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Title: History of biology
Author: Miall, L. C. (Louis Compton)
Language: English
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1. Typographical errors have been silently corrected.
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* * * * *
[Illustration: KARL ERNST von BAER (in old age), from the
picture by Hagen-Schwarz.
(_By permission of the Berlin Photographic Company, 133 New Bond
Street, London, W._)]
HISTORY OF
BIOLOGY
BY
L. C. MIALL, D.Sc., F.R.S.,
FORMERLY PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF LEEDS
[ISSUED FOR THE RATIONALIST PRESS ASSOCIATION, LIMITED]
London:
WATTS & CO.,
17 JOHNSON'S COURT, FLEET STREET, E.C.
1911
CONTENTS
PAGE
Introduction 1
Biology of the ancients. Extinction of scientific
inquiry. Revival of knowledge.
PERIOD I (1530-1660) 7
Characteristics of the period. The revival of
botany. The revival of zoology. Early notions of
system. The first English naturalists. The rise of
experimental physiology. The natural history of
distant lands (sixteenth century and earlier). Agriculture,
horticulture, and silk-culture in the sixteenth
century.
PERIOD II (1661-1740) 28
Characteristics of the period. The minute anatomists.
Early notions about the nature of fossils. Comparative
anatomy; the study of biological types. Adaptations
of plants and animals; natural theology.
Spontaneous generation. The natural history of
John Ray. The scale of nature. The sexes of
flowering plants.
PERIOD III (1741-1789) 49
Characteristics of the period. Systems of flowering
plants; Linnæus and the Jussieus. Réaumur and
the _History of Insects_. The budding-out of new
animals (Hydra); another form of propagation without
mating (aphids). The historical or comparative
method; Montesquieu and Buffon. Amateur students
of living animals. Intelligence and instinct in the
lower animals. The food of green plants. The
metamorphoses of plants. Early notions about the
lower plants.
PERIOD IV (1790-1858) 89
Characteristics of the period. Sprengel and the
fertilisation of flowers. Cuvier and the rise of
palæontology. Chamisso on the alternation of
generations in Salpa. Baer and the development of
animals. The cell-theory. The scientific investigation
of the higher cryptogams. The enrichment of
English gardens. Humboldt as a traveller and a
biologist. Premonitions of a biological theory of
evolution.
PERIOD V (1859 and Later) 124
Darwin on the _Origin of Species_. Pasteur's experimental
study of microbes.
Chronological Table 141
The Sub-Divisions of Biology 146
Bibliography 147
Index 149
LIST OF ILLUSTRATIONS
PAGE
Karl Ernst von Baer _Frontispiece_
Figure from Fuchs' "Historia Stirpium" 8
Leonhard Fuchs 10
Comparative Figures of Skeletons of Man and
Bird, from Belon's Book of Birds 14, 15
Marcello Malpighi 31
Antony van Leeuwenhoek 33
John Ray 42
Carolus Linnæus 53
Georges Louis Leclerc, Comte de Buffon 65
Georges Cuvier 99
INTRODUCTION
Four hundred years ago, say in the year 1500, Biology, the science
of life, was represented chiefly by a slight and inaccurate natural
history of plants and animals. Botany attracted more students than any
other branch, because it was recognised as a necessary aid to medical
practice. The zoology of the time, extracted from ancient books, was
most valued as a source from which preachers and moralists might draw
impressive emblems. Anatomy and physiology were taught out of Galen to
the more learned of physicians and surgeons. Some meagre notices of the
plants and animals of foreign countries, mingled with many childish
fables, eked out the scanty treatises of European natural history. It
was not yet generally admitted that fossil bones, teeth, and shells
were the remains of extinct animals.
It is the purpose of the following chapters to show how this
insignificant body of information expanded into the biology of the
twentieth century; how it became enriched by a multitude of new facts,
strengthened by new methods and animated by new ideas.
The Biology of the Ancients.
Long before the year 1500 there had been a short-lived science of
biology, and it is necessary to explain how it arose and how it became
quenched. Ancient books and the languages in which they are written
teach us that in very remote times men attended to the uses of
plants and the habits of animals, gave names to familiar species, and
recognised that while human life has much in common with the life of
animals, it has something in common with the life of plants. Abundant
traces of an interest in living things are to be found in the oldest
records of India, Palestine, and Egypt. Still more interesting, at
least to the inhabitants of Western Europe, is the biology of the
ancient Greeks. The Greeks were an open-air people, dwelling in a
singularly varied country nowhere far removed from the mountains or the
sea. Intellectually they were distinguished by curiosity, imagination,
and a strong taste for reasoning. Hence it is not to be wondered at
that natural knowledge should have been widely diffused among them,
nor that some of them should have excelled in science. Besides all the
rest, the Greeks were a literary people, who have left behind them a
copious record of their thoughts and experience. Greek science, and
Greek biology in particular, are therefore of peculiar interest and
value.
Greek naturalists in or before the age of Alexander the Great had
collected and methodised the lore of the farmer, gardener, hunter,
fisherman, herb-gatherer, and physician; the extant writings of
Aristotle and Theophrastus give us some notion of what had been
discovered down to that time.
Aristotle shows a wide knowledge of animals. He dwells upon peculiar
instincts, such as the migration of birds, the nest-building of the
fish Phycis, the capture of prey by the fish Lophius, the protective
discharge of ink by Sepia, and the economy of the hive-bee. He is fond
of combining many particular facts into general statements like these:
No animal which has wings is without legs; animals with paired horns
have cloven feet and a complex, ruminating stomach, and lack the
upper incisor teeth; hollow horns, supported by bony horn-cores, are
not shed, but solid horns are shed every year; birds which are armed
with spurs are never armed with lacerating claws; insects which bear a
sting in the head are always two-winged, but insects which bear their
sting behind are four-winged. He traces analogies between things which
are superficially unlike, such as plants and animals—the mouth of the
animal and the root of the plant. The systematic naturalist is prone to
attend chiefly to the differences between species; Aristotle is equally
interested in their resemblances. The systematic naturalist arranges
his descriptions under species, Aristotle under organs or functions; he
is the first of the comparative anatomists. His conception of biology
(the word but not the thing is modern) embraces both animals and
plants, anatomy, physiology, and system. That he possessed a zoological
system whose primary divisions were nearly as good as those of Linnæus
is clear from the names and distinctions which he employs; but no
formal system is set forth in his extant writings. His treatise on
plants has unfortunately been lost.
Aristotle, like all the Greeks, was unpractised in experiment. It had
not yet been discovered that an experiment may quickly and certainly
decide questions which might be argued at great length without result,
nor that an experiment devised to answer one question may suggest
others possibly more important than the first. Deliberate scientific
experiments are so rare among the Greeks that we can hardly point to
more than two—those on refraction of light, commonly attributed to
Ptolemy, and those by which Pythagoras is supposed to have ascertained
the numerical relations of the musