
The number of stomata on a given surface of a different leaf varies
considerably.
In many of the medicinal leaves stomata occur only on the under
surface of the leaf. In other leaves stomata occur on both surfaces
of the leaf; but in such cases there are a greater number on the
under surface.
In certain leaves the long diameter of the guard cells is parallel to
the length of the leaf; in other cases the long diameter of the stoma
is arranged at right angles to the length of the leaf.
In other leaves the arrangement is still more irregular, the guard
cells assuming all sorts of positions in relation to the length of
the leaf.
[Illustration: PLATE 55
LEAF EPIDERMI WITH STOMA
1. Under epidermis of coca leaf (_Erythroxylon coca_, Lam.) with
stoma on a level with the surface.
2. Under epidermis of false buchu (_Marrubium peregrinum_, L.) with
stoma below the level of the surface.
3. Upper epidermis of deer tongue (_Trilisa odoratissima_, [Walt.]
Cass.) with stoma above the leaf surface.]
[Illustration: PLATE 56
_A._ Cross-section of belladonna leaf (_Atropa belladonna_, L.).
1, Epidermal cells; 2, Guard cells even with the leaf surface; 3,
Surrounding cells; 4, Air space below the guard cells; 5, Palisade
cells; 6, Mesophyll cells. _B._ Cross-section of deer tongue leaf,
1. Epidermal cells; 2, Guard cells above the surface of the leaf;
3, Surrounding cells; 4, Air space below the guard cells; 5,
Hypodermal cells. _C._ Cross-section of white pine leaf (_Pinus
strobus_, L.). 1, Epidermal and hypodermal cells; 2, Guard cells
below the leaf surface; 3, Surrounding cells; 4, Air space below
the guard cells; 5, Parenchyma cells with projecting inner walls.]
The =relation of the stoma to surrounding cells= is best shown in
cross-sections of the leaf. In powders the relationship of the stoma
to the surrounding cells is, however, readily ascertained. If the
guard cells come in focus first, they are above the surface; if the
guard cells and the surrounding cells come in focus at the same time,
the stomata are even with the surface; if the stomata come in focus
after the surrounding cells, they are below the surface of the leaf.
The relationship of the stoma to the surrounding cells should always
be ascertained, not only in cross-sections of the leaf, but also in
powders.
There is the greatest possible variation in the size of guard cells.
This fact must always be kept in mind when studying leaves. This
variation in the size of the guard cells is clearly illustrated by
coca, senna, and by deer’s-tongue. In coca the stomata are very
small; in senna they are larger; while in deer’s-tongue the stomata
are very large.
The width and length of the stoma or opening between the guard cells
are of a character which must not be overlooked. Generally speaking,
those leaves which have large guard cells will have correspondingly
large stomata.
The guard cells usually contain chloroplasts showing various stages
of decomposition.
In bay-rum leaf the guard cells are of a bright reddish-brown color,
but in most leaves the guard cells are colorless.
LENTICELS
=Lenticels= are small openings occurring in the bark of plants.
The lenticels bear the same relationship to the stem that the
stomata do to the leaves. Lenticels, like stomata, have a threefold
function--namely, exchange of gases in photosynthesis, in
respiration, and the giving off of water.
Lenticels are macroscopically as well as microscopically important.
When unmagnified the lenticels are circular, lens-shaped, or
irregular in outline. They are arranged in parallel longitudinal
lines or parallel transverse lines, or they are irregularly
scattered. The latter is the usual arrangement. In most cases they
are elevated slightly above the surface of the bark. In root barks
particularly the lenticels stand out prominently from the surface of
the bark and in many cases appear stalked.
The color of the lenticels differs greatly in the different plants.
In acer spicatium they are brown; in witch-hazel they are gray; in
xanthoxylium they are yellowish; and lastly, the number of lenticels
occurring in a given surface of the bark should always be considered.
On cross-sections the lenticel (Plate 57, Fig. 2) is seen to have
a central depressed portion made up of loosely arranged cells.
Bordering the cavity are typical cork cells. The cork cells
immediately surrounding the lenticels are usually darker in color,
and many of the cells are partly broken down.
The size of lenticels will vary according to the type of the
lenticel. In studying sections more attention should be paid to the
character of the cells forming the lenticels than to the size of the
lenticel.
On cross-section the intercellular spaces (Plate 58) are triangular,
quadrangular, or irregular. The spaces between equal diameter
parenchyma cells is triangular if three cells surround the space, and
quadrangular if four cells surround the space, etc. These spaces are
in direct contact with similar spaces that traverse the tissue at
right angles to its long axis.
The branched mesophyll cells of the leaf and aquatic plant parenchyma
(Plate 59) are arranged around irregular cavities. In leaves and
aquatic plants these spaces run parallel to the long axis of the
organ.
In each of the above cases the cavity is formed by the separation of
the cell walls. There is still another type of irregular cavities
which is formed by the dissolution or tearing apart of the cell
walls. Such cavities are found in the stems and roots of many herbs.
The pith cells in the stems of many herbs become torn apart during
the growth of the stem, with the result that large irregular cavities
are formed. These cavities are usually filled with circulatory air.
In the stems of conium, cicuta, angelica, and other larger herbaceous
stems the pith separates into layers. When a longitudinal section
is made of such a stem it is seen to be composed of alternating air
spaces and masses of pith parenchyma.
The intercellular spaces are very large in leaves where enormous
quantities of carbon dioxide are vitalized in photosynthesis.
[Illustration: PLATE 57
CROSS-SECTION OF ELDER BARK (_Sambucus canadensis_, L.). 1.
Periderm. 2. Lenticel. 3. Phellogen.]
[Illustration: PLATE 58
INTERCELLULAR AIR SPACES
_A._ Cross-section of uva-ursi leaf (_Arctostaphylos uva-ursi_,
[L.] Spreng.).
1. Irregular intercellular air spaces.
_B._ Cross-section of the cortical parenchyma of sarsaparilla
root (_Smilax officinalis_, Kunth). 1, Triangular intercellular
spaces; 2, Quadrangular intercellular air spaces; 3, Pentagular
intercellular air spaces.]
[Illustration: PLATE 59
IRREGULAR INTERCELLULAR AIR SPACES
1. Skunk-cabbage (_Symplocarpus fœtidus_, [L.] Nutt.)
2. Calamus rhizome (_Acorus calamus_, L.).]
In the rhizome of calamus and other aquatic plants the intercellular
spaces are very large. The cells of these plants are arranged in
the form of branching chains of cells which thus provide for large
intercellular spaces.
The cells of the middle layer of flower petals, like the mesophyll of
leaves, is loosely arranged owing to the peculiar branching form of
the cells.
Seeds and fruits contain, as a rule, few or no intercellular spaces.
CHAPTER VII
SYNTHETIC TISSUE
Under synthetic tissue are grouped all tissues and cells which form
substances or compounds other than protoplasm. Such compounds are
stored either in special cavities or in the cells of the plant, as
the glandular hairs; internal secreting cavities of barks, stems,
leaves, fruits, seeds, and flowers; photosynthetic cells or cells
with chlorophyll, and the parenchymatic cells which form starch,
sugar, fats, alkaloids, etc.
PHOTOSYNTHETIC TISSUE
The most important non-glandular synthetic tissue is the
photosynthetic tissue, which is composed of the chlorophyll-bearing
cells of the plant. These are the so-called green cells of leaves, of
stems of herbs, of young woody stems, and in the older woody stems of
plants like wild cherry, birch, etc. The greater part of the tissue
of leaves is composed of chlorophyll-bearing cells.
Leaves collectively constitute the greatest synthetic manufacturing
plant in the world, because the green cells of the leaf produce most
of the food of men and animals. The two compounds utilized in the
manufacture of food are carbon dioxide (CO₂) and water (H₂O). These
two compounds are combined by chlorophyll through the agency of light
into starch. Chemically this reaction may be expressed as follows:
6CO₂ + 5H₂O = 2C₆H₁₀O₅ + 6O₂.
During the day a large quantity of starch is formed. At night through
the action of a ferment the excess of starch remaining in the leaf
is converted into sugar (C₆H₁₂O₆) - C₆H₁₀O₅ + H₂O = C₆H₁₂O₆. In this
form it is distributed to the living cells of the plant. The presence
or absence of starch in leaves is easily ascertained by placing the
leaf in hot alcohol to remove the chlorophyll, and by adding Lugol’s
solution. If starch is present, the contents of the cells will become
bluish black; but if no starch is present, the cells remain colorless.
GLANDULAR TISSUE
The =glandular tissue= of the plant is divided into two groups,
according to where it occurs. These groups are, first, =external=
glandular tissue, and secondly, =internal= glandular tissue. The most
important external glandular tissue is composed of the glandular
hairs. These are divided into two groups: first, =unicellular=; and
secondly, =multicellular= glandular hairs.
UNICELLULAR GLANDULAR HAIRS
The =unicellular glandular hairs= are either sessile or stalked.
=Sessile unicellular hairs= occur in digitalis leaves.
=Stalked unicellular hairs= of digitalis are shown on Plate 60, Fig.
2.
=Unicellular uniseriate stalked glandular hairs= occur on the stems
of the common house geranium (Plate 61, Fig. 2), on the leaves of
butternut, the leaves and stems of marrubium peregrinum (Plate 98,
Fig. 5), and in arnica flowers. The stalk varies from two to ten
cells; in eriodictyon the cells vary from four to eight cells.
Unicellular multiseriate stalked glandular hairs are not of common
occurrence.
MULTICELLULAR GLANDULAR HAIRS
=Multicellular glandular hairs= are divided into two groups: first,
sessile; and secondly, stalked hairs.
Multicellular sessile glandular hairs occur on the leaves of
peppermint (Plate 60, Fig. 3), horehound (Plate 97, Fig. 7), and
in hops (Plate 60, Fig. 4). In each of these hairs there are eight
secretion cells.
=Stalked glandular hairs= are divided into two groups: first,
uniseriate stalked; and secondly, multiseriate stalked glandular
hairs.
=Multicellular uniseriate stalked glandular hairs= occur on the
leaves of tobacco (Plate 61, Fig. 4), belladonna (Plate 61, Fig. 1),
and digitalis (Plate 60, Fig. 2), and of the fruit of rhus glabra.
[Illustration: PLATE 60
GLANDULAR HAIRS
1. Kamala (_Mallotus philippinensis_, [Lam.] [Muell.] Arg.).
2. Digitalis leaf (_Digitalis purpurea_, L.).
3. Peppermint leaf (_Mentha piperita_, L.).
4. Lupulin.
5. Cannabis indica leaf (_Cannabis saliva_, L.).]
=Multicellular multiseriate stalked glandular hairs= occur on the
stems and leaves of cannabis indica (Plate 60, Fig. 5).
In the glandular hair of kamala (Plate 60, Fig. 1) the number of
secretion cells is variable and papillate in form, and the cuticle is
separated from the secretion cells.
In the glandular hair of hops the outer wall or cuticle is torn away
from the secretion cells, and the cavity thus formed serves as a
storage cavity. This distended cuticle of the hops shows the outline
of the cells from which it was separated.
In the glandular hairs of the mints the secreted products (volatile
oils) are stored between the secretion cells and the outer detached
cuticle. This cuticle is elastic, and it becomes greatly distended as
the volatile oil increases in amount.
In many of the so-called glandular hairs, tobacco, belladonna
geranium, etc., the synthetic products are retained in the glandular
cells, there being no special cavity for their storage.
These hairs usually contain an abundance of chlorophyll.
The division wall of multicellular glandular hairs may be vertical,
as in the two-celled hair of digitalis (Plate 60, Fig. 2); as in
horehound (Plate 97, Fig. 6), and as in peppermint (Plate 60, Fig.
3); in this case there are eight cells, and they form a more or less
flat plate of cells.
In other hairs the division wall is horizontal; this produces a chain
of superimposed secreting cells, as in some of the glandular hairs of
belladonna leaf (Plate 61, Fig. 1), etc.
In other hairs the division walls are both vertical and horizontal,
as in tobacco (Plate 61, Fig. 4), henbane (Plate 61, Fig. 3),
belladonna (Plate 61, Fig. 1).
Other characters to be kept in mind in studying glandular hairs are
the following: Color of cell contents; size of the cells, whether
uniform or variable; character of wall, whether smooth or rough.
SECRETION CAVITIES
=Secretion cavities= are divided into three groups, according to the
nature of the origin of the cavity: first, schizogenous cavities,
which originate by a separation of the walls of the secretion cells;
secondly, lysigenous cavities, which arise by the dissolution
of the walls of centrally located secretion cells; and thirdly,
schizo-lysigenous cavities, which originate schizogenously, but later
become lysigenous owing to the dissolution of the outer layers of the
secretion cells.
[Illustration: PLATE 61
STALKED GLANDULAR HAIRS
1. Belladonna leaf (_Atropa belladonna_, L.).
2. Geranium stem (_Geranium maculatum_, L.).
3. Henbane leaf (_Hyoscyamus niger_, L.).
4. Tobacco leaf (_Nicotiana tabacum_, L.).]
SCHIZOGENOUS CAVITIES
=Schizogenous cavities= occur in white pine bark (Plate 62, Fig.
B). The cells lining the cavity are mostly tangentially elongated,
and the wall extends into the cavity in the form of a papillate
projection. Immediately back from these cells are two or three layers
of cells which resemble cortical parenchyma cells, except that they
are smaller and their walls are thinner.
In white pine bark there is a single layer of thin-walled cells
lining the cavity. Immediately surrounding the secretion cells is a
single layer of thick-walled fibrous cells.
In klip buchu (Plate 63, Fig. B), as in white pine leaf (Plate 64,
Fig. B), there is a single layer of thin-walled secretion cells which
are surrounded on three sides with parenchyma cells and on the outer
side by epidermal cells.
LYSIGENOUS CAVITIES
=Lysigenous cavities= occur on the rind of citrus fruits--bitter and
sweet orange, lemon, grapefruit, lime, etc., and in the leaves of
garden rue, etc.
In bitter orange peel, (Plate 64, Fig. A) the cavity is very
large, and the cells bordering the cavity are broken and partially
dissolved. The entire cells back of these are white, thin-walled,
tangentially elongated cells. There is a great variation in the size
of these cavities, the smaller cavities being the recently formed
cavities.
SCHIZO-LYSIGENOUS CAVITIES
=Schizo-lysigenous= cavities are formed in white pine bark and many
other plants owing to the increase in diameter of the stem. In such
cases the walls of the secreting cells break down. The resulting
cavity resembles lysigenous cavities.
=Unicellular secretion cavities= occur in ginger, aloe, calamus, and
in canella alba barb.
[Illustration: PLATE 62
_A._ Cross-section of calamus rhizome (_Acorus calamus_, L.). 1,
Intercellular space; 2, Parenchyma cells; 3, Secretion cavity.
_B._ Cross-section of white pine bark (_Pinus strobus_, L.). 1,
Parenchyma; 2, Secretion cavity; 3, Secretion cells.]
[Illustration: PLATE 63
_A._ Cross-section of a portion of canella alba bark (_Canella
alba_, Murr.). 1. Excretion cavity.
_B._ Cross-section of a portion of klip buchu leaf.
1. Epidermal cells.
2. Secretion cavity.
3. Secretion cells.]
[Illustration: PLATE 64
_A._ Cross-section of bitter orange peel (_Citrus aurantium_,
_amara_, L.). 1, Internal secretion cavity formed by the
dissolution of the walls of the central secreting cells; 2,
Secretion cells. _B._ Cross-section of white pine leaf (_Pinus
strobus_, L.). 1, Epidermal and hypodermal cells; 2, Parenchyma
cells with protruding inner walls; 3, Endodermis; 4, Secretion
cavity; 5, Secretion cells.]
In calamus (Plate 62, Fig. A) the cavity is larger than the
surrounding cells; it is rounded in outline, and it contains
oleoresin. These cavities are in contact with the ordinary parenchyma
cells, from which they are easily distinguished by their larger size
and rounded form.
The =unicellular oil cavity= of canella alba (Plate 63, Fig. A) is
rounded or oval in cross-section and is many times larger than the
surrounding cells. The wall, which is very thick, is of a yellowish
color.
Secretion cavities vary greatly in form, according to the part of the
plant in which they are found. In flower petals and leaves they are
spherical; in barks they are usually elliptical; in umbelliferous
fruits they are elongated and tube-like.
Mucilage cavities are not of common occurrence in medicinal plants.
They occur, however, in the stem and root bark of sassafras, the stem
bark of slippery elm, the root of althea, etc.
CHAPTER VIII
STORAGE TISSUE
Most drug plants contain storage products because they are
collected at a period of the year when the plant is storing, or has
stored, reserve products. These products are stored in a number of
characteristic ways and in different types of tissue.
The most important of the different types of storage tissue that
occurs in plants are the storage cells, the storage cavities, and the
storage walls.
STORAGE CELLS
Several different types of cells function as storage tissue. These
cells, which are given in the order of their importance, are
parenchyma, crystal cells, medullary rays, stone cells, wood fibres,
bast fibres, and epidermal and hypodermal cells.
CORTICAL PARENCHYMA
=Cortical parenchyma= of biennial rhizomes, bulbs, roots, and the
parenchyma of the endosperm of seeds store most of the reserve
economic food products of the higher plants.
=Pith parenchyma= of sarsaparilla root (Plate 65, Fig. 4) and
the pith parenchyma of the rhizome of memspermun, like the pith
parenchyma of most plants, function as storage cells.
WOOD PARENCHYMA
=Wood parenchyma=, particularly of the older wood, function as
storage tissue. The wood parenchyma of quassia, like the wood
parenchyma of most woods, contain stored products. In some cases the
wood parenchyma contain starch, in others crystals, and in others
coloring matter, etc.
[Illustration: PLATE 65
1. Stone cells with starch of Ceylon cinnamon (_Cinnamomum
ceylanicum_, Nees.). 2. Stone cells with solitary crystals of
calumba root (_Jateorhiza palmata_, [Lam.] Miers). 3. Parenchyma
cells, with starch of cascarilla bark (_Croton eluteria_, [L.]
Benn.). 4. Cortical parenchyma with starch of sarsaparilla root
(_Smilax officinalis_, Kunth). 5. Cortical parenchyma, with
starch of leptandra rhizome (_Leptandra virginica_, [L.] Nutt.).
6. Crystal cells, with solitary crystals of quebracho bark
(Schlechtendal). 7. Bast fibre of blackberry root with starch
(_Rubus cuneifolius_, Pursh.).]
[Illustration: PLATE 66
MUCILAGE AND RESIN
1. Cross-section of elm bark (_Ulmus fulva_, Michaux) showing two
cavities filled with partially swollen mucilage.
2. Mucilage mass from sassafras stem bark (_Sassafras variifolium_,
L.).
3. Mucilage mass from elm bark.
4. Resin mass from white pine bark (_Pinus strobus_, L.).]
In many plants, however, the parenchyma cells contain crystals. The
parenchyma cells of rhubarb contain rosette crystals, while the
parenchyma cells of the cortex of sarsaparilla and false unicorn root
contain bundles of raphides. In every case observed the raphides are
surrounded by mucilage. This is true of squills, sarsaparilla, false
unicorn, etc. When cells with raphides and mucilage are mounted in a
mixture of alcohol, glycerine, and water, the mucilage first swells
and finally disappears.
STORAGE CAVITIES
Particular attention should be given to =storage cavities= whenever
they occur in plants, for the reason that they are usually filled
with storage products, and for the added reason that storage cavities
are not common to all plants. Storage cavities occur in roots, stems,
leaves, flowers, fruits, and seeds.
CRYSTAL CAVITIES
Characteristic =crystal cavities= occur in many plants. Such a cavity
containing a bundle of raphides is shown in the cross-section of
skunk cabbage leaf (Plate 67).
SECRETION CAVITIES
In white pine bark there are a great number of secretion cavities
which are partially or completely filled with oleoresin. In the
cross-sections of white pine bark the secretion cavities are very
conspicuous, and they vary greatly in size. This variation is due,
first, to the age of the cavity, the more recently formed cavities
being smaller; and secondly, to the nature of the section, which will
be longer in longitudinal section, which will be through the length
of the secretion cavity, and shorter on transverse section. Such a
section shows the width of the secretion cavity.
Characteristic =mucilage cavities= occur in sassafras root, stem
bark, elm bark (Plate 66, Fig. 1), marshmallow root, etc. These
cavities form a conspicuous feature of the cross-section of these
plants. The presence or absence of mucilage cavities in a bark should
be carefully noted.
LATEX CAVITIES
The =latex tube cavities= are characteristic in the plants in which
they occur. These cavities as explained under latex tubes are very
irregular in outline.
[Illustration: PLATE 67
CROSS-SECTION OF SKUNK-CABBAGE LEAF (_Symplocarpus fœtidus_,
[L.] Nutt.)
1. Crystal cavity.
2. Bundle of raphides.]
OIL CAVITY
Canella alba contains an =oil cavity= resembling in form the mucilage
cavity of elm bark.
=Secretion cavities= occur in most of the umbelliferous fruits. For
each fruit there is a more or less constant number of cavities. Anise
has twenty or more, fennel usually has six cavities, and parsley has
six cavities.
In poison hemlock fruits there are no secretion cavities. In certain
cases, however, the number of secretion cavities can be made to vary.
This was proved by the author in the case of celery seed. He found
that cultivated celery seed, from which stalks are grown, contains
six oil cavities (Plate 122, Fig. 2), while wild celery seed (Plate
102, Fig. 1), grown for its medicinal value, always contains more
than six cavities. Most of the wild celery seeds contain twelve
cavities.
Many leaves contain cavities for storing secreted products. Such
storage cavities occur in fragrant goldenrod, buchu, thyme, savary,
etc.
The leaves in which such cavities occur are designated as
pellucid-punctate leaves. Such leaves will, when held between the eye
and the source of light, exhibit numerous rounded translucent spots,
or storage cavities.
GLANDULAR HAIRS
The =glandular hair of peppermint= (Plate 60, Fig. 3) and other mints
consists of eight secretion cells, arranged around a central cavity
and an outer wall which is free from the secretion cells. This outer
wall becomes greatly distended when the secretion cells are active,
and the space between the secretion cells and the wall serves as the
storage place for the oil. When the mints are collected and dried,
the oil remains in the storage cavity for a long time.
STONE CELLS
The =stone cells= of the different cinnamons (Plate 65, Fig. 1) store
starch grains; these grains often completely fill the stone cells.
The yellow stone cells of calumba root (Plate 65, Fig. 2) usually
contain four prisms of calcium oxalate, which may be nearly uniform
or very unequal in size.
BAST FIBRES
The =bast fibres= of the different rubus species (Plate 65, Fig. 7)
contain starch. The medullary rays of quassia (Plate 107, Fig. 2)
contain starch; while the medullary rays of canella alba contain
rosette crystals. In a cross-section of canella alba (Plate 81, Fig.
3) the crystals form parallel radiating lines which, upon closer
examination, are seen to be medullary rays, in each cell of which a
crystal usually occurs.
The =epidermal and hypodermal cells of leaves= serve as water-storage
tissue. These cells usually appear empty in a section.
The barks of many plants--_i.e._, quebracho, witch-hazel,
cascara, frangula, the leaves of senna and coca, and the root of
licorice--contain numerous crystals. These crystals occur in special
storage cells--=crystal cells= (Plate 65, Fig. 6)--which usually form
a completely enveloping layer around the bast fibres. These cells are
usually the smallest cells of the plant in which they occur, and with
but few exceptions each cell contains but a single crystal.
The epidermal cells of senna leaves and the epidermal cells of
mustard are filled with mucilage; the walls even consist of mucilage.
Such cells are always diagnostic in powders.
STORAGE WALLS
=Storage walls= (Plates 68 and 69) occur in colchicum seed, saw
palmetto seed, areca nut, nux vomica, and Saint Ignatius’s bean. In
each of these seeds the walls are strongly and characteristically
thickened and pitted. In no two plants are they alike, and in each
plant they are important diagnostic characters.
Storage cell walls consist of reserve cellulose, a form of cellulose
which is rendered soluble by ferments, and utilized as food during
the growth of the seed. Reserve cellulose is hard, bony, and of a
waxy lustre when dry. Upon boiling in water the walls swell and
become soft.
The structure of the reserve cellulose varies greatly in the
different seeds in which it occurs in the thickness of the walls and
in the number and character of the pores.
[Illustration: PLATE 68
RESERVE CELLULOSE
1. Saw palmetto (_Serenoa serrulata_, [Michaux] Hook., f.).
2. Areca nut (_Areca catechu_, L.).
3. Colchicum seed (_Colchicum autumnale_, L.).
3-_A_. Porous side wall.
3-_B_. Cell cavity above the side wall.]
[Illustration: PLATE 69
RESERVE CELLULOSE
1. Endosperm of nux vomica (_Strychnos nux vomica_, L.).
2. Endosperm of St. Ignatia bean (_Strychnos ignatii_, Berg.).]
CHAPTER IX
CELL CONTENTS
The cell contents of the plant are divided into two groups: first,
organic cell contents; and secondly, inorganic cell contents.
The =organic= cell contents include plastids, starch grains,
mucilage, inulin, sugar, hesperidin, alkaloids, glucocides, tannin,
resin, and oils.
CHLOROPHYLL
The =chloroplasts= of the higher plants are green, and they vary
somewhat in size, but they have a similar structure and form.
Chloroplasts are mostly oval in longitudinal view and rounded in
cross-section view. Each chlorophyll grain has an extremely thin
outer wall, which encloses the protoplasmic substance, the green
granules, a green pigment (chlorophyll), and a yellow pigment
(xanthophyll). Frequently the wall includes starch, oil drops, and
protein crystals.
Chloroplasts are arranged either in a regular peripheral manner along
the walls, or they are diffused throughout the protoplast.
The palisade cells of most leaves are packed with chlorophyll grains.
In the mesophyll cells the chlorophyll grains are not so numerous,
and they are arranged peripherally around the innermost part of the
wall.
Chloroplasts multiply by fission--that is, each chloroplast divides
into two equal halves, each of which develops into a normal
chloroplast.
Chlorophyll occurs in the palisade, spongy parenchyma, and guard
cells of the leaf; in the collenchyma and parenchyma of the cortex
of the stems of herbs and of young woody stems, and, under certain
conditions, in rhizomes and roots exposed to light. Almost without
exception young seeds and fruits have chlorophyll.
In powdered leaves, stems, etc., the chlorophyll grains occur in the
cells as greenish, more or less structureless masses. Yet cells with
chlorophyll are readily distinguished from cells with other cell
contents. In witch-hazel leaf the chlorophyll grains appear brownish
in color. Powdered leaves and herbs are readily distinguished from
bark, wood, root, and flower powders.
Leaves and the stems of herbs are of a bright-green color. With the
exception of the guard cells, the chloroplasts occur one or more
layers below the epidermis; but, owing to the translucent nature of
the outer walls of these cells, the outer cells of leaves and stems
appear green.
Wild cherry, sweet birch, and, in fact, most trees with smooth barks
have =chloroplasts= in several of the outer layers of the cortical
parenchyma. When the thin outer bark is removed from these plants,
the underlying layers are seen to be of a bright-green color.
LEUCOPLASTIDS
=Leucoplastids=, or colorless plastids, occur in the underground
portions of the plant; they may, when these organs in which they
occur are exposed to light, change to chloroplastids.
Leucoplasts are the builders of starch grains. They take the chemical
substance starch and build or mould it into starch grains, storage
starch, or reserve starch.
Other characteristic chromoplasts found in plants are yellow and
red. Yellow chromoplasts occur in carrot root and nasturtium flower
petals. Red plastids occur in the ripe fruit of capsicum.
STARCH GRAINS
The chemical substance starch (C₆H₁₀O₅) is formed in chloroplasts.
The starch thus formed is removed from the chloroplasts to other
parts of the plant because it is the function of the chloroplasts to
manufacture and not to store starch.
The starch formed by the chloroplasts is acted upon by a ferment
which adds one molecule of water to C₆H₁₀O₅, thus forming sugar
C₆H₁₂O₆. This sugar is readily soluble in the cell sap, and is
conducted to all parts of the plant. The sugar not utilized in cell
metabolism is stored away in the form of reserve starch or starch
grains by colorless plastids or amyloplasts.
The amyloplasts change the sugar into starch by extracting a molecule
of water. This structureless material (starch) is then formed by the
amyloplast into starch grains having a definite and characteristic
form and structure.
Starch grams vary greatly in different species of plants, owing
probably to the variation of the chemical composition, density, etc.,
of the protoplast, and to the environmental conditions under which
the plant is growing.
OCCURRENCE
Starch grains are simple, compound, or aggregate. =Simple starch=
grains may occur as isolated grains (Plates 70, 71, and 72), or they
may be associated as in cardamon seed, white pepper, cubeb, and
grains of paradise, where the simple grains stick together in masses,
having the outline of the cells in which they occur. These masses are
known as aggregate starch.
=Aggregate starch= (Plate 76) varies greatly in size, form, and in
the nature of the starch grains forming the aggregations.
=Compound starch grains= may be composed of two or more parts, and
they are designated as 2, 3, 4, 5, etc., compound (Plate 75).
The parts of a compound grain may be of equal size (Plate 75, Fig.
4), or they may be of unequal size (Plate 75, Fig. 2).
In most powders large numbers of the parts of the compound grains
become separated. The part in contact with other grains shows plane
surfaces, while the external part of the grain has a curved surface.
There will be one plane and one curved surface if the grain is a half
of a two-compound grain; two plane and one curved surface if the
grain is a part of a three-compound grain, etc.
The simple starch grains forming the aggregations become separated
during the milling process and occur singly, so that in the drugs
cited above the starch grains are solitary and aggregate.
Many plants contain both simple and compound starch grains (Plate 74,
Fig. 3).
In some forms--_e.g._, belladonna root (Plate 75, Fig. 2) the
compound grains are more numerous; while in sanguinaria the simple
grains are more numerous, etc.
OUTLINE
The =outline= of starch grains is made up of (1) rounded, (2) angled,
and (3) rounded and angled surfaces.
Starch grains with rounded surfaces may be either spherical, as in
Plate 74, Fig. 3, or oblong or elongated, as in Plate 71, Fig. 1.
Other starches with rounded surfaces are shown on Plates 72 and 73.
Angled outlined grains are common to cardamon seed, white pepper,
cubebs, grains of paradise (Plate 76, Fig. 4), and to corn (Plate 70,
Fig. 3).
The outlines of all compound grains are made up partly of plane and
partly of curved surfaces.
SIZE
The =size= (greatest diameter) of starch varies greatly even in the
same species, but for each plant there is a normal variation.
In spherical starch grains the size of the individual grains is
invariable, but in elongated starch grains and in parts of compound
grains the size will vary according to the part of the grain
measured. In zedoary starch (Plate 71, Fig. 4), for instance, the
size will vary according to whether the end, side, or surface of the
starch grain is in focus.
The parts of compound grains often vary greatly in size. Such a
variation is shown in Plate 75, Fig. 2.
HILUM
The =hilum= is the starting-point of the starch grain or the first
part of the grain laid down by the amyloplast. The hilum will be
central if formed in the middle of the amyloplast, and excentral if
formed near the surface of the amyloplast. It has been shown that the
developing starch grain with eccentric hilum usually extends the wall
of the amyloplast if it does not actually break through the wall.
Starch grains with excentral hilums are therefore longer than broad.
[Illustration: PLATE 70
STARCH
1. Calabar bean (_Physostigma venenosum_, Balfour).
2. Marshmallow root (_Althæa officinalis_, L.).
3. Field corn (_Zea mays_, L.).]
[Illustration: PLATE 71
STARCH
1. Galanga root (_Alpinia officinarum_, Hance). 2. Kola nut (_Cola
vera_, [K.] Schum.). 3. Geranium rhizome (_Geranium maculatum_ L.).
4. Zedoary root (_Curcuma zedoaria_, Rosc.). 4-_A_. Surface view of
starch grain. 4-_B_. Side view of starch grain. 4-_C_. End view of
starch grain.]
In central hilum starch grains the grain is laid down around the
hilum in the form of concentric layers. These layers are of variable
density. The dense layers are formed when plenty of sugar is
available, and the less dense layers are formed when little sugar
is available. The unequal density of the different layers gives the
striated appearance characteristic of so many starch grains.
In eccentric hilum starch grains the starch will be deposited in
layers which are outside of and successively farther from the hilum.
The term _hilum_ has come to have a broader meaning than formerly.
Hilum includes at the present time not only the starting-point of the
starch grain, but the fissures which form in the grain upon drying.
In all cases these fissures originate in the starting-point, hilum,
and in some cases extend for some distance from it. The hilum, when
excentral, may occur in the broad end of the grain, galanga, and
geranium (Plate 71, Figs, 1 and 3), or in the narrow end of the
grain, zedoary (Plate 71, Fig. 4).
NATURE OF THE HILUM
The hilum, whether central or excentral, may be rounded (Plate 75,
Fig. 1); or simple cleft, which may be straight (Plate 71, Fig. 1);
or curved cleft (Plate 71, Fig. 2); or the hilum may be a multiple
cleft (Plate 74, Fig. 3).
In studying starches use cold water as the mounting medium, because
in cold water the form and structure are best shown, and because
there is no chemical action on the starch. On the other hand, the
form and structure will vary considerably if the starch is mounted
in hot water or in solutions of alkalies or acids. The hilum appears
colorless when in sharp focus, and black when out of focus.
Starch grains, when boiled with water, swell up and finally
disintegrate to form starch paste.
Starch paste turns blue upon the addition of a few drops of weak
Lugol solution. Upon heating, this blue solution is decolorized, but
the color reappears upon cooling. If a strong solution of Lugol is
used in testing, the color will be bluish black.
[Illustration: PLATE 72
STARCH
1. Orris root (_Iris florentinia_ L.).
2. Stillingia root (_Stillingia sylvatica_, L.).
3. Calumba root (_Jateorhiza palmata_, [Lam.] Miers.).]
[Illustration: PLATE 73
STARCH
1. Male fern (_Dryopteris marginalis_, [L.] A. Gray).
2. African ginger (_Zingiber officinalis_, Rosc.).
3. Yellow dock (_Rumex crispus_, L.).
4. Pleurisy root (_Asclepias tuberosa_, L.).]
[Illustration: PLATE 74
STARCH
1. Kava-kava (_Piper methysticum_, Forst., f.).
2. Pokeroot (_Phytolacca americana_, L.).
3. Rhubarb (_Rheum officinale_, Baill.).]
[Illustration: PLATE 75
STARCH GRAINS
1. Bryonia (_Bryonia alba_, L.).
2. Belladonna root (_Atropa belladonna_, L.).
3. Valerian root (_Valeriana officinalis_, L.).
4. Colchicum root (_Colchicum autumnale_, L.).]
[Illustration: PLATE 76
STARCH MASSES
1. Aggregate starch of cardamon seed (_Elettaria cardamomum_,
Maton).
2. Aggregate starch of white pepper (_Piper nigrum_, L.).
3. Aggregate starch of cubebs (_Piper cubeba_, L., f.).
4. Aggregate starch of grains of paradise (_Amomum melegueta_,
Rosc.).]
INULIN
=Inulin= is the reserve carbohydrate material found in the plants of
the composite family.
The medicinal plants containing inulin are dandelion, chicory,
elecampane, pyrethrum, and burdock. Plate 77, Figs, 1 and 2 show
masses of inulin in dandelion and pyrethrum.
In these plants the inulin occurs in the form of irregular,
structureless, grayish-white masses (Plate 77). In powdered drugs
inulin occurs either in the parenchyma cell or as irregular isolated
fragments of variable size and form. Inulin is structureless and the
inulin from one plant cannot be distinguished microscopically from
the inulin of another plant. For this reason inulin has little or no
diagnostic value. The presence or absence of inulin should always be
noted, however, in examining powdered drugs, because only a few drugs
contain inulin.
When cold water is added to a powder containing inulin it dissolves.
Solution will take place more quickly, however, in hot water.
Inulin occurs in the living plant in the form of cell sap. If fresh
sections of the plant are placed in alcohol or glycerine, the inulin
precipitates in the form of crystals.
MUCILAGE
=Mucilage= is of common occurrence in medicinal plants.
Characteristic mucilage cavities filled with mucilage occur in
sassafras stem (Plate 66, Fig. 2), in elm bark (Plate 66, Fig. 1), in
althea root, in the outer layer of mustard seed, and in the stem of
cactus grandiflorus. In addition, mucilage is found associated with
raphides in the crystal cells of sarsaparilla, squill, false unicorn,
and polygonatum.
When drugs containing mucilage are added to alcohol, glycerine, and
water mixture, the mucilage swells slightly and becomes distinctly
striated, but it will not dissolve for a long time. Refer to Plate
79, Fig. 6.
Mucilage, when associated with raphides, swells and rapidly dissolves
when added to alcohol, glycerine, and water mixture. The mucilage is,
therefore, different from the mucilage found in mucilage cavities,
because it is more readily soluble.
[Illustration: PLATE 77
INULIN (_Inula helenium_, L.)
1. Inulin in the parenchyma cells of dandelion root.
2. Inulin from Roman pyrethrum root (_Anacyclus pyrethrum_, [L.] D.
C.). ]
In coarse-powdered bark and other mucilage containing drugs the
mucilage masses are mostly spherical or oval in outline (Plate 66,
Figs. 2 and 3) the form being similar to the cavity in which the mass
occurs.
Acacia, tragacanth, and India gum consist of the dried mucilaginous
excretions.
HESPERIDIN
=Hesperidin= occurs in the epidermal cells of short and long buchu.
It is particularly characteristic in the epidermal cells of the dried
leaves of short buchu. In these leaves the hesperidin occurs in
masses which resemble rosette crystals (Plate 54, Fig. 1).
Hesperidin is insoluble in glycerine, alcohol, and water, but it
dissolves in alkali hydroxides, forming a yellowish solution.
VOLATILE OILS
=Volatile oils= occur in cinnamon stem bark, sassafras root bark,
flowers of cloves, and in the fruits of allspice, anise, fennel,
caraway, coriander, and cumin.
In none of these cases is the volatile oil diagnostic, but its
presence must always be determined.
When a powdered drug containing a volatile oil is placed in alcohol,
glycerine, and water mixture the volatile oil contained in the
tissues will accumulate at the broken end of the cells in the form of
rounded globules, while the volatile oil adhering to the surface of
the fragments will dissolve in the mixture and float in the solution
near the under side of the cover glass. Volatile oil is of little
importance in histological work.
TANNIN
=Tannin= masses are usually red or reddish brown. Tannin occurs in
cork cells, medullary rays of white pine bark (Plate 48, Fig. B),
stone cells, and in special tannin sacs.
The stone cells of hemlock and tamarac bark and the medullary rays of
white pine and hemlock bark contain tannin.
Tannin associated with prisms occurs in tannin sacs in white pine and
tamarac bark. These sacs are frequently several millimeters in length
and contain a great number of crystals surrounded by tannin.
Deposits of tannin are colored bluish black with a solution of ferric
chloride.
ALEURONE GRAINS
=Aleurone grains= are small granules of variable structure, size,
and form, and they are composed of reserve proteins. They occur in
celery, fennel, coriander, and anise, fruits, in sesame, sunflower,
curcas, castor oil, croton oil, bitter almond, and other oil seeds.
In many of the seeds the aleurone grains completely fill the cells of
the endosperm, embryo, and perisperm. In wheat, rye, barley, oats,
and corn the aleurone grains occur only in the outer layer or layers
of the endosperm, the remaining layers in these cases being filled
with starch.
In powdered drugs the aleurone grains occur in parenchyma cells or
free in the field.
STRUCTURE OF ALEURONE GRAINS
Aleurone grains are very variable in structure. The simplest grains
consist of an undifferentiated mass of proteid substance surrounded
by a thin outer membrane. In other grains the proteid substance
encloses one or more rounded denser proteid bodies known as globoids.
In other grains a crystalloid--crystal-like proteid substance--is
present in addition to the globoid. In some grains are crystals
of calcium oxalate, which may occur as prisms or as rosettes. All
the different parts, however, do not occur in any one grain. In
castor-oil seed (Plate 77_a_, Fig. 8) are shown the membrane (_A_),
the ground mass (_B_), the crystalloid (_C_), and the globoid (_D_).
FORM OF ALEURONE GRAINS
Much attention has been given to the study of the special parts
of the aleurone grains, but one of the most important diagnostic
characters has been overlooked, namely, that of comparative form. For
the purposes of comparing the forms of different grains, they should
be mounted in a medium in which the grain and its various parts are
insoluble. Oil of cedar is such a medium. The variation in form and
size of the aleurone grains when mounted in oil of cedar is shown in
Plate 77_a_.
DESCRIPTION OF ALEURONE GRAINS
The aleurone grains of curcas (Plate 77_a_, Fig. 1) vary in form
from circular to lens-shaped, and each grain contains one or more
globoids. The globoids are larger when they occur singly. In
sunflower seed (Plate 77_a_, Fig. 2) the grains vary from reniform to
oval, and one or more globoids are present; many occur in the center
of the grain.
The aleurone grains of flaxseed (Plate 77_a_, Fig. 3) resemble in
form those of sunflower seed, but the grains are uniformly larger and
some of the grains contain as many as five globoids.
In bitter almond (Plate 77_a_, Fig. 4) the aleurone grains are mostly
circular, but a few are nearly lens-shaped. A few of the large,
rounded grains contain as many as nine globoids; in such cases one
of the globoids is likely to be larger than the others. The aleurone
grains of croton-oil seed (Plate 77_a_, Fig. 5) are circular in
outline, variable in form, and each grain contains from one to seven
globoids.
In sesame seed (Plate 77_a_, Fig. 6) the typical grain is angled in
outline and the large globoid occurs in the narrow or constricted end.
The aleurone grains of castor-oil seed (Plate 77_a_, Fig. 7) resemble
those of sesame seed, but they are much larger, and many of the
grains contain three large globoids. When these grains are mounted in
sodium-phosphate solution, the crystalloid becomes visible.
TESTS FOR ALEURONE GRAINS
Aleurone grains are colored yellow with nitric acid and red with
Millon’s reagent.
The proteid substance of the mass of the grain, of the globoid, and
of the crystalloid, reacts differently with different reagents and
dyes.
The ground substance and the crystalloids are soluble in dilute
alkali, while the globoids are insoluble in dilute alkali.
The ground substance and crystalloids are soluble in sodium
phosphate, while the globoids are insoluble in sodium phosphate.
Calcium oxalate is insoluble in alkali and acetic acid, but it
dissolves in hydrochloric acid.
[Illustration: PLATE 77_a_
ALEURONE GRAINS
1. Curcas (_Jatropha curcas_, L.).
2. Sunflower seed (_Helianthus annuus_, L.).
3. Flaxseed (_Linum usitatissimum_, L.).
4. Bitter almond (_Prunus amygdalus_, _amara_, D.C.).
5. Croton-oil seed (_Croton tiglium_, L.).
6. Sesame seed (_Sesamum indicum_, L.).
7 and 8. Castor-oil seed (_Ricinus communis_, L.).]
CRYSTALS
Calcium oxalate crystals form one of the most important inorganic
cell contents found in plants, because of the permanency of the
crystals, and because the forms common to a given species are
invariable. By means of calcium oxalate crystals it is possible to
distinguish between different species. In butternut root bark, for
instance, only rosette crystals are found, while in black walnut
root bark--a common substitute for butternut bark--both prisms and
rosettes occur. This is only one of the many examples which could be
cited.
These crystals, for purposes of study, will be grouped into four
principal classes, depending upon form and not upon crystal system.
These classes are micro-crystals, raphides, rosettes, and solitary
crystals.
MICRO-CRYSTALS
=Micro-crystals= are the smallest of all the crystals. Under the
high power of the microscope they appear as a V, a Y, an X, and as
a T. They are, therefore, three- or four-angled (Plate 78). The
thicker portions of these crystals are the parts usually seen, but
when a close observation of the crystals is made the thin portions
of the crystal connecting the thicker parts may also be observed.
Micro-crystals should be studied with the diaphragm of the microscope
nearly closed and with the high-power objective in position. While
observing the micro-crystals, raise and lower the objective by the
fine adjustment in order to bring out the structure of the crystal
more clearly. Micro-crystals occur in parenchyma cells of belladonna,
scopola, stramonium, and bittersweet leaves; in belladonna, in
horse-nettle root, in scopola rhizome, in bittersweet stems, and in
yellow and red cinchona bark, etc.
The crystals in each of the above parts of the plant are similar in
form, the only observed variation being that of size. Their presence
or absence should always be noted when studying powders.
RAPHIDES
=Raphides=, which are usually seen in longitudinal view, resemble
double-pointed needles. They are circular in cross-section, and the
largest diameter is at the centre, from which they taper gradually
toward either end to a sharp point.
[Illustration: PLATE 78
MICRO-CRYSTALS
1. Horse-nettle root (_Solanum carolinense_, L.).
2. Scopola rhizome (_Scopolia carniolica_, Jacq.).
3. Belladonna root (_Atropa belladonna_, L.).
4. Bittersweet stem (_Solanum dulcamara_, L.).
5. Scopola leaf (_Scopola carniolica_, Jacq.).
6. Tobacco leaf (_Nicotiana tabacum_, L.).
7. Belladonna leaf (_Atropa belladonna_, L.).]
Raphides occur in bundles, as in false unicorn root (Plate 79, Figs.
6, A, B, and C), rarely as solitary crystals.
In ipecac root the crystals are usually solitary. In sarsaparilla
root, squill, etc., the raphides occur both in clusters, part of
bundle, or in bundles, and as solitary crystals.
In most drugs the crystals are entire; but in squills, where the
raphides are very large, they are broken. In phytolacca (Plate 79,
Fig. 1) and in hydrangea the raphides are usually broken, owing to
the fact that these drugs contain large quantities of fibres which
break them up into fragments when the drug is milled.
There is the greatest possible variation in the size of raphides in
the same and in different drugs, but the larger forms are constant in
the same species.
Raphides are deposited in parenchyma cells and in special raphides
sacs. These crystals are always surrounded with mucilage.
ROSETTE CRYSTALS
=Rosette crystals= are compound crystals composed of an aggregation
of small crystals arranged in a radiating manner around a central
core. This core appears nearly black, and the whole mass is nearly
spherical. The free ends of the crystals are sharp-pointed or blunt.
Characteristic rosette crystals occur in frangula bark, spikenard
root, wahoo stem, root bark, rhubarb, etc. (Plate 80, Figs. 1, 2, 3,
4, 5, and 6).
These crystals are very variable in size. This variation is
illustrated by the crystals of Plate 80.
Usually there is a variation in size of the crystals occurring in
a given plant, but for each plant there is a more or less uniform
variation. For instance, the largest rosette crystal occurring in
wahoo root bark (Plate 80, Fig. 5) is smaller than the largest
crystal occurring in rhubarb (Plate 80, Fig. 6), etc.
[Illustration: PLATE 79
RAPHIDES
1. Phytolacca root (_Phytolacca americana_, L.). 2. Squills
(_Urginea maritima_ [L.] Baker). 3. Hydrangea root (_Hydrangea
arborescens_, L.). 4. Convallaria (_Convallaria majalis_, L.).
5. Carthagean ipecac (_Cephælis acuminata_ Karst.) 6. Bundle of
raphides from false unicorn root.
_A._ Bundle surrounded with mucilage. _B._ Mucilage expanded and
partially dissolved. _C._ Bundle free of mucilage.]
[Illustration: PLATE 80
ROSETTE CRYSTALS
1. Frangula bark (_Rhamnus frangula_, L.).
2. White oak bark (_Quercus alba_, L.).
3. Spikenard root (_Aralia racemosa_, L.).
4. Wahoo stem bark (_Euonymus atropurpureus_, Jacq.).
5. Wahoo root bark (_Euonymus atropurpureus_, Jacq.).
6. Rhubarb (_Rheum officinale_, Baill.).]
The prisms forming the rosette crystals, like all prisms, decompose
white light, with the result that rosette crystals frequently appear
variously colored. Rhubarb crystals, for instance, are blue or
violet. Most of the smaller rosette crystals, however, appear grayish
white with a darker-colored centre.
Rosette crystals occur in parenchyma cells (Plate 81, Fig. 4) and in
medullary rays (Plate 81, Fig. 3).
SOLITARY CRYSTALS
=Solitary crystals= are the most variable of all the forms of calcium
oxalate. They usually occur in crystal cells associated with bast
fibres and stone cells, less frequently in stone cells (Plate 33,
Fig. 2). There are many different and characteristic forms of prisms.
The more common are:
1. Rectangular:
A. Parallelepipeds.
B. Cubes.
2. Polyhedrons:
A. Irregular polyhedrons.
I. Flat bases.
(_a_) Non-notched.
(_b_) Notched.
II. Tapering bases.
B. Octohedrons.
The crystals occurring in Batavia cinnamon and henbane leaves are
parallelopipeds (Plate 82, Figs. 1 and 2).
The crystals occurring in cactus grandiflorus, hemlock bark, krameria
root, and soap bark are irregular polyhedrons (Plate 83). They
are longer than broad, and the ends are tapering. The crystal of
cactus grandiflorus has the narrowest diameter of these four, while
the crystals of soap bark have the widest diameter. In coca leaf,
xanthoxylum bark, elm bark, Spanish licorice, and in white oak (Plate
84), and in cocillina bark (Plate 82, Fig. 4) the crystals are all
irregular polyhedrons with flat bases. They are mostly longer than
broad and they are all widest in the centre; in each a few crystals
are notched, but most of the crystals are not notched.
The crystals in quassia wood, uva-ursi leaf, and most of those of
quebracho and wild cherry bark (Plate 86, Figs. 1, 2, 3, and 4) are
irregular polyhedrons with flat ends. They are longer than broad,
widest at the centre, and non-notched.
[Illustration: PLATE 81
INCLOSED ROSETTE CRYSTALS
1. Hops (_Humulus lupulus_, L.).
2. Bracts of cannabis indica (_Cannabis sativa_, variety _Indica_,
Lamarck).
3. Medullary rays of canella alba.
4. Parenchyma cells of mandrake (_Podophyllum peltatum_, L.).]
[Illustration: PLATE 82
SOLITARY CRYSTAL
1. Batavia cinnamon (_Cinnamomum burmanni_, Nees).
2. Henbane leaves (_Hyoscyamus niger_, L.).
3. Morea nutgalls.
4. Cocillana bark (_Guarea rusbyi_ [Britton], Rusby).]
[Illustration: PLATE 83
SOLITARY CRYSTALS
1. Cactus grandiflorus (_Cereus grandiflorus_ [L.], Britton and
Rose).
2. Hemlock bark (_Tsuga canadensis_ [L.], Carr.).
3. Krameria root (_Krameria triandra_, Ruiz and Pav.).
4. Soapbark (_Quillaja saponaria_, Molina).]
[Illustration: PLATE 84
SOLITARY CRYSTALS
1. Coca leaf (_Erythroxylon coca_, Lamarck).
2. Xanthoxylum bark (_Zanthoxylum americanum_, Miller).
3. Elm bark (_Ulmus fulva_, Michaux).
4. Spanish licorice root (_Glycyrrhiza glabra_, L.).
5. White oak bark (_Quercus alba_, L.).]
Cubes occur in senna, cascara sagrada, frangula, white pine, tamarac
(Plate 85), quassia, uva-ursi, quebracho, and in wild cherry (Plate
86).
The crystals of morea nutgalls (Plate 82, Fig. 3) are octahedrons,
and they resemble the crystals of calcium oxalate found in urinary
sediments.
While studying the prisms, focus first on the upper surface and then
down to the under surface in order to observe the forms accurately.
There are several plants in which more than one form of crystal
occur. Rosette crystals and prisms are associated, for instance, in
cascara sagrada, frangula, condurango, dogwood, and pleurisy root
(Plate 87, Figs. 1, 2, 3, 4, and 5).
An important factor to be kept in mind in studying crystals is the
number--whether abundant, as in rhubarb, or sparingly present, as in
mandrake, etc. Variation in the number of crystals is not uncommon,
even in different parts of the same plants. In wahoo stem bark, for
instance, there are several times as many rosette crystals as there
are in the root bark.
Crystals of calcium oxalate are freely soluble in dilute hydrochloric
acid without effervescence; but they are insoluble in acetic acid and
in sodium and potassium hydroxide solutions. With sulphuric acid they
form crystals of calcium sulphate.
CYSTOLITHS
=Cystoliths= consist of calcium carbonate deposited over and around a
framework of cellulose.
FORMS OF CYSTOLITHS
The =forms of cystoliths= differ greatly in the different plants in
which they occur.
In the rubber-plant leaf, the cystolith resembles a bunch of grapes
and is stalked; in ruellia root (Plate 87, Fig. 1) the cystoliths
vary from nearly circular to narrowly cylindrical, and no stalk is
present; also the cystolith nearly fills the cell in which it occurs.
In the hair of cannabis indica (Plate 88, Fig. 3), the cystolith
varies in form according to the size and shape of the hair, but in
all the hairs the cystolith appears to be attached to the upper
curved part of the inner wall of the hair.
[Illustration: PLATE 85
SOLITARY CRYSTALS
1. India senna (_Cassia angustifolia_, Vahl.).
2. Cascara sagrada bark (_Rhamnus purshiana_, D. C.).
3. Frangula bark (_Rhamnus frangula_, L.).
4. White pine bark (_Pinus strobus_, L.).
5. Tamarac bark (_Larix laricina_ [Du Roi], Koch).]
[Illustration: PLATE 86
SOLITARY CRYSTALS
1. Quassia (_Picræna excelsa_ [Swartz.], Lindl.).
2. Uva-ursi leaf (_Arctostaphylos uva-ursi_ [L.], Spring.).
3. Quebracho bark (_Aspidosperma quebracho-blanco_, Schlechtendal).
4. Wild-cherry bark (_Prunus serotina_, Ehrh.).]
[Illustration: PLATE 87
ROSETTE CRYSTALS AND SOLITARY CRYSTALS OCCURRING IN
1. Cascara sagrada bark (_Rhamnus purshiana_, D.C.).
2. Frangula bark (_Rhamnus frangula_, L.).
3. Cundurango bark (_Marsdenia cundurango_, [Triana] Nichols).
4. Dogwood root bark (_Cornus florida_, L.).
5. Pleurisy root (_Asclepias tuberosa_, L.).]
[Illustration: PLATE 88
CYSTOLITHS
1. Ruellia root (_Ruellia ciliosa_, Pursh.).
2. Pellionia leaf.
3. Cannabis indica (_Cannabis sativa_, variety _Indica_, Lam.).]
Cystoliths occur, then, in special cavities, in parenchyma
cells (rubber-plant leaf, fig, pellionea, and mulberry), and in
non-glandular hairs (cannabis indica).
In powdered ruellia root the cystoliths occur in or are separated
from the parenchyma cells.
TESTS FOR CYSTOLITHS
When dilute hydrochloric acid or acetic acid is added to cystoliths a
brisk effervescence takes place with the evolution of carbon dioxide
gas.
Part III
HISTOLOGY OF ROOTS, RHIZOMES, STEMS,
BARKS, WOODS, FLOWERS, FRUITS,
AND SEEDS
In Part II the different types of cells and cell contents found in
plants have been studied. In Part III it will be shown how these
different cells are associated and the nature of the cell contents
in the different parts of the plant. These parts are the root, the
rhizome, the stem of herbs, bark and wood of woody stems, the leaf,
the flower, the fruit, and the seed.
CHAPTER I
ROOTS AND RHIZOMES
Some fifty-five roots, rhizomes, and rhizomes and roots are official
in the pharmacopœia and national formulary. About 5 of these are
obtained from monocotyledonous plants, and 50 from dicotyledonous
plants.
In studying the structure of roots and rhizomes, then, it must first
be determined whether the root in question is monocotyledonous or
dicotyledonous. This fact is ascertained by determining the type of
the fibro-vascular bundle. The bundle is of the open collateral type
in all rhizomes and roots obtained from monocotyledonous plants, but
it is closed, radial, or concentric in the monocotyledonous type.
In both of these groups the cellular plan of structure is similar,
the chief variation being the absence of one or more types of cells,
the variation in the amount, in arrangement, in the anatomical
structure, in the color, and in the cell contents of the individual
cells. These facts will be impressed on the mind while studying the
rhizomes and the roots.
CROSS-SECTION PINK ROOT
The cross-section of pink root (Plate 89) has the following structure:
=Epidermis.= The epidermal cells are small, nearly as long as broad,
and the outer wall is thicker and darker in color than the side and
inner walls. The cells usually contain air.
=Cortex.= The cortical parenchyma cells are very large and somewhat
rounded in outline, and the walls are white. There are about twelve
rows of these cells, and each cell contains numerous small, rounded
starch grains.
=Endodermis.= The endodermal cells are tangentially elongated, and
the walls are very thin and white. There are two or three layers of
endodermal cells; the cells’ outer layers are larger than the cells
of the inner layers.
[Illustration: PLATE 89
CROSS-SECTION OF ROOT OF SPIGELIA MARYLANDICA, L.
1. Epidermis. 2. Cortical parenchyma. 2´. Intercellular space. 3.
Endodermis. 4. Pericycle. 5. Cambium. 6. Xylem. 7. Pith.]
=Pericycle.= The cells forming the pericycle are sieve cells and
phloem parenchyma. The =sieve cells= are small, angled cells with
extremely thin, white walls.
The =phloem parenchyma= resemble the sieve cells, except that they
are larger.
=Cambium.= The cambium cells are rectangular in shape; the walls are
thin and white.
=Xylem.= The xylem is composed of tracheids, wood parenchyma, and
wood fibres.
=Tracheids.= The tracheids are the largest diameter cells of the
centre of the root. The walls are thick and the cells are slightly
angled in outline.
=Wood Parenchyma.= The wood parenchyma cells surrounding the
tracheids are five to seven, angled, and the walls are not so thick
as the walls of the tracheids.
=Medullary Rays.= The medullary ray cells resemble the structure of
the wood parenchyma cells, but they are radially elongated.
=Pith Parenchyma.= The cells forming the pith parenchyma are larger
than the cells of wood parenchyma, but their structure is similar.
CROSS-SECTION RUELLIA ROOT
The cross-section of ruellia root (Plate 90) shows the following
structure. It should be carefully noted how the structure differs
from that of pink root:
=Epidermis.= The epidermal cells are angled and variable in size;
many of the epidermal cells are modified as root hairs.
=Hypodermis.= The cells of the hypodermis are one layer in thickness
and their structure is similar to the epidermal cells.
=Cortex.= The cortex contains parenchyma and stone cells. The outer
layers of the cortical parenchyma cells are round in outline, and
they contain dark-brown cell contents, while the cortical parenchyma
cells bordering on the endodermis are small and they are free of
dark-brown contents.
Many of the inner parenchyma cells contain amorphous deposits of
calcium carbonate.
[Illustration: PLATE 90
RUELLIA ROOT (_Ruellia ciliosa_, Pursh.).
1. Epidermis with root hair. 2. Parenchyma cells with dark
contents. 3. Sclerid. 4. Parenchyma without dark cell contents. 5.
Endodermis. 6. Bast fibers and phloem. 7. Cambium. 8. Xylem. 10.
Pith.]
The =stone cells= are porous and striated, and the walls are thick
and white.
=Endodermis.= The endodermal cells are tangentially elongated, and
the walls are thin and white.
=Pericycle.= The cells forming the pericycle are the sieve cells,
bast fibres, and phloem parenchyma.
The =sieve cells= are small, angled cells with thin, white walls.
The =phloem parenchyma= cells resemble the sieve cells, but they are
larger.
The =bast fibres= occur singly or in groups of two or three. They
are rounded in outline, and the walls are white, non-porous, and
non-striated.
=Xylem.= The xylem is composed of vessels, wood parenchyma, and wood
fibres.
=Vessels.= The vessels are rounded in outline and few in number.
=Wood Parenchyma.= The wood parenchyma cells are variable in size and
shape, but all the cells are angled in outline.
=Medullary Rays.= The medullary ray cells are not clearly
distinguishable.
=Pith Parenchyma.= The pith parenchyma cells of the centre of the
root resemble the cortical parenchyma cells.
That the structure of rhizomes is similar to the structure of roots
is shown by the drawings of spigelia rhizome (Plate 91), and by
ruellia rhizome (Plate 92).
CROSS-SECTION SPIGELIA RHIZOME
The cross-section of spigelia rhizome (Plate 91) is as follows:
=Epidermis.= The epidermal cells are nearly angled and free of cell
contents.
=Cortex.= The cortical parenchyma cells are usually slightly
tangentially elongated. The cells of the outer layers are larger than
the cells of the inner layers.
=Phloem.= The phloem contains sieve cells and phloem parenchyma. The
sieve cells are small, angled cells with thin, white walls.
The phloem parenchyma cells resemble the sieve cells, but they are
larger.
[Illustration: PLATE 91
CROSS-SECTION OF RHIZOME OF SPIGELIA MARYLANDICA, L.
1. Epidermis. 2. Cortical parenchyma. 3. Phloem. 4. Cambium. 5.
Xylem. 6. Internal phloem. 7. Pith with starch.]
[Illustration: PLATE 92
CROSS-SECTION OF RHIZOME OF RUELLIA CILIOSA, Pursh.
1. Epidermis. 2. Cystolith. 3. Stone cell. 4. Cortical parenchyma.
5. Bast fibres. 6. Pericycle. 7. Xylem. 8. Pith.]
=Cambium.= The cambium cells are rectangular, and they are usually
not clearly seen because the walls are partially collapsed.
=Xylem.= The xylem is composed of vessels, wood parenchyma, medullary
rays, and pith parenchyma.
=Vessels.= The vessels are slightly angled in outline and few in
number.
=Wood Parenchyma.= The wood parenchyma cells are small and angled.
=Medullary Rays.= The medullary ray cells are tangentially elongated,
but in structure resemble the wood parenchyma cells.
=Pith Parenchyma.= The pith parenchyma cells are rounded in outline
and contain small, simple, rounded starch grains.
CROSS-SECTION RUELLIA RHIZOME
The cross-section of ruellia rhizome (Plate 92) differs from the
structure of spigelia rhizome. It is as follows:
=Epidermis.= The epidermal cells vary in shape from nearly square to
oblong, and they are filled with dark-brown cell contents.
=Cortex.= The cortex contains parenchyma and stone cells.
The outer layer of the cortical parenchyma cells are variable in size
and many of the cells contain deposits of calcium carbonate and dark
cell contents; the inner parenchyma cells are larger and they are
free of the dark-brown cell contents, but many of the cells contain
deposits of calcium carbonate.
Stone cells with thick, white, porous, and striated walls occur in
among the cortical parenchyma cells.
=Phloem.= The phloem contains sieve cells, phloem, parenchyma, and
bast fibres.
The =sieve cells= are small and with thin, white, angled walls.
The =phloem parenchyma= cells resemble the sieve cells, but they are
larger.
The =bast fibres= occur singly or in groups of two or three. The
walls are white, non-porous, and non-striated.
=Cambium.= The cambium layer is composed of rectangularly shaped
cells, which are frequently obliterated.
=Xylem.= The xylem contains vessels, wood parenchyma, and medullary
rays.
The =vessels= are large, rounded cells with thick walls.
The wood parenchyma consists of thick-walled cells of irregular size
and form.
The =medullary rays= are tangentially elongated and rectangular in
form.
=Pith parenchyma.= The pith parenchyma cells are rounded in outline
and as large as the cortical parenchyma cells.
POWDERED PINK ROOT
When the roots and rhizomes of spigelia are powdered (Plate 93) they
show the following structure:
The epidermal cells are small and brownish on surface view, varying
in size from 13 by 18 micromillimeters to 31 by 40 micromillimeters.
When associated with parenchyma they appear as black masses. The
cortical parenchyma cells are rounded and vary in size from 23 by
26 micromillimeters to 37.5 by 90 micromillimeters. Many of the
cells from the root contain larger quantities of minute single
rounded starch grains varying in size from 1 micromillimeter to 4
micromillimeters. The larger round single starch grains are found in
both the cortical and pith parenchyma of the rhizome. They vary in
size from 5 micromillimeters to 18 micromillimeters. The conducting
elements are pitted tracheids varying from 10 micromillimeters to 38
micromillimeters in diameter. A few pitted and annular vessels are
also found. The only fibres occurring are found in the xylem. They
are not a prominent feature of the powder, as their walls break up
into minute fragments. The pith parenchyma varies in size from 13 by
19 micromillimeters to 75 by 82.5 micromillimeters. It is in these
cells that the largest starch grains occur.
Distinguishing diagnostic characters of the powder:
1. Parenchyma with starch.
2. Dark masses of epidermal tissue.
3. Spigelia should contain starch, and it should not contain
cystoliths, stone cells, or long, white-walled bast fibres.
POWDERED RUELLIA ROOT
When the roots of ruellia root and rhizome are powdered (Plate 94)
they show the following structure:
[Illustration: PLATE 93
POWDERED SPIGELIA MARYLANDICA, L.
1. Epidermis and cortical parenchyma. 2. Tracheids and fibres. 3.
Parenchyma cells of the root containing the small starch grains,
longitudinal view. 4. Parenchyma of the rhizome containing the
large starch grams, transverse view. 5. Tracheids. 6. Surface view
of the epidermal cells. 7. Starch scattered through the field. 8
and 8´. Dark masses of epidermal and underlying tissue.]
[Illustration: PLATE 94
POWDERED RUELLIA CILIOSA, Pursh.
1. Short, broad cystoliths from the rhizome, 1´. Long cystoliths
from the root. 2 and 2´. Long, narrow, white-walled bast fibres. 3.
Tracheal tissue from the xylem of the stem. 4. Root parenchyma. 5.
Tracheal tissue from the xylem of the root. 6. Cortical parenchyma
cells from the rhizome with short, broad cystoliths. 7 and 7´.
Long, thick-walled sclerids from the root. 8. Short, broad sclerids
from the stem. 9. Pitted pith parenchyma from the stem with
intercellular space. 10. Parenchyma of the root with sclerid and
cystolith, longitudinal view.]
The epidermal cells vary from 7.8 by 15.6 micromillimeters to 15.1
by 16.6 micromillimeters. The cell contents are dark and the walls
are light. A few rows of the outer cortical parenchyma cells of both
the rhizome and the root have dark cell contents and white walls. The
dark contents disappear toward the phloem. The cortical cells vary
from 13.6 by 14.3 micromillimeters to 89.5 by 90.9 micromillimeters.
In the cortical parenchyma cells of the rhizome are found the short,
broad cystoliths measuring up to 52 by 62 micromillimeters. In the
corresponding cells of the root are found the long, narrow cystoliths
which measure up to 68.4 by 187.2 micromillimeters. Scattered
throughout the powder are seen three distinct types of sclerids
(stone cells) which are associated with the cortical parenchyma of
both the stem and the root. Most of them are found, however, in
the roots. First, the short, broad stone cells from the stem basis
have square ends; the walls vary from 13 to 19.5 micromillimeters
in thickness with branching pores which extend toward the adjacent
cell. These sclerids vary in size from 52 by 54.6 micromillimeters
to 45 by 130 micromillimeters. Secondly, the long stone cells from
the root vary from 32 by 96 micromillimeters to 45.5 by 542.5
micromillimeters with walls 16 micromillimeters thick. The width of
the cell and the thickness of the wall vary but little throughout
their entire length. The third type of stone cell also from the root
has unequally thickened walls and the ends are square or blunt. A few
long, narrow, colorless, thin-walled bast fibres also occur. They
are 13 micromillimeters wide, with walls 3.9 micromillimeters thick.
Annular spiral and pitted vessels are also found scattered throughout
the powder.
The diagnostic characters of the powder are:
1. The short, broad, and long, narrow cystoliths.
2. The short, broad, and long, narrow sclerids.
3. The long, narrow, thin, white-walled bast fibres.
In poke root, ipecac, sarsaparilla, and veratrum are raphides. In
belladonna and horse-nettle roots are micro-crystals. In calumba,
stillingea, krameria, licorice, scamony root are prisms. In
saponaria, jalap, althea, spikenard, rumex, rhubarb are rosette
crystals. In pleurisy roots both prisms and rosettes occur.
In gentian, senega, symphytuns, lovage, parsley, inula, echinacea,
angelica, burdock, and chicory no crystals of any kind occur. Root
hairs occur in cross-sections of sarsaparilla root and false unicorn,
but with these exceptions: root hairs do not occur on roots, because
the younger part of the root with root hairs is not removed from
the soil when the drug is collected. In sarsaparilla root there
are several layers of hypodermal cells; in most roots there are no
hypodermal cells. In the non-woody roots or the roots of herbs the
parenchyma cells form the greater part of the tissues of the root.
In ruellia root are stone cells; in spigelia root and many other
roots there are no stone cells. In ruellia root are bast fibres; in
spigelia, gentian, ipecac, chicory, dandelion, symphytum, and lovage
no bast fibres occur. In all the woody roots there is a periderm
consisting of typical cork cells, as in black haw; or stone cells, as
in asclepias; or of a mixture of lifeless parenchyma, medullary rays,
etc., as in Oregon grape root.
Woody roots have a phellogen layer which is absent in the non-woody
roots.
The numbers of layers of cortical parenchyma differ in the same
root according to its age, but for a given root there is a normal
variation.
The number of layers of cortical parenchyma in proportion to other
cells is less in woody roots.
In woody roots there is no endodermis. The cambium in these
cases shows clearly between the phloem and the xylem part of the
fibro-vascular bundle.
In woody roots the wood fibres are well developed and form a large
part of the root, and the medullary rays have pitted side and end
walls.
The description given above of ruellia root is not typical of all
roots, but the structure represents the greater number of the
elements that it is possible to find in a root. In many roots, for
instance, there are no stone cells, in others no epidermis and no
endodermis. In asclepias, aconite, and calumba stone cells occur.
In symphytum, chicory, dandelion, burdock, elecampane, pyre thrum,
gentian, and senega no stone cells occur. In aconite, althea,
asclepias, belladonna, bryonia, columba, ipecac, jalap, krameria,
sarsaparilla, scamony, stillingea, and rumex are characteristic
starch grains. Symphytum, chicory, dandelion, burdock, elecampane,
and pyrethrum contain inulin, but no starch. In saponaria, gentian,
and senega neither starch nor inulin occurs.
When studying roots the nature of the epidermis or the periderm must
be considered, as also the number of layers of cortical parenchyma;
the occurrence, distribution, and amount of stone cells when present;
the presence or absence of the endodermis; the occurrence and
structure of bast fibres when present; the nature of the cambium
cells; the width and structure of the medullary rays, the size of the
wood fibres and wood parenchyma, and the nature of the cell contents
and the arrangement of the fibro-vascular bundle.
CHAPTER II
STEMS
When studying stems it should first be determined whether they were
derived from monocotyledonous or dicotyledonous plants. This fact is
ascertained by determining the type of the fibro-vascular bundle. See
Chapter XI. The next fact to determine is whether the stem is from an
herb or from a woody plant. This fact is readily determined because
herbaceous stems have a true epidermis, masses of collenchyma at
the angles of the stem. The cortical cells contain chlorophyll, and
the pith is very large. Woody stems have a corky layer, a phellogen
layer, and the pith is very small except in the very young woody
stems.
Having determined these facts, a study should be made of the
arrangement, form, structure, color, and the cell contents of the
different cells in order to determine the species of plant from which
the stem was obtained.
HERBACEOUS STEMS
The great variation in the structure of herbaceous stems is shown
in the cross-sections of spigelia (Plate 95); in ruellia (Plate
96); in the charts of powdered genuine horehound, powdered spurious
horehound, and in the chart of powdered insect flower stems.
CROSS-SECTION SPIGELIA STEM
Spigelia stem (Plate 95) has the following characteristic structure:
=Epidermis.= The epidermal cells are papillate.
=Cortex.= The cortical parenchyma cells consist of tangentially
elongated cells which are oval in outline.
=Phloem.= The phloem consists of sieve cells, phloem parenchyma, and
of bast fibres.
[Illustration: PLATE 95
CROSS-SECTION OF STEM OF SPIGELIA MARYLANDICA, L.
1. Papillate epidermis. 4. Phloem. 7. Inner phloem.
2. Cortical parenchyma. 5. Cambium. 8. Pith.
3. Bast stereome. 6. Xylem.]
The =sieve cells= are small, and with thin, white, angled walls.
The =phloem parenchyma= resembles the sieve cells, but they are
larger.
The bast fibres are rounded in outline and the walls are thick,
white, non-porous, and non-striated.
=Cambium.= The cambium cells are rectangular in shape or the walls
are collapsed and the cells indistinct.
=Xylem.= The xylem contains vessels, wood parenchyma, medullary rays.
The vessels are small and angled, the walls are thick and white.
=Wood parenchyma.= The cells are variable in size and shape, and
the walls are thick. The medullary ray cells are small, narrow, and
tangentially elongated.
=Internal Phloem.= External to the pith parenchyma are isolated
groups of internal phloem consisting of sieve cells.
=Pith Parenchyma.= The pith parenchyma cells are oval in form and
irregularly placed. The cells contain small, simple starch grains.
RUELLIA STEM
The cross-section of ruellia stem (Plate 96) is as follows:
=Epidermis.= The epidermal cells are variable in shape and very
large. There are no cell contents.
=Cortex.= The cortex consists of collenchyma and parenchyma cells and
stone cells.
The =collenchyma cells= have very small, angled cavities and very
thick walls. These cells make up the greater part of the cortex.
The =cortical parenchyma= cells are variable in size and shape. The
stone cells occur singly or in groups. The walls are thick, white,
porous, and striated, and the central cavity is frequently quite
large.
=Phloem.= The phloem contains sieve cells, phloem parenchyma, and
bast fibres.
The =sieve cells= have thin, white, angled walls.
The =phloem parenchyma= cells are frequently tangentially elongated,
otherwise they resemble the sieve cells.
The =bast fibres= occur alone or in groups. The walls are thick,
white and porous.
[Illustration: PLATE 96
CROSS-SECTION OF STEM OF RUELLIA CILIOSA, Pursh.
1. Epidermis. 2. Collenchyma. 3. Parenchyma. 4. Sclerids. 5. Bast
fibres. 6. Phloem. 7. Cambium cells. 8. Xylem. 10. Pith parenchyma.]
=Cambium.= The cambium cells are rectangular in shape and the walls
are thin.
=Xylem.= The xylem contains vessels, wood parenchyma, and medullary
rays.
The =vessels= are large; the walls are thick, white, and angled.
The =wood parenchyma= cells are variable in size and shape and the
walls are angled.
The =medullary ray cells= are radially elongated and rectangular in
shape.
=Pith Parenchyma.= The pith parenchyma cells are large and rounded in
shape.
POWDERED HOREHOUND
The structure of powdered horehound is shown in Chart 97. The
epidermal cells of the leaf (1) are wavy in outline, the guard cells
are elliptical, the stoma lens-shaped, the epidermis often showing
hairy outgrowth as in the illustration. The epidermal cells of the
petals (2) have irregularly thickened beaded walls. The non-glandular
hairs from the calyx (3); the long, thin-walled, multicellular
non-glandular twisted hairs (4) from the leaves and stems; long,
thin-walled, unicellular hairs (5) from the tube of the corolla; the
glandular hairs (6) with a one-celled stalk and with two secreting
cells divided by vertical walls; the eight-celled glandular hair
(7) as seen in surface and side view; the spiral and reticulated
conducting cells (8); the thick, white-walled fibres from the stem
(9); the pollen grains (10) with nearly smooth walls.
The diagnostic elements of the U. S. P. horehound are the long,
twisted, multicellular hairs (4), the glandular hairs (7), and the
pollen grains (10).
POWDERED SPURIOUS HOREHOUND
Marrubium peregrinum, which is a related species of horehound
and which is a common adulterant of horehound, has the following
structure (Plate 98):
[Illustration: PLATE 97
POWDERED HOREHOUND (_Marrubium vulgare_, L).
1. Epidermis of leaf showing the wavy epidermal cells, stoma,
and a clustered hair. 2. Surface view of the petal epidermis. 3.
Non-glandular hair from the calyx or corolla. 4. Long, thin-walled,
twisted, non-glandular hairs from the leaves and stem. 5.
Unicellular non-glandular hair from the tube of the corolla. 6.
Glandular hairs with a one-celled stalk and with two secreting
cells divided by vertical walls. 7. Surface and side view of the
eight-celled glandular hairs. 8. Conducting cells. 9. Fibres from
the stem. 10. Pollen grains.]
[Illustration: PLATE 98
SPURIOUS HOREHOUND (_Marrubium peregrinum_, L.)
1. Surface view of the leaf epidermis. 2. View of the petal
epidermis. 3. Non-glandular multicellular branched hair from
the stem, leaves, or flowers with a few of the lower branches
broken. 4. Broken pieces and branches from the compound hairs
scattered throughout the field. 5. Unicellular glandular hair
with a two-celled stalk. 6. Under-surface view of an eight-celled
glandular hair. 7. Side view of eight-celled glandular hair. 8.
Long, pointed, unicellular, non-glandular hair from the corolla,
the wall irregularly thickened near the apex. 9. Fibres. 10. Pollen
grains, 11. Conducting cells of leaf.]
[Illustration: PLATE 99
POWDERED INSECT FLOWER STEMS (_Chrysanthemum cinerariifolium_,
[Trev.], Vis.)
1. Surface view of epidermis.
2. Cross-section of epidermis.
3. Hairs.
4. Fibres.
5. Cross-section of fibres.
6. Longitudinal view of pith parenchyma.
7. Cross-section of pith parenchyma.
8. Conducting cells.]
The wavy leaf epidermis (1) with stoma; the beaded wall petal
epidermis (2); the non-glandular, multicellular branched hairs (3)
from the stem leaves or flowers; the broken pieces and branches of
the compound hairs (4) scattered throughout the field; the glandular
hairs (5) with a two-celled stalk; the eight-celled glandular hair
(7) seen in surface view and a side view (8) of a similar hair; the
long, pointed, unicellular non-glandular hair from the tube of the
corolla, the wall irregularly thickened near the apex; the fibres
(9) from the stem; the pollen grains (10) with prominent centrifugal
projections; the conducting cells.
The diagnostic elements of marrubium peregrinum are the multicellular
branched hairs (3) which occur on all parts of the plant, usually
much broken in the powder, with walls many times thicker than the
walls of the hairs found in U. S. P. horehound; the pollen grains
(10) with centrifugal projections and the stalked glandular hairs (5).
INSECT FLOWER STEMS
Insect flower stems are the chief adulterant of insect flowers.
Until the passage of the insecticide law, it was a common practice
to sell (for insect powder) a mixture of powdered stems and flowers.
Since the passage of the law, the presence of the stems in a powder
is supposed to be declared on the label. In spite of the penalties
attached, their presence in a powder is frequently not declared,
as evidenced by a microscopical examination of the insect powders
obtained in the open market.
The structure of powdered insect flower stems (Chart 99) is as
follows:
The epidermal cells of the stems are prominently marked with stoma
and angled, striated wall cells (Fig. 1). On cross-section (Fig.
2) the stem is seen to be made up of epidermal cells with thick
outer and thin side walls (Fig. 2). The T-shaped hairs (Fig. 3) are
longer than those found on any other part of the plant. The fibres
(Fig. 4) are the most characteristic part of the powder. They are
elongated, and the walls are white and slightly porous and of nearly
uniform thickness. They occur free in the field or in groups of two
or more. The cross-section view of these fibres is shown in Fig. 5.
The pith parenchyma (Fig. 6) is abundant and is composed of thick,
porous-walled cells. On cross-section the cells are rounded and are
separated by intercellular spaces. The conducting cells (Fig. 8) vary
from spiral to reticulate.
CHAPTER III
WOODY STEMS
BUCHU STEM
The cross-section of a buchu stem (Plate C), 1.6 millimeters
in diameter, shows a few of the epidermal cells modified into
thick-walled, roughish, unicellular trichomes (1). The remaining
epidermal cells have a thick, wavy outer wall (2). Beneath the
epidermis are several rows of cortical parenchyma cells (3) which
extend to the bast bundles and in which are found the secretory
cavities with the thin-walled secretory cells (4). The bast fibres
(5) occur in continuous bands, varying greatly in size; the walls
are whitish and of variable thickness. Inside the bast fibres, the
small irregular sieve cells (6) occur in groups, surrounded by the
phloem parenchyma (8). The radially elongated cells of the medullary
rays (7) extend outward from the xylem, increasing in number in
the outer portions of the wood, and extending nearly to the bast
fibres. No distinct cambium layer is visible. The conducting cells
(9) occur throughout the xylem surrounded by the wood fibres and
wood parenchyma (10). The latter is not very abundant in buchu. The
medullary rays border on the conducting cells and extend outward to
the phloem. The pith parenchyma cells are nearly circular in outline
and often show a perforated end wall when a cell happens to be cut
just above or below that point.
MATURE BUCHU STEM
In Plate 101-A is shown the cork formation or secondary growth as
seen in the older, larger buchu stems. The wavy epidermis (1),
which is the primary epidermis and which has disappeared on many
portions of the stem, has thin side walls and dark cell contents
(2). Next to the epidermal cells occur several rows of peculiarly
arched cork cells with thick, white outer walls (3) and reddish-brown
cell contents (4). The cork cambium (5) is typical in form, and it
has formed one or two layers of phelloderm cells (6) which have
the same form as the cambium cells but with thicker walls. Next to
the phelloderm occur the cortical parenchyma cells. The remaining
structure of the mature stem is identical with that of Fig. 2.
[Illustration: PLATE 100
CROSS-SECTION OF BUCHU STEMS (_Barosma betulina_ [Berg.],
Barth, and Wendl.)
1. Hairs. 2. Wavy epidermis. 3. Cortical parenchyma. 4. Secretion
cells and cavity. 5. Group of bast fibres. 6. Sieve cells. 7.
Medullary rays. 8. Phloem parenchyma. 9. Vessels. 10. Wood fibres,
and wood parenchyma. 11. Pith parenchyma.]
[Illustration: PLATE 101
_A._ Cross-section of buchu stem (_Barosma betulina_ [Berg.],
Barth. and Wendl.). 1, Outer wall of epidermis; 2, Cell cavity of
epidermal cell; 3, Wall of cork cell; 4, Cavity of cork cell; 5,
Phellogen layer; 6, Divided phellogen cell changing into a cortical
parenchyma cell; 7, Cortical parenchyma cell.
_B._ Cross-section of leptandra rhizome (_Leptandra virginica_
[L.], Nutt.). 1, Parenchyma cells undergoing change in the
composition of their walls; 2, A break in the epidermal tissue; 3,
Parenchyma cells undergoing division.]
POWDERED BUCHU STEM
Powdered buchu stem (Plate 102) has many striking features which
make it easy of identification when mixed with buchu leaves. A
few unicellular, rough, thick, white-walled trichomes (1) occur
distributed throughout the field. They are straight or slightly
curved and vary in length from 40 to 100 microns; in thickness at the
bast they measure from 10 to 22 microns. The central cavity varies
greatly, and in some trichomes seems to have disappeared entirely.
The epidermal cells (2) are very characteristic, occurring singly
or in groups of two or more. The cells from the older stems often
appear reddish brown by transmitted light, while the epidermal cells
from the younger stems appear whitish opaque (porcelain-like).
They are usually six-sided and angular in outline. The cortical
parenchyma cells (3) on transverse view have a rounded cell cavity
and intercellular spaces between the walls. The double walls vary
in thickness, the greatest thickness being about 9 microns. The
parenchyma cells (3) on longitudinal view show square ends and often
contain sphæro-crystalline masses of hesperidin. The thin-walled
sieve cells and the surrounding cells are scarcely ever seen in the
powder. The white-walled pointed stereomes (4) are a characteristic
feature of the powder; they vary greatly in length, in diameter and
in the thickness of their walls. In a number eighty powder the fibres
are mostly broken. The greatest length of the unbroken fibres is
1.25 microns. The thickest wall measured 5 microns and the greatest
observed width was 25 microns. The spiral reticulate and scalariform
thickened conducting cells occur scattered throughout the powder. The
reticulate and scalariform cells usually occur with wood fibres. It
is an interesting fact that the spiral thickening in conducting cells
is usually separate from the side wall and nearly always appears as
indicated at 5. An occasional rosette crystal of calcium oxalate (6)
is seen in the field. The wood parenchyma (7), which makes up a very
small percentage of the xylem, is not readily found in the powder.
The pith parenchyma cells (8) have thick, porous side walls and
perforated side walls. The wood fibres (9) usually occur in masses
surrounding the conducting cells; when occurring singly, the oblique
pores readily distinguish them from the bast fibres.
[Illustration: PLATE 102
POWDERED BUCHU STEMS (_Barosma betulina_ [Berg.],
Barth. and Wendl.).
1. Hairs. 2. Epidermal cells, the larger pieces reddish-brown; the
smaller aggregations white. 3. Transverse cortical parenchyma.
3’ Longitudinal cortical parenchyma with sphæro crystalline
masses of hesperidin. 4. Bast fibres. 5. Spiral, sclariform, and
reticulate vessels. 6. Rosette crystals of calcium oxalate. 7. Wood
parenchyma. 8. Pith parenchyma with porous side and end walls. 9.
Wood fibres.]
The diagnostic elements of powdered buchu stems are:
First, trichomes; secondly, reddish-brown and white-angled epidermal
cells; thirdly, the long, white bast fibres.
CHAPTER IV
BARKS
Barks are all obtained from dicotyledonous plants. In studying
barks there should be ascertained the thickness, arrangement, form,
structure, color, and cell contents of the cells occurring in the
_outer_, _middle_, and _inner_ barks.
The outer bark includes the cork cells and the phellogen layer. The
middle bark includes all the cells occurring between the phellogen
layer and the beginning of the medullary rays. The inner bark
includes the medullary ray cells and all cells associated with them.
The plan of structure of all barks is similar, but in each species of
plant the structure of the bark is uniform and characteristic for the
species.
A great number of drugs consist of the bark of woody plants; for this
reason the bark is considered in a separate chapter from the stem.
WHITE PINE BARK
The cross-section of white pine bark (Plate 103) has the following
structure:
=Outer Bark.= The periderm consists of several layers of
reddish-brown cork cells (1) which are narrow, elongated, and with
thin walls.
=Middle Bark.= The cells forming the middle bark are parenchyma and
secretion cells.
The =parenchyma cells= vary greatly in size, form, and thickness of
the walls. The cells beneath the cork cells and around the secretion
cells are tangentially elongated and oval in shape, while the other
parenchyma cells are more irregular in shape.
The secretion cells are arranged around the schizogenous secretion
cavities. The cells are tangentially elongated, and the walls, which
are slightly papillate, are white.
=Inner Bark.= The cells forming the inner bark are medullary rays,
parenchyma, sieve cells, and storage cavities.
[Illustration: PLATE 103
CROSS-SECTION OF UNROSSED WHITE PINE BARK (_Pinus strobus_, L.)
1. Cork cells of the epidermis. 2. Parenchyma cells filled with
chlorophyl. 3. Intercellular space. 4. Secretion cavity with resin.
5. Secretion cells. 6, One or more circles of parenchyma filled
with chlorophyl. 7. Parenchyma. 8. Medullary rays. 9. Sieve cells.
10. Storage cavities.]
The =medullary rays= form wavy lines. The medullary ray cells are
radially elongated, rectangular in shape, and they contain granular
cell contents. The sieve cells are either square or rectangular in
shape. The walls are thin and white. The storage cavities are either
filled with starch or with prisms and tannin.
POWDERED WHITE PINE BARK
White pine bark (Plate 104) when powdered shows the following
characteristic elements:
The microscopic structure of a powdered white pine is as follows: The
epidermis (1) consists of reddish-brown masses, irregular in outline.
The outer parenchyma cells are of a bright-green color, owing to the
presence of chlorophyll. (The above elements are not usually found in
the rossed bark.) The parenchyma (3) with starch usually occurs in
longitudinal sections accompanied with sieve cells. Often the tissue
separates transversely, showing the medullary rays (4) with their
granular cell contents (9) and the inner parenchyma cells filled with
starch and the surrounding sieve cells.
The crystals are nearly perfect cubes and occur singly (5) or in
groups (6). On the longitudinal section of the bark the crystals
occur in parenchyma cells surrounded by a reddish cell content and
form parallel rows which are very characteristic. The resin occurs
either as white, angled fragments (7) in a water mount, or as
globular mass (8) or as reddish-brown pieces (10). The starch is very
abundant and is distributed through the field. The diagnostic grain
is lens-shaped, with a cleft hilum, which is nearly straight, or
slightly curved, and runs parallel to the long diameter of the grain.
The addition of ferric chlorid T. S. will show the presence of tannin
by forming a dark coloration. The identification of the starch is
facilitated by the addition of a weak Lugol’s solution, which imparts
a blue coloration to the starch grain.
The form, amount, and distribution of the cells composing the bark
differ greatly in different plants.
In cramp bark the cork and phellogen cells are very large, while in
cascara sagrada the phellogen and the cork cells are very small.
[Illustration: PLATE 104
POWDERED WHITE PINE BARK (_Pinus strobus_, L.)
1. Epidermis. 2. Parenchyma cells. 3. Parenchyma with starch. 4.
Medullary rays. 5. Solitary crystals. 6. Solitary crystals and
tannin. 7, 8 and 10. Resin masses. 9. Starch.]
In canella alba bark the periderm is composed of stone cell cork
or stone cells arranged in superimposed rows, which form the outer
layers of the bark.
In white oak and most barks from woody trees the periderm consists of
lifeless parenchyma, medullary rays, sieve cells, bast fibres, and in
some cases stone cells and of phellogen cells.
In young wild cherry, cascara sagrada, and frangula are several
layers of tangentially elongated collenchyma cells with chlorophyll.
In the older barks of the above and in many other barks no
collenchyma cells occur.
In cramp bark and in tulip tree bark the outer layers of the cortical
parenchyma cells are beaded. In most barks there is no beaded walled
parenchyma. The outer layers of most cortical parenchyma cells are
tangentially elongated while the inner parenchyma cells are mostly
circular in outline.
In white oak, cascara sagrada and prickly ash are groups of stone
cells; in the cinnamon barks are bands of stone cells; in cinchona
bark are isolated stone cells. In cramp bark, mezerum, elm, and white
pine bark no stone cells occur.
In frangula, cascara sagrada, cocillina, cinnamon, cinchona,
sassafras, and wild cherry barks the bast fibres occur in groups.
In frangula, cascara sagrada, and cocillina the bast fibres are
surrounded by crystal cells with crystals.
In sassafras bark mucilage cells occur. In canella alba, white pine,
and sassafras barks secretion cells occur; but in most barks no
secretion cells occur.
In sassafras bark the medullary ray cells are nearly as broad as
long; in cramp bark they are elongated and oval in shape. In cascara
sagrada, as in most barks, the cells are longer than broad and
rectangular in shape.
In cascara sagrada the sieve cells are very large; in granatum bark
the sieve cells are very small.
In cassia cinnamon and in canella alba bark the walls of the sieve
cells have collapsed, with the result that the sieve cells have
become partly obliterated.
In witch-hazel, mountain maple, willow, and black walnut are found
prisms; in cramp bark, black haw, wahoo, pomegranate, and cotton root
bark are found rosette crystals; in the cinnamon barks are found
raphides; in cinchona bark, micro-crystals.
In cocillina, frangula, cascara sagrada, white oak, poplar and
Jamaica dogwood barks are found crystal-bearing fibres (Plates 19 and
20).
When studying barks we must consider the kind, structure, and amount
of the periderm; the nature of the phellogen; the nature and amount
of the cortical parenchyma; the occurrence, distribution, and amount
of stone cells, when present; the occurrence and structure of the
bast fibres; the presence or absence of secretion cells; the width,
distribution, and structure of the medullary rays.
CHAPTER V
WOODS
Quite a number of drugs consist of the =wood= of woody plants; such
drugs are quassia, red saunders, white sandalwood, and guaiac.
When studying woods it is necessary to observe the cross, tangential,
and radial sections. Such sections of quassia are shown in Plates
105, 106, and 107. When studying these sections it should be
remembered that while the types of cells forming quassia wood are
similar to the cells forming other woods, still their structure,
arrangement, and amount will vary in a recognizable way in the
different woods.
CROSS-SECTION QUASSIA
Plate 105 is a cross-section of quassia. It has the following
structure:
=Vessels.= The vessels occur singly or in groups of two to eight
cells. The cells are variable in size and shape. The walls are
yellowish white and porous.
=Medullary Rays.= The medullary rays vary from one to five cells in
width.
The =medullary ray cells= are radially elongated and the walls are
strongly porous.
=Wood Parenchyma.= The wood parenchyma cells have thin,
yellowish-white, angled walls.
=Wood Fibres.= The wood fibres have thick, yellowish-white, angled
walls. These cells are smaller in diameter than the wood parenchyma
cells.
RADIAL SECTION QUASSIA
The radial section of quassia (Plate 107) is as follows:
=Vessels.= The vessels appear as in the tangential section.
=Medullary rays.= The medullary rays vary from ten to twenty cells in
height according to the part of the medullary ray bundle cut across.
[Illustration: PLATE 105
CROSS-SECTION OF QUASSIA WOOD (_Picræna excelsa_ [Sw.], Lindl.)
1. Vessels.
2. Medullary rays.
3. Wood parenchyma.
4. Wood fibres.]
[Illustration: PLATE 106
TANGENTIAL SECTION OF QUASSIA WOOD (_Picræna excelsa_ [Sw.], Lindl.)
1. Vessel. 2. Wood parenchyma. 3. Wood fibre. 4. End wall of
medullary ray cell. 5. Medullary ray bundle.]
[Illustration: PLATE 107
RADIAL SECTION OF QUASSIA WOOD (_Picræna excelsa_ [Sw.], Lindl.)
1. Showing the height and length of the medullary rays and cells.
2. Cells with starch.
3. Wood parenchyma and wood fibres.]
The =medullary ray cells= exhibit their height and length. The walls
of the cells are yellowish white and strongly porous.
=Wood Parenchyma.= The wood parenchyma cells have yellowish, thin
walls and blunt end walls.
=Wood Fibres.= The wood fibres have thick, yellowish-white walls, and
the end of the cells are strongly tapering.
TANGENTIAL SECTION QUASSIA
The tangential section of quassia (Plate 106) shows the following
structure:
=Vessels.= The vessels are very long and broad and the yellow walls
are marked with clearly defined pits.
=Medullary Rays.= The tangential section shows the cross-section of
the medullary ray bundle and the cross-section of the medullary ray
cell.
The =medullary ray bundle= varies in width from one to five cells.
The ends of the bundles are always one cell in width, while the
central part of the bundle is frequently five cells in width.
The =medullary ray cell= varies in size, structure, and shape
according to the part of the cell cut across. The cells cut across
the centre show hollow spaces, but the cells cut just above or below
the end wall show a strongly pitted surface. The cells forming the
end of the bundle are larger than the cells forming the centre of the
bundle.
=Wood Parenchyma.= The wood parenchyma cells are greatly elongated
and the walls are thin and yellowish white. The ends of the cells are
blunt.
=Wood Fibres.= The wood fibres are elongated, the walls are thick and
the cells are strongly tapering.
In quassia, white sandalwood, red sandalwood, and guaiac wood are
characteristic crystals.
In quassia the vessels are finely pitted, yellowish, and distinct; in
white sandalwood the vessels are coarsely and sparingly pitted and
white translucent; in red saunders the vessels are coarsely pitted,
bright red and distinct.
When studying woods we must consider the width of the medullary rays,
the structure and cell contents of the medullary ray cells; the
structure, color, and cell contents of the wood parenchyma; also the
wood fibres.
CHAPTER VI
LEAVES
Leaves collectively constitute the greatest manufacturing plant in
the world. Most of the food, clothing, and medicine used by man
is formed as a result of the work of the leaf. The cell contents,
structure, and arrangement of the different cells of the leaf differ
in a marked degree from the cell contents, structure, and arrangement
of the cells in the other organs of the plant. This accounts for the
presence of the large amount of chlorophyll in the leaf, the presence
of stomata, and the peculiar arrangement of the cells.
It should be ascertained if the stomata are above, even with, or
below the epidermis; the nature of the epidermal cells, and, when
present, the nature of the hypodermal cells; the number of layers of
palisade parenchyma and whether it is present on both surfaces of the
leaf, and the nature of the outgrowths from the epidermal cells.
KLIP BUCHU
The cross-section of klip buchu (Plate 108) has the following
structure:
=Epidermis.= The epidermal cells of klip buchu are modified to form
papillæ, the walls are yellowish white, and the papillate portion of
the cell is nearly solid.
=Hypodermis.= The hypodermal cells are never intact because the
mucilage contained in the cells swells when placed in water and
breaks the thin side walls.
=Upper Palisade Parenchyma.= The palisade parenchyma is two layers in
thickness. The cells of the outer layer are greatly elongated and are
packed with chlorophyll. The inner layer of palisade cells is more
irregular, and the cells are much shorter than the cells of the outer
palisade layer.
[Illustration: PLATE 108
CROSS-SECTION OF KLIP BUCHU JUST OVER THE VEIN
_A._ Papillate upper epidermis.
_B._ Hypodermal cells with broken side walls, due to expansion of
mucilage contents.
_C._ Palisade cells, showing two cells filled with chlorophyll.
_D._ Palisade like mesophyll.
_E._ Endodermis.
_F._ Vascular strand of vein.
_G._ Conducting cells with spirally thickened walls.
_H._ Characteristic leaf mesophyll.
_I._ Short, thick palisade cells on the under side of leaf, just
under the vein.
_J._ Under hypodermal cells.
_K._ Papillate under epidermis.]
=Spongy Parenchyma.= The spongy parenchyma cells are branched;
therefore, large intercellular spaces occur between the cells.
=Under Palisade Parenchyma.= The palisade cells of the under
epidermis are short and broad, and they contain fewer chlorophyll
grains than the upper palisade cells of the upper epidermis. These
cells occur only under the veins.
=Under Hypodermis.= The under hypodermal cells are shorter and
broader than the upper hypodermal cells.
=Under Epidermis.= The under epidermal cells are modified to form
papillæ which are similar to the papillæ of the upper epidermis.
=Fibro-Vascular Bundle.= The cells composing the vascular bundle are
sieve cells, vessels, and fibres.
The =sieve cells= are small and the walls are white and angled.
The =vessels= have thick, white, angled walls.
The =bast fibres= are rounded in outline and the walls are thick and
white.
=Endodermis.= The endodermal cells encircle the fibro-vascular
bundles. The cells are large, thin-walled, and oval in shape.
=Secretion Cells.= Near the edges of the leaf are schizogenous
secretion cavities surrounded by thin-walled secretion cells.
POWDERED KLIP BUCHU
When the leaf is powdered (Plate 109), the cells are quite as
characteristic in appearance. The upper epidermal cells (1) have
thick-beaded, yellowish-white walls and papillate outer walls. No
stomata occur on the upper surface. The under epidermis (2) with
numerous stomata, is surrounded by the characteristic guard cells.
The end walls are beaded as on the upper surface. The palisade cells
(3) appear as in the cross-section. The conducting cells (4 and 4)
are of the spiral and pitted type. The papillæ (5 and 5) are very
abundant in the powder and very characteristic. The fragments of the
epidermis (6) are also abundant. The mesophyll (7) is characteristic,
as it retains its form when powdered. The fibres (8) are usually
associated with the conducting cells; occasionally they are found
free as in the illustration.
[Illustration: PLATE 109
POWDERED KLIP BUCHU
1. Upper epidermis. 2. Under epidermis. 3. Palisade cells with
chlorophyll. 4 and 4. Conducting cells. 5 and 5. Papillæ. 6.
Fragments of the epidermis. 7. Mesophyll. 8. Fibres.]
MOUNTAIN LAUREL
=Epidermis.= The epidermal cells of mountain laurel are occasionally
modified, as unicellular hairs (Plate 110, Fig. 1), particularly in
the region of the veins. The ordinary epidermal cells have thick
outer walls and thin inner walls. Beneath many of the epidermal cells
are large air-spaces.
=Upper Palisade Parenchyma.= The palisade parenchyma vary from four
to five layers. The inner palisade cells are shorter and broader than
the outer layer of cells.
=Parenchyma.= The parenchyma cells (Fig. 4) are rounded in form
and they are arranged in the form of columns which are one cell in
thickness above, but two to three cells in thickness near the under
epidermis. Between each chain of cells is a larger intercellular
space (Fig. 6). In a few of the cells are large rosette crystals.
=Under Epidermis.= The under epidermal cells are uniformly smaller
than the upper epidermal cells.
It is thus seen that mountain laurel leaf has no hypodermal cells;
no spongy parenchyma; no under palisade cells; no under hypodermal
cells, and no secretion cavities.
TRAILING ARBUTUS
=Epidermis.= The epidermal cells of the trailing arbutus (Plate 111,
Fig. 2) are variable in size. Many of the cells are modified, as
guard cells (Fig. 1).
=Parenchyma.= The parenchyma cells are round and they are compactly
arranged (Fig. 3) on the upper side of the leaf, but on the under
side they are arranged in round, small, intercellular spaces (Fig.
5). In some of the intercellular spaces are rosette crystals (Fig. 7).
=Under Epidermis.= The under epidermal cells are smaller than the
upper epidermal cells.
It will be seen that the structure of trailing arbutus leaf is very
simple and that its structure is different from that of klip buchu
and mountain laurel.
The structure of powdered leaves is very variable, yet characteristic
for a given species. The leaves from the insect flower plant are
collected with the stems, and ground and sold as a substitute for
insect flowers. These leaves, when powdered, show the following
structure (Plate 112):
[Illustration: PLATE 110
CROSS-SECTION MOUNTAIN LAUREL (_Kalmia latifolia_, L.)
1. Hair. 2. Epidermis. 3. Palisade parenchyma. 4. Parenchyma. 5.
Under epidermis. 6. Intercellular space. 7. Rosette crystal. 8.
Chlorophyll.]
[Illustration: PLATE 111
CROSS-SECTION TRAILING ARBUTUS LEAF (_Epigæa repens_, L.)
1. Stomata. 2. Epidermis. 3. Parenchyma. 4. Cell with chlorophyll.
5. Intercellular space. 6. Under epidermis. 7. Rosette crystal.]
Both the upper and lower epidermis have stomata (Figs. 1 and 2), but
they differ in that the surrounding cells of the upper epidermis
are wavy, while the corresponding cells of the under epidermis are
similar, though the under epidermis has many attached hairs (Figs.
3 and 4). The T-shaped hairs form the most abundant element of the
powder. They are similar in structure to those found on the scales
and stem. Fragments of the mesophyll have round cells and contain
chlorophyll (Fig. 6). The conducting cells are spiral or reticulate.
The different cells of the leaf differ greatly in structure, in
amount, and in arrangement. In uva-ursi, boldus, pilocarpus,
eucalyptus, and chimaphila leaves the outer walls of the epidermal
cell is very thick. In uva-ursi leaves this thick wall appears bluish
green when viewed under low power of the microscope.
In belladonna, stramonium, henbane, peppermint, spearmint, digitalis,
and horehound, the outer wall of the epidermal cells is thin.
In witch-hazel, stramonium, coca, phytolacca, and peppermint there is
a single layer of palisade parenchyma on the upper surface only of
the leaf.
In senna there is one layer of palisade parenchyma on the upper and
one layer on the under side of the leaf. In matico and tea leaves
there are two layers of spongy parenchyma on the upper side of the
leaf.
In chestnut leaves there are three layers of palisade parenchyma on
the upper side of the leaf.
In eucalyptus leaves the entire central part of the leaf, with the
exception of the secretion cells and fibro-vascular bundle, is made
up of the palisade parenchyma.
In some leaves no palisade parenchyma occurs. Trailing arbutus (Plate
111) is an example of such a leaf.
In stramonium leaves the spongy parenchyma is strongly branched; in
mountain laurel the spongy parenchyma is mostly non-branched and
circular in form, as in trailing arbutus (Plate 111, Fig. 3), and as
occurs in the midrib portion of most leaves.
[Illustration: PLATE 112
POWDERED INSECT FLOWER LEAVES
(_Chrysanthemum cinerariifolium_ [Trev.], Vis.)
1. Upper epidermis. 2. Under epidermis showing stoma and hair
scar. 3. Cross-section of under epidermis with attached hair. 4.
Cross-section of upper epidermis. 5. Hairs. 6. Mesophyll with
chlorophyll bodies. 7. Conducting cells.]
In stramonium and chestnut are found rosette crystals. In henbane,
coca, and senna are found prisms. In belladonna, scapola, and
tobacco leaves are found micro-crystals. In most leaves no crystals
occur. In witch-hazel and tea leaves stone cells occur, but in most
leaves there are no stone cells. In eucalyptus, thyme, jaborandi,
buchu, rosemary, and white pine leaves are secretion cells; while
in belladonna, stramonium cells occur. In senna and coca leaves are
crystal-bearing fibres; most leaves do not have crystal-bearing
fibres.
In chimaphila and uva-ursi there are no outgrowths from the epidermal
cells.
In senna, witch-hazel, chestnut, and coca, numerous non-glandular
hairs occur on the epidermis. In tobacco, belladonna, henbane,
pennyroyal, peppermint, and spearmint both glandular and
non-glandular hairs occur on the epidermis.
When studying leaves there should be considered the absence or
presence of outgrowths and their nature; the nature of the epidermis
and, when present, the number of layers of the hypodermis; the nature
of the stoma, whether raised above, even with, or below the level
of the epidermis; the number of layers, and the distribution, when
present, of the palisade parenchyma; the form and amount of the
spongy parenchyma; the absence or presence of secretion cells; the
nature and form of the fibro-vascular bundles, and the nature and
amount of the organic and inorganic cell contents.
CHAPTER VII
FLOWERS
The histological structure of flowers is readily seen in the powder;
therefore, in studying flowers, it is not necessary to section
the various parts. Each part of the flower should be isolated and
powdered separately and each separated part studied. In each case
the powders will contain surface, cross-, and radial sections of the
parts powdered. While studying flowers, special attention should be
given to the pollen grains, to the papillæ of the petals, to the
papillæ of the stigma, and, in certain flowers, to the style tissue.
In the composite flowers special attention should also be given to
the involucre scales, to the scales of receptacle, and, when present,
to the pappus. In addition, attention must be given to secretion
cavities, as in cloves.
POLLEN GRAINS
Pollen grains are one of the most characteristic elements found in
powdered flowers, because they are so small that they are not broken
up when the drug is milled.
The two principal groups of pollen grains are, first, those with
non-spiny walls (Plate 113); and, secondly, those with spiny walls
(Plate 114), as shown in the two charts.
In lavender flowers the pollen grains have six constrictions of the
outer wall. This wall is slightly striated and the cell contents are
granular.
In clover flowers the pollen grains are mostly rounded in outline,
the wall is uniformly thickened, and cell contents are coarsely
granular.
In belladonna flowers the pollen grains terminate in three blunt
points.
In Spanish saffron the pollen grains are spherical and the cell
contents are granular.
[Illustration: PLATE 113
SMOOTH-WALLED POLLEN GRAINS
1. Cloves (_Eugenia caryophyllata_, Thunb.). 2. Santonica
(_Artemisia pauciflora_, Weber). 3. Elder (_Sambucus canadensis_,
L.). 4. Century minor (_Erythræa centaurium_ [L.], Pers.). 5. Pichi
(_Fabiana imbricata_, R. and P.). 6. Cyani. 7. Lavender (_Lavandula
officinalis_, Chaix.). 8. Clover (_Trifolium pratense_, L.). 9.
Belladonna (_Atropa belladonna_, L.). 10. Spanish saffron (_Crocus
sativus_, L.).]
[Illustration: PLATE 114
SPINY WALLED POLLEN GRAINS
1. Anthemis (_Anthemis nobilis_, L.).
2. Arnica (_Arnica montana_, L.).
3. Calendula (_Calendula officinalis_, L.).
4. Cassia flowers.
5. American saffron (_Carthamus tinctorius_, L.).
6. Blue malva flowers (_Malva sylvestris_, L.).]
The non-spiny-walled pollen grains differ not only in microscopic
appearance, but also in size. Clove pollen grains are the smallest,
while Spanish saffron pollen grains are the largest.
NON-SPINY-WALLED POLLEN GRAINS
In cloves the pollen grains show a six-sided, angled cavity and an
outer wall which terminates in three slightly pointed, narrowly
notched portions, separated by nearly straight walls.
In santonica the pollen grains have smooth, unequally thickened
walls, which are strongly constricted at three points, the outline
resembling three half-circles placed together.
In elder flowers the pollen grains appear circular or three-parted.
The wall is of nearly uniform thickness, even at the constricted part
of the grain.
In century minor the pollen grains show three pronounced
restrictions. The wall at these points is very thin. In pichi
flowers the pollen grains are either circular or three-sided and
three-pointed. Inside of each point there is a nearly white pore. In
some of the grains the pollen tube has grown out of one of the pores.
In cyani flowers the pollen grains are longer than broad and the cell
contents appear to be divided into two end portions and an elevated
middle portion.
SPINY-WALLED POLLEN GRAINS
In anthemis the pollen grains have unequally thickened walls
constricted in three places. The spines are short, broad at the base,
and sharp-pointed.
In arnica flowers the pollen grains show three light-colored pores
and numerous short spines.
In calendula flowers the pollen grains show one or more pores,
typically three pores. These pores appear as white spots, and the
wall immediately over the pore is smooth and thinner than the
remaining part of the wall; the spines are very numerous.
In cassia flower pollen grains the outer wall is extended into a
number of rounded projections which are frequently arranged in sets
of fours.
In American saffron flowers the pollen grains show one, two, or three
light-colored pores; the spines are short and broad.
In blue malva flowers the pollen grains are spherical and the outer
wall extends into numerous spinelike projections.
It will be observed that the spiny-walled pollen grains differ
greatly in size, the smallest being the pollen grain of anthemis and
the largest being the pollen grain of blue malva flowers.
In matricaria are numerous, greenish-brown, spiny-walled pollen
grains. In anthemis are multicellular, uniseriate non-glandular hairs
with three or four short, broad, yellow-walled basal cells and a
greatly elongated, thin, gray-walled apical cell.
In arnica are multiseriated branched hairs of the pappus, and
numerous large, yellowish, spiny-walled pollen grains.
STIGMA PAPILLÆ
The =papillæ of the stigma= of most flowers form a characteristic
element even when the flower is powdered. In the case of composite
flowers the papillæ of the disk and ray flowers differ. In American
saffron the papillæ of the style differ in a recognizable way from
the papillæ of the stigma.
The papillæ of the stigma of the ray and disk flowers of arnica,
anthemis, matricaria, and insect flowers differ greatly. Even the
papillæ of the stigma of the ray and disk flowers differ. In all
cases observed the papillæ of the ray flowers are smaller than the
papillæ of the disk flowers.
The papillæ of the stigma of saffron (Plate 115, Fig. 3) are long and
tubular. These papillæ are nearly uniform in diameter, and the apex
is blunt and rounded. The wall is slightly granular in appearance.
The papillæ of the stigma of American saffron (Plate 116, Fig. 2) are
short and tubular. Each papilla is broadest at the base and tapers to
a slender point. The papillæ of that part of the style which emerges
from the corolla (Plate 116, Fig. 1) are large and curved, and the
walls are very thick. The apex of the papilla is frequently solid.
The papillæ of the stigma of the ray flowers of anthemis (Plate 117,
Fig. 1) have thin, slightly striated walls; while the papillæ of the
stigma of the disk flowers (Plate 117, Fig. 2) are longer, the walls
are thicker, and the cell content is denser.
[Illustration: PLATE 115
PAPILLÆ
1. Arnica ray flowers (_Arnica montana_, L.).
2. Insect flower disk (_Chrysanthemum cinerariifolium_ [Trev.], Vis.).
3. True saffron (_Crocus sativus_, L.).]
[Illustration: PLATE 116
PAPILLÆ OF STIGMAS
1. Stigma papillæ of American saffron (_Carthamus tinctorius_, L.)
from that part of the style that emerges from the corolla.
2. Papillæ from the upper part of the stigma of American saffron.
3. Papillæ of the stigma of the disk flowers of arnica (_Arnica
montana_, L.).]
[Illustration: PLATE 117
PAPILLÆ OF STIGMAS
1. Stigma papillæ of the ligulate flowers of anthemis (_Anthemis
nobilis_, L.).
2. Stigma papillæ of the tubular flowers of anthemis.
3. Stigma papillæ of the ligulate flowers of matricaria
(_Matricaria chamomilla_, L.).
4. Stigma papillæ of the disk flowers of matricaria.
5. Stigma papillæ of the ligulate flowers of insect flower
(_Chrysanthemum cinerariifolium_ [Trev.], Vis.).]
The papillæ of the stigma of the ray (Plate 117, Fig. 3) and disk
flowers (Plate 117, Fig. 5) of matricaria are similar in structure,
but the papillæ of the disk flowers are larger.
The papillæ of the stigma of the ligulate flowers of insect flowers
(Plate 117, Fig. 5) are tubular; the walls are striated, and in each
papilla there is a small yellow globule, while the papillæ of the
disk flowers (Plate 115, Fig. 2) are long and tubular, and the walls
are thick.
The papillæ of the stigma of the ray flowers of arnica (Plate 115,
Fig. 1) are very short and tubular. The walls are thin and the cell
contents appear as small, bright-yellow globules, while the papillæ
of the stigma of the disk flowers (Plate 116, Fig. 3) are broadest at
the base, the apex is pointed, and the yellow globules are larger.
The =solitary= hairs are divided into the branched and non-branched
hairs.
POWDERED INSECT FLOWERS
The microscopic examination of insect powder is difficult for the
reason that there are so many elements to be constantly kept in mind.
The parts of the flower which contribute characteristic cells are the
stem, involucre, ray flowers, disk flowers, and the receptacle. In
each of these parts there are many different types of cells.
There are practically two types of flowers found in insect powder of
commerce: first, closed or immature flowers, and secondly, open or
mature flowers. As explained above, the half-open flowers consist
largely of the two above-named varieties. Let us first consider the
structure of the closed insect flowers as illustrated in Plate 118.
[Illustration: PLATE 118
POWDERED CLOSED INSECT FLOWER
(_Chrysanthemum cinerariifolium_, [Trev.] Vis.)
1. Edge of scale. 2. Fibre of scale. 3. Hairs. 4. Upper epidermis
of ray flower. 5. Under epidermis of ray flower. 6. Cross-section
of ray petal. 7. Parenchyma of ray flowers with crystals. 8. Lobe
of disk petal. 9. Filament tissue. 10. Calyx tissue, 11. Lobe of
stamen. 12. Pollen. 13. Papillæ of stigma. 14. Secretion cavity
with surrounding cells. 15. Parenchyma of the receptacle.]
The involucre has many characteristic cells. The more prominent
ones seen in the powder are the edge of the scale with the attached
hair (Fig. 1). These hairs (Fig. 3) are T-shaped. The terminal cell
is expanded laterally, and it terminates in two points. Connecting
the terminal cell with the epidermis are two or three cells which
are slightly longer than broad. In the powder the terminal cell is
usually attached to fragments only of the supporting cells. Fibres of
the bracts have thick, wavy, porous walls, and they have a tendency
to occur in masses. The upper epidermis (Fig. 4) of the ray-flower
petal is prominently papillate. The under epidermis consists of
wavy cells without papillæ. Another view of the papillæ is shown in
Fig. 6. The parenchyma of the ray flowers (Fig. 7) contain cubical
crystals. The lobe of the disk-flower petal (Fig. 8) is papillate at
the end, the terminal cells have thick outer and thin inner walls.
The filament tissue (Fig. 9) is composed of nearly square cells. The
calyx tissue (Fig. 10) is made up of thin-walled cells with slightly
papillate margins. The lobe of the stamen (Fig. 11) consists of
nearly uniform epidermal cells which are in contact throughout their
long diameter, while the hypodermal cells are thin-walled and angled.
The pollen grains (Fig. 12) are dark yellowish green, thin, and the
wall does not appear perforated by pores. The papillæ of the stigma
(Fig. 13) are clustered, club-shaped, and nearly white in color. They
are usually found detached in the powder. All parts of the pistil
contain secreting cells, but the most conspicuous secreting cavities
(Fig. 14) are those of the ovary. These cavities appear brownish in
color and are surrounded by small cells which appear indistinct on
account of the great number of superimposed cells. The parenchyma of
the receptacle occurs in fragments which have strongly marked porous
walls.
OPEN INSECT FLOWERS
Many of the structures of open insect flowers (Plate 119) are
similar to those found in the closed flower. There is practically
no difference in the edge of the scale (Fig. 1); or the fibre of
the scale (Fig. 2); or the T-shaped hairs (Fig. 3); or the upper
epidermis of the ray flower (Fig. 4); or the under epidermis of the
ray flower (Fig. 5); or the cross-section of the ray petal (Fig.
6); or the lobe of the disk petal (Fig. 7); or the filament tissue
(Fig. 8); or the lobe of the stamen (Fig. 9); or the papillæ of
the stigma (Fig. 12); or the parenchyma of the receptacle (Fig.
15). The difference in structure is found, first, in the involucre
scales, which are more fibrous than the scales of the closed flowers;
secondly, in the pollen (Fig. 11), which is less abundant than in the
closed flower; it is also lighter in color and usually shows the wall
perforated by three pores; thirdly, the outer layers of the achene
consist of thick, porous-walled stone cells (Fig. 13), which occur
singly or in groups; fourthly, the secretion cavity is broader and
darker in color (Fig. 14). These differences enable one at once to
distinguish between the closed and open insect flowers. Now, since
the half-closed flowers consist almost wholly of a mixture of equal
parts of closed and open flowers, it follows that the elements of
these two flowers will be mixed in about equal proportions. Thus
we are able to distinguish microscopically the three commercial
varieties of insect powder--namely, closed insect flowers, open
insect flowers, and half-open insect flowers.
[Illustration: PLATE 119
POWDERED OPEN INSECT FLOWER
(_Chrysanthemum cinerariifolium_, [Trev.] Vis.)
1. Edge of involucre scale. 2. Fibres of involucre scale. 3.
Hairs. 4. Upper epidermis of ray flower. 5. Under epidermis of ray
flower. 6. Cross-section of ray petal. 7. Lobe of disk flower. 8.
Filament tissue. 9. Lobe of stamen. 10. Calyx tissue, 11. Pollen.
12. Papillæ of the stigma. 13. Stone cells from the achene and
cross-section of achene. 14. Secretion cavity with surrounding
cells. 15. Parenchyma of the receptacle.]
Insect flowers are the most valuable vegetable insecticide known; yet
much of its effectiveness is destroyed by the adulterants which are
so readily identified by the compound microscope.
POWDERED WHITE DAISIES
A common adulterant found in open insect flowers is the flower-heads
of European daisy (_C. leucanthemum_). Examination of powdered
flowers exported from Europe shows that the entire flower-head is
ground and mixed with the insect flowers. In the cheaper varieties
of open flowers, only the tubular flowers are added after they have
been separated from the heads by crushing and sifting. These tubular
flowers so closely resemble the tubular flowers of the true insect
flowers that it is practically impossible to distinguish between them
macroscopically. The quickest and surest way to identify them is
to reduce a portion of the flowers to a fine powder and examine it
microscopically.
Certain structures of the white daisies (Plate 120) are somewhat
similar to those found in insect flowers. These structures are the
papillæ of the ray petal (Figs. 3, 5, and 13), the lobe of the disk
petal (Fig. 14), and the lobe of the stamen and the pollen (Fig. 8).
The differences are as follows: The under epidermis of the ray
flowers is composed of wavy cells which are more elongated than the
ray flowers of the under epidermis of the ray petal of insect flower.
The filament tissue is made up of slightly beaded cells instead of
smooth-walled cells. The papillæ of the stigma are smaller than the
papillæ of insect flowers. The most striking difference is found
in the structure of the achene. The epidermal tissue of the achene
is composed of palisade cells (Fig. 10), which in the mature form
have thick white walls and scarcely any cavity. These cells swell
perceptibly when placed in water. The other striking feature of the
achene is the bright red resin masses which occur free in the field.
Even a small trace of daisies in insect powder can be identified.
[Illustration: PLATE 120
POWDERED WHITE DAISIES (_Chrysanthemum leucanthemum_, L.)
1 and 2. Scale tissue. 3, 5 and 13. Papillæ of petals. 4. Scale
tissue. 6. Lobe of ray petal. 7. Filament tissue. 8. Pollen. 9.
Papillæ of stigma. 10. Palisade cells of achene. 11. Resin masses.
12. Parenchyma of receptacle. 14. Lobe of dish petal.]
When studying flowers there should be considered the number and
structure of pollen grains; the nature of the papillæ of the stigma
and the petals; the nature of the hairs of the corolla and calyx,
when present. In the composite flowers we should also consider the
structure of the involucre scales, and, when present, the structure
of the receptacle scales, as in the case of anthemus, and of the
pappus hairs, as in the flowers of arnica, boneset, grindelia, and
aromatic goldenrod.
CHAPTER VIII
FRUITS
There is great variation in the structure of fruits, such a
variation, in fact, that no one fruit has a structure typical of all
the other fruits. Each fruit, however, has a pericarp and one or more
seeds. The amount and structure of the cells forming the pericarp
and the seeds of fruits differ in different fruits, but for each
fruit there is a normal amount of, and a characteristic, cellular
structure. Nearly all the important medicinal fruits are cremocarps
or umbelliferous fruits.
The plan of structure of cremocarps is similar, but they all have a
different cellular structure. The epidermis may be simple or modified
as papillæ or hairs. The secretion cavities may be absent (conium),
or, when present, variable in number--cultivated celery seed has six,
wild celery seed up to twelve, and anise up to twenty. The vascular
bundles may be large or small. The endocarp cells may be two or more
layers in thickness. The spermoderm may be thin or thick.
The endosperm cells may vary in size and the cell contents may vary.
CELERY FRUIT
The fruit of celery (Plate 121), like other umbelliferous fruits, is
composed of the pericarp and the seed.
The pericarp is composed of epicarp cells, mesocarp cells, endocarp
cells, and in each rib a vascular bundle. The seed is composed of
the spermoderm, endosperm, and embryo. Each of these parts has a
characteristic structure.
=Epicarp=. The cells of the epicarp (Fig. 1) are papillæ and the
outer wall is striated. The papillæ do not show, however, unless
the cell is cut across the centre, which is the point at which the
papillæ are located.
[Illustration: PLATE 121
CROSS-SECTION OF CELERY FRUIT (_Apium graveolens_, L.)
1. Epicarp. 2. Mesocarp. 3. Vascular bundle. 4. Endocarp. 5.
Spermoderm. 6. Endosperm. 7. Secretion cavity.]
[Illustration: PLATE 122
DIAGRAMMATIC DRAWING OF THE
1. Cross-section of wild celery seed (_Apium graveolens_, L.).
2. Cross-section of cultivated celery seed (_Apium graveolens_, L.).]
=Mesocarp=. In the rib part of the mesocarp (Fig. 2) is a vascular
bundle, and between the ribs one or more secretion cavities. The
vascular bundles are small and are surrounded by irregular-shaped
mesocarp cells.
The =secretion cavities= (Fig. 7) are oval in form and the tissue
bordering the cavity is reddish brown in color. The mesocarp cells
around the secretion cavities are more elongated than the other
mesocarp cells.
=Endocarp=. The endocarp cells are three layers in thickness. These
cells are elongated transversely (Fig. 4).
=Spermoderm=. The cells of the spermoderm are indistinct, compressed,
and dark brown in color (Fig. 5).
=Endosperm=. The endosperm cells (Fig. 6) make up the greater part
of the fruit. The walls which are common to two cells are thick,
non-beaded, and non-pitted, and the cavities of the cells are filled
with aleurone grains.
=Embryo=. The embryo cells, which show only in certain sections, are
similar to endosperm cells.
In anise, hops, sumac, and cumin fruits are characteristic hairs.
In star anise, sabal, allspice, cubeb, pepper, juniper, buckthorn,
and phytolacca fruits are stone cells.
In cubeb, pepper, and cardamon are characteristic masses of aggregate
starch.
In sabal, allspice, and juniper are characteristic secretion cells.
In all the umbelliferous fruits, with the exception of conium, are
yellow to brown secretion cavities.
In cubeb and pepper is aggregate starch. Colocynth contains many
single and double spiral vessels.
Bitter orange contains solitary crystals and spongy parenchyma.
When studying fruits we must consider the nature of the epicarp
cells--whether simple or modified as papillæ or hairs; the form and
structure of the mesocarp cells; the number, size, and structure of
the vascular bundle; the size and number of the secretion cells or
cavities; the number of layers and the structure of the endocarp
cells; the number of layers of stone cells--when present; the color
and width of the spermoderm layer; the structure and cell contents of
the endosperm cells; the nature of the embryo cells, and the nature
of the cell contents.
CHAPTER IX
SEEDS
Seeds are very variable in structure, so much so, in fact, that
scarcely any two seeds have a similar structure. It is necessary,
therefore, when examining seeds, to compare the structure of the seed
under examination with authentic plates or with the section of a
genuine seed. The layers of the seed are the spermoderm, perisperm,
endosperm, and embryo. In some seeds the spermoderm forms the greater
part of the seed; in others the perisperm is greatest in amount;
in still others the cotyledons make up most of the seed, as in the
mustards. The cells forming these different layers differ in form,
structure, and number; therefore it is not difficult to distinguish
and to differentiate between the different seeds when viewed as a
section or as a powder. Almond is studied because it has most of the
layers and cells found in seeds.
SPERMODERM
The =spermoderm= is the thin, brown, granular-appearing skin of the
almond. The layers of the spermoderm are the epidermis, the hypoderm,
the middle layers, and the inner epidermis.
The =epidermis= consists of radially elongated, thick-walled stone
cells which occur alone or in groups of two or more, but seldom as
a continuous layer. The upper or outer part of the stone cells is
non-porous, but the inner walls are strongly porous (Plate 123, Fig.
1).
The =hypoderm=. The cells forming the hypoderm are compressed, the
wall structure is practically indistinguishable, and the whole mass
is reddish brown (Plate 123, Fig. 2).
Occurring in this brown layer are several vascular bundles (Plate
123, Fig. 3).
[Illustration: PLATE 123
CROSS-SECTION SWEET ALMOND SEED
1. Epidermis. 2. Hypoderm. 3. Vascular bundle. 4. Middle layer. 5.
Inner epidermis. 6. Endosperm. 7. Outer layer of the embryo. 8.
Inner layers of the embryo.]
The =middle layers=. The cells forming the middle layers (Fig. 4)
have thin, wavy, light-colored walls which are frequently compressed,
and it is with much difficulty that their outlines are made out.
The =inner epidermis=. The cells forming the inner epidermis are
rectangular in form, and they contain reddish-brown cell contents
(Plate 123, Fig. 5).
ENDOSPERM
The =endosperm=. The cells forming the endosperm are large,
rectangular in outline, usually one layer thick, and they contain
aleurone grains.
EMBRYO
The =embryo=. The cells forming the outer layer of the embryo are
smaller than the inner layers, and they are immediately inward from
the layer of endosperm cells (Plate 123, Fig. 7).
The cells forming the greater part of the embryo are large, rounded,
and they contain aleurone grains and fixed oil (Plate 123, Fig. 8).
In white and black mustard are characteristic mucilage and palisade
cells.
In mix vomica, stropanthus, and St. Ignatius’s bean are
characteristic hairs.
In physostigma and kola are characteristic starch grains.
In henbane, capsicum, stramonium, lobelia, and belladonna seeds are
characteristic epidermal cells.
In areca nut, colchicum, saw palmetto, and nux vomica are
characteristic thick-walled, reserve cellulose cells.
In cardamon seed are aggregate starch masses with irregular outlines.
In bitter and sweet almond, linseed, pepo, and stropanthus are
aleurone grains.
In bitter and sweet almonds are stone cells.
In linseed, quince seed, and in white and black mustard are epidermal
cells with mucilaginous walls and contents, etc.
CHAPTER X
ARRANGEMENT OF VASCULAR BUNDLES
Having familiarized ourselves with the different types of mechanical
and conducting cells, we shall now consider the different ways
in which these cells are associated to form the =vascular= and
=fibro-vascular bundles=.
The simplest form of the vascular bundle occurs in petals, floral
bracts, and leaves. In these parts the vascular bundle is made up of
conducting cells only.
In the great majority of cases, however, the conducting cells are
associated with mechanical cells to form the fibro-vascular bundle.
The fibro-vascular bundle is made up of, first, the =phloem=,
which consists of sieve tubes, companion cells, bast fibres, and
parenchyma; secondly, of the =xylem=, composed of vessels and
tracheids, wood fibres and wood parenchyma; thirdly, of medullary
rays (restricted to certain types); and fourthly, of the bundle
sheath (restricted to certain types).
TYPES OF FIBRO-VASCULAR BUNDLES
There are three well-defined types of the fibro-vascular bundle,
namely, the =radial=, the =concentric=, and the =collateral= types.
RADIAL VASCULAR BUNDLES
The radial type of bundle is met with most frequently in
monocotyledonous roots.
In this form (Plate 114) the xylem forms radial bands of tissue
which alternate with isolated groups of phloem. The space between
the phloem and xylem is filled in with either parenchyma or fibres,
or both. In some cases the vessels of the xylem meet in the centre
of the root, while in other cases the centre of the stem is occupied
by pith parenchyma. Each bundle is surrounded by parenchyma cells,
and in iris, calamus, and veratrum, rhizomes, and endodermis,
surrounds the bundles located in the centre of the stem, consisting
of thin-walled (mechanical) cells.
[Illustration: PLATE 124
CROSS-SECTION OF A RADIAL VASCULAR BUNDLE OF SKUNK CABBAGE ROOT
(_Symplocarpus fœtidus_ [L.], Nutt.)
1. Vessels.
2. Bundle sheath.
3. Parenchyma.
4. Sieve cells.]
[Illustration: PLATE 125
CROSS-SECTION OF A PHLOEM-CENTRIC BUNDLE OF CALAMUS RHIZOME
(_Acorus calamus_, L.)
1. Vessels.
2. Sieve cells.
3. Phloem parenchyma.
4. Parenchyma surrounding the bundles.]
In sarsaparilla root, the pith is composed of thick-walled, porous
pith parenchyma cells with starch. Outside the pith are arranged
radial bands of oval vessels which decrease in size toward the
periphery. Between the ends of these bands occur isolated groups of
sieve cells.
Surrounding the sieve cells and vessels are thick-walled, angled
fibres.
External to these cells is an endodermis composed of lignified
brownish-colored cells one layer in thickness.
CONCENTRIC VASCULAR BUNDLES
There are two principal types of the concentric bundle, namely,
xylem-centric, in which the xylem is centric and the phloem is
peripheral, as in veratrum root; and phloem-centric (Plate 125), in
which the phloem is centric and the xylem peripheral, as in calamus
rhizome.
COLLATERAL VASCULAR BUNDLES
There are three types of collateral vascular bundles--namely, closed
collateral, bi-collateral, and open collateral.
In the closed collateral bundle the phloem and xylem are not
separated by a cambium layer, and in many cases the bundle is
surrounded by thick, angled walled fibres, as in palm stem. The term
closed bundle refers to the fact that there is no cambium between the
xylem and phloem, therefore the bundle is “closed” to further growth,
and not to the fact that it is frequently surrounded by fibres which
prevent further growth. In podophyllum stem (Plate 126) the xylem
portion of the bundle faces the centre of the stem and the phloem
portion of the bundle faces the epidermis. The xylem and phloem are
separated by a cambium layer, and both are surrounded by thick-walled
angled fibres which are the chief mechanical cells of the stem. This
bundle is, in fact, mechanically closed, but not physiologically
because a cambium is present.
[Illustration: PLATE 126
CROSS-SECTION OF A CLOSED COLLATERAL BUNDLE OF MANDRAKE STEM
(_Podophyllum peltatum_, L.)
1. Vessels.
2. Sieve cells.
3. Cambium.
4. Fibres.
5. Parenchyma.
6. Intercellular space.]
[Illustration: PLATE 127
BI-COLLATERAL BUNDLE OF PUMPKIN STEM (_Curcurbita pepo_, L.)
1. Vessels.
2. Sieve tubes.]
BI-COLLATERAL VASCULAR BUNDLES
In the bi-collateral vascular bundle (Plate 127) the xylem is in
between two groups of phloem--namely, an inner group and an outer
group.
In pumpkin stem a bundle occurs in each angle of the stem. The entire
bundle is surrounded by parenchyma cells.
In an individual bundle the xylem consists of large circular vessels
and a phloem containing large sieve cells, many of which show the
yellow porous sieve plates.
OPEN COLLATERAL VASCULAR BUNDLES
In the open collateral bundle (Plate 100) the xylem and phloem are
separated by the cambium layer, which, through its divisions, causes
the stem to increase in thickness each year. This type of bundle is
characteristic of the stems and roots of dicotyledonous plants.
The bi-collateral bundle occurs in many leaves. The xylem in such
cases is central, the phloem strands occupying upper and lower
peripheral positions.
INDEX
Abbé condenser, illustration, 11
Absorption tissue, introduction, 121
tissue of leaves, 125
Aerating tissue, introduction, 151
Annular vessels, illustration of, 129
Bark, of white pine powdered, description of, 250
of white pine powdered, illustration of, 251
unrossed white pine, cross-section, illustration of, 249
Barks, description of, 248
diagnostic structures of, 253
structural variations of, 252
Base sledge microtome, 35
sledge microtome, illustration, 35
Bast fibres, 89
branched, 92
branched, illustrations, 95
crystal bearing, 90, 92
description of, 100
groups of, illustrations, 102
non-porous and non-striated, 96
non-porous and non-striated, illustrations, 101
non-porous and striated, 96
occurrence in powdered drugs, 103
of barks, illustrations, 91, 93, 94
of klip buchu leaf, 262
of ruellia rhizome, 226
of ruellia root, 223
of ruellia stem, 235
of spigelia stem, 235
porous and non-striated, illustrations, 98
porous and striated, 92
porous and striated, illustrations, 97
storage function of, 179
striated and non-porous, illustrations of, 99
Bi-collateral vascular bundles, description of, 298
Buchu stems, cross-section, illustration of, 243
cross-section, illustration of, 244
powdered, description of, 245
powdered, illustration of, 246
Cambium of pink root, 221
of ruellia rhizome, 226
of ruellia stem, 237
of spigelia rhizome, 223
of spigelia stem, 235
Camera lucida, 22
illustrations, 22
Care of microscope, 28
Celery fruit, diagrammatic drawing of, 287
Cell contents, 182
aleurone grains, 197
aleurone grains, description of, 198
aleurone grains, form of, 197
aleurone grains, structure of, 197
aleurone grains, tests for, 198
chlorophyll, 182
crystals, 200
crystals, composition of, 200
crystals, micro-, 200
crystals, raphides, 200
crystals, rosette, 200
crystals, solitary, variation of, 205
cystoliths, 210
cystoliths, forms of, 210
cystoliths, occurrence of, 215
cystoliths, tests for, 215
hesperidin, 196
hesperidin, test for, 196
inulin, 194
inulin, tests for, 194
leucoplastids, 183
mucilage, 194
mucilage associated with raphides, tests for, 194
mucilage, tests for, 194
organic, 182
starch grains, formation of, 183
starch grains, hilum nature of, 188
starch grains, hilum of, 185
starch grains, mounting of, 188
starch grains, occurrence of, 184
starch grains, outline of, 185
starch grains, size of, 185
starch grains, tests for, 188
tannin, 196
tannin, occurrence of, 196
tannin, test for, 197
volatile oil, test for, 196
volatile oils, 196
Cell division common to onion root, 56
Cell plate, 55
Cell sap, 53
Cell, typical, 53
Cell wall, 53
Chromatin, 54
Chromatin granules, 55
Chromatophores, 53
Chromosomes, 55
Closed collateral bundles of mandrake stem, cross-section
illustration of, 296
Collateral vascular bundles, 295
Collenchyma cells, composition of walls, 109
illustrations, 108
occurring in catnip and motherwort, illustrations, 107
of ruellia stem, 235
structure of, 106
Compound microscope, illustration, 10
microscope, mechanical parts of, 7, 8
microscope of Robert Hooke, illustration, 8
microscope, optical parts of, 9, 11, 12
microscopes, introduction, 7
Concentric vascular bundles, 295
Conducting tissue, introduction, 126
Cork cells, origin of, 88
Cortical parenchyma, conduction by, 147
of ruellia stem, 235
Cortex, of pink root, 219
of ruellia rhizome, 226
of ruellia root, 221
of ruellia stem, 235
of spigelia rhizome, 223
of spigelia stem, 233
Cover glasses, 43
illustrations, 44
Crystal cavities, 176
cells, storage function of, 179
Cutting sections, 31
Cystoliths, illustrations of, 214
Cytoplasm, 53
Daisies, white, powdered, description of, 282
illustration of, 283
Dissecting microscope, illustration, 5
needles, 46
needles, illustration, 46
Drawing apparatus, illustration, 23
Ectoplast, 53
Embryo, diagnostic structures of, 291
Endocarp of celery fruit, 288
Endodermal cells, illustrations of longitudinal sections, 119
illustrations of cross-sections, 117
introduction, 116
structure of, 116, 118
Endodermis, of klip buchu leaf, 262
of pink root, 219
of ruellia root, 223
Endosperm of celery fruit, 288
of seeds, 291
Epicarp of celery fruit, 285
Epidermal cells of leaves, storage function of, 179
Epidermis, surface deposits of, 62
of herbaceous stems, illustrations of, 152
of klip buchu leaf, 260
of leaves, illustrations of, 155
of mountain laurel, 264
of pink root, 219
of ruellia rhizome, 226
of ruellia root, 221
of ruellia stem, 235
of seeds, 289
of spigelia rhizome, 223
of spigelia stem, 233
of testa, 63
Epidermis of trailing arbutus, 264
Equatorial plane, 55
plate, 55
Fibro-vascular bundles, composition of, 292
of klip buchu leaf, 262
types of, 292
Flowers, diagnostic structures of, 284
parts of, 270
Folding magnifier, 4
illustration, 4
Fruits, cellular structure of, 285
diagnostic characteristics of, 288
diagnostic structures of, 288
Glandular hairs of peppermint, 178
illustrations of, 165
multicellular, 164
multicellular, multiseriate stalked, 166
multicellular, multiseriate stalked, description of, 166
multicellular, multiseriate stalked, occurrence, 166
multicellular sessile, 164
multicellular stalked, 164
multicellular, uniseriate stalked, 164
stalked, illustrations of, 167
storage function of, 178
unicellular, 164
unicellular, multiseriate stalked, 164
unicellular sessile, 164
unicellular stalked, 164
unicellular, uniseriate stalked, 164
Glandular tissue, introduction, 164
Glass slides, 44
illustrations, 44
Greenough binocular microscope, 15
illustration, 15
Guard cells, 151
Hairs, multicellular, multicellular non-branched, illustration, 75
multicellular, multiseriate branched, of Shepherdia, 78
multicellular, multiseriate branched, 77, 82
multicellular, multiseriate branched, illustrations, 79, 81
multicellular, multiseriate non-branched, 74
multicellular, uniseriate branched, illustration, 76
multicellular, uniseriate non-branched, 72
multicellular, uniseriate non-branched, illustrations of, 73
Hand cylinder microtome, illustration, 34
microtome, 31
microtome, illustration, 31
table microtome, 34
table microtome, illustration, 34
Horehound, powdered, description of, 237
powdered, illustration of, 238
spurious, powdered, description of, 237
spurious, powdered, illustration of, 239
Hypoderm of seeds, 289
Hypodermal cells, of leaves, storage function of, 179
illustrations, 120
structure of, 118
Hypoderms, of klip buchu leaf, 260
of ruellia root, 221
Illumination for microscope, 26
Indirect cell division, 54, 55
Inner bark of white pine, 248
epidermis of seeds, 291
Insect flower leaves, powdered, illustrations of, 268
stems, description of, 241
stems, powdered, illustration of, 240
Insect flowers, closed, powdered, illustration of, 279
open, description of, 280
open, powdered, illustration of, 281
powdered, description of, 278
Intercellular spaces, 158
illustrations of, 160, 161
Internal phloem, of spigelia stem, 235
Inulin, illustrations of, 195
Karyokinesis, 54, 55
Klip buchu, cross-section, illustration of, 261
powdered, description of, 262
powdered, illustration of, 263
Labeling, 47
Latex cavities, 176
tube cavities, 176
tubes, 142, 144
tubes, illustration of, 145
vessels, illustrations of, 146
Leaf epidermis, 59
illustrations, 60, 61
Leaf parenchyma, conduction by, 150
Leaves, diagnostic structures of, 267
stomata, 260
Lenticel, illustration of cross-section, 159
Lenticels, ærating function of, 157
structure of, 158
Linin, 54
Long paraffin process, 29
Machine microtomes, 32
Measuring cylinder, 40
illustration, 40
Mechanical stage, 21
stage, illustration, 22
tissue, 89
Medullary ray, 139
bundle, 139
bundle in tangential-section of quassia wood, 258
cell, 141
cell, arrangement of, in the ray, 142
cell, structure of, 142
cells, in cross-section of quassia wood, 254
cells, in radial-section of quassia wood, 258
cells, in tangential-section of quassia wood, 258
cells, of ruellia stem, 237
Medullary rays, illustration of cross-sections of, 143
illustration of longitudinal section, 140
in cross-section of quassia wood, 254
in radial-section of quassia wood, 254
of pink root, 221
of ruellia rhizome, 227
of ruellia root, 223
of spigelia rhizome, 226
of white pine bark, 250
Mesocarp of celery fruit, 285
Method of mounting specimens, 41
Micro-crystals, illustrations of, 201
lamp, 27
Micrometer eye-pieces, 21
illustrations, 20, 21
Microphotographic apparatus, 24
illustration, 24
Microscope, how to use, 25
Microscopic measurements, 19
Microtome, care of, 36
Middle bark of white pine, 248
lamella, 55
layers of seeds, 291
Minor rotary microtome, 36
illustration, 36
Mountain laurel, cross-section, illustration of, 265
Mucilage cavities, 172, 176
Multicellular hair, 72
Nuclear membrane, 55
spindle, 55
Nucleoli, 55
Nucleus, 53
Objectives, illustrations, 11
Ocular micrometer, 19
illustration, 19
Oil cavities, occurrence, 178
of leaves, 178
of seeds, 178
unicellular, 172
Open collateral vascular bundles, description of, 298
Origin of multicellular plants, 57
Outer bark of white pine, 248
Palisade parenchyma, conduction by, 150
Papillæ, 67
illustrations of, 275
of stigmas, illustrations of, 276, 277
stigma, description of, 274
Paraffin, blocks, 31
embedding oven, illustration, 30
Parenchyma, aquatic plant, 150
cells of white pine, 248
conduction by, 144
cortical, illustrations of, 148
of mountain laurel, 264
of trailing arbutus, 264
pith, illustrations of, 149
Pericycle of pink root, 221
of ruellia root, 223
Periderm, 80
cork, 80
illustrations of, 86
of cascara sagrada, illustrations, 84
of white oak bark, illustration of, 87
parenchyma and stone cells, 85
stone cells, 85
Permanent mounts, 41
Pharmacognostic microscope, illustration, 12
Phloem, centric bundle of calamus, cross-section, illustration of,
294
of ruellia rhizome, 226
of ruellia stem, 235
of spigelia rhizome, 223
of spigelia stem, 233
Phloem parenchyma, conduction by, 150
of pink root, 221
of ruellia rhizome, 226
of ruellia root, 223
of ruellia stem, 235
of spigelia rhizome, 223
of spigelia stem, 235
Photosynthetic tissue, 163
Pink root, description of, 227
Pith parenchyma, conduction by, 147
of pink root, 221
of ruellia rhizome, 227
of ruellia root, 223
of ruellia stem, 237
of spigelia rhizome, 226
of spigelia stem, 235
Pitted vessels, with bordered pores, illustration of, 135
illustrations of, 134
Plant hairs, forms of, 67
introduction, 66
Polar caps, 55
Polarization microscope, 16
illustration, 16
Pollen grains, 270
non-spiny-walled, description of, 273
smooth-walled, illustrations of, 271
spiny-walled, description of, 273
spiny-walled, illustrations of, 272
Preparation of specimens for cutting, 28
Protoplast, 53
Quassia wood, cross-section, illustration of, 255
radial-section, illustration of, 257
Radial vascular bundles, 292
skunk cabbage root, cross-section, illustration of, 293
Raphides, illustrations of, 203
Reading glass, 4
illustration, 4
Reagent set, illustration, 39
Reagents, list of, 38
Research microscope, 13
illustration, 14
Reserve cellulose, illustrations of, 180-181
Reticulate vessels, illustrations of, 133
Root hairs, 121, 122, 125
illustration of, 123
illustration of fragments, 124
Roots and rhizomes, 219
diagnostic structures of, 227
Rosette and solitary crystals, illustrations of, 213
crystals, illustrations of, 204
crystals, inclosed, illustrations of, 206
Ruellia ciliosa, Pursh., powdered, illustration of, 229
ciliosa, Pursh., rhizome, cross-section, illustration of, 225
ciliosa, Pursh., stem, cross-section, illustration of, 236
root, description of, 227
root, illustration of, 222
Scalpels, 46
illustration, 47
Scissors, 46
illustration, 46
Sclariform vessels, illustrations of, 132
Seeds, parts of, 289
Secretion cavities, of celery fruit, 288
description of, 176
illustrations of, 169-171
introduction, 166
lysigenous, 168
schizogenous, 168
schizo-lysigenous, 168
unicellular, 168
Secretion cells, of klip buchu leaf, 262
of white pine, 248
Short paraffin process, 29
Sieve cells, of klip buchu leaf, 262
of pink root, 221
of ruellia rhizome, 226
of ruellia root, 223
of ruellia stem, 235
of spigelia stem, 235
Sieve plate, 138
illustration of, 137
Sieve tube, illustration of, 137
tubes, introduction, 136
tubes, structure, 136
Simple microscope, introduction, 3
Slide box, 48
box, illustration, 48
cabinet, 49
cabinet, illustration of, 49
forceps, 45
forceps, illustrations, 45
tray, 48
tray, illustration, 48
Solitary crystals, illustrations of, 207-209, 211, 212
unicellular hairs, 69
Special research microscope, 14
illustration, 14
Specimens, preservation of, 48
Spermoderm, of celery fruit, 288
of seeds, 289
Spigelia marylandica, powdered, illustration of, 228
rhizome, cross-section, illustration of, 224
root, cross-section, illustration of, 220
stem, cross-section, illustration of, 234
Spindle fibres, 55
Spiral vessels, illustrations of, 129, 130
Spongy parenchyma of klip buchu, 260
Stage micrometer, 19
illustration, 19
Staining dish, 40
illustration, 40
Standardization of ocular micrometer, 19
Starch grains, illustrations of, 186, 187, 189-193
Steinheil lens, 5
illustration, 5
Stems, diagnostic structures of, 233
dicotyledonous, 233
herbaceous, 233
monocotyledonous, 233
Stomata, ærating function of, 151
illustrations of cross-section, 156
relation to surrounding cells, 154
types of, 153
Stone cells, of ruellia root, 223
branched, 109
branched, illustrations of, 110
description, in, 112
introduction, 109
occurrence, illustrations, 115
porous and non-striated, 111
porous and non-striated, illustrations of, 114
porous and striated, 109
porous and striated, illustrations of, 113
storage function of, 178
Storage cavities, 176
cavities, illustrations of, 177
cells, 173
cells, cortical parenchyma, 173
cells, illustrations of, 174
cells, pith parenchyma, 173
cells, wood parenchyma, 173
tissue, 173
walls, description of, 179
Stored mucilage and resin, illustrations of, 175
Surrounding cells, arrangement of, 154
Synthetic tissue, introduction, 163
Temporary mounts, 41
Testa cells, 65
epidermal cells, illustrations, 64
Tracheids of pink root, 221
Trailing arbutus leaf, cross-section, illustration of, 266
Tripod magnifier, 4
illustration, 4
Turntable, 46
illustration, 47
Under epidermis of klip buchu leaf, 262
epidermis of mountain laurel, 264
of trailing arbutus, 264
hypodermis of klip buchu leaf, 262
palisade parenchyma of klip buchu leaf, 262
Unicellular clustered hairs, 72
clustered hairs, illustrations, 71
non-glandular hairs, 69
solitary branched hairs, 72
solitary hairs, illustrations, 70
Upper palisade parenchyma of klip buchu leaf, 260
palisade parenchyma of mountain laurel, 264
Vacuoles, 53
Vascular bundles, arrangement of, 292
occurrence of, 292
Vessels, annular, 127
and tracheids, introduction, 126
in cross-section of quassia wood, 254
in radial-section of quassia wood, 254
in tangential-section of quassia wood, 258
of ruellia rhizome, 226
of ruellia root, 223
of ruellia stem, 237
of spigelia rhizome, 226
pitted, 131
pitted with bordered pores, 131
reticulate, 131
sclariform, 128
spiral, 127
Water pores, aerating function of, 151
Watchmaker’s loupe, 4
illustration, 4
Wood fibres, color of, 104
illustrations, 105
in cross-section of quassia wood, 254
in radial-section of quassia wood, 258
in tangential-section of quassia wood, 258
introduction, 104
structure of, 104
Wood parenchyma, conduction by, 150
in cross-section of quassia wood, 254
in radial-section of quassia wood, 258
of pink root, 221
of ruellia rhizome, 227
of ruellia root, 223
of ruellia stem, 237
of spigelia rhizome, 226
of spigelia stem, 235
Woods, description of, 254
diagnostic structures of, 258
Woody stems, buchu stem, description of, 242
mature buchu stem, 242
Xylem, of pink root, 221
of ruellia rhizome, 226
of ruellia root, 223
of ruellia stem, 237
of spigelia rhizome, 226
of spigelia stem, 235
Transcriber’s Notes
The Table of Illustrations at the beginning of the book was created
by the transcriber.
Inconsistencies in hyphenation such as
“extra-ordinary”/“extraordinary” have been maintained.
Minor punctuation and spelling errors have been silently corrected
and, except for those changes noted below, all misspellings in the
text, especially in dialogue, and inconsistent or archaic usage,
have been retained.
Page 53: “The outer portion of the nucelus” changed to “The outer
portion of the nucleus”.
Page 54: “the centre of the nucelus” changed to “the centre of the
nucleus”.
Page 62: “typical forms of arrangement of epidermal calls” changed
to “typical forms of arrangement of epidermal cells”.
Page 104: “of logwood and santalum rubum” changed to “of logwood
and santalum rubrum”.
Page 107: “the cross-section of catnip stem (_Nepeta cateria_”
changed to “the cross-section of catnip stem (_Nepeta cataria_”.
Page 120: “Cross-section sarsaparilla root (_Smilex officinalis_”
changed to “Cross-section sarsaparilla root (_Smilax officinalis_”.
Page 150: “cells are the narrowest parenchyma cells occuring”
changed to “cells are the narrowest parenchyma cells occurring”.
Page 155: “Upper epidermis of deer tongue (_Trilisia
odoratissima_” changed to “Upper epidermis of deer tongue
(_Trilisa odoratissima_”.
Page 171: “Parenchyma cells with protuding” changed to “Parenchyma
cells with protruding”.
Page 193: “grains of paradise (_Amomum meleguetta_” changed to
“grains of paradise (_Amomum melegueta_”.
Page 237: “Marrubium perigrinum, which is a related species of
horehound” changed to “Marrubium peregrinum, which is a related
species of horehound”.
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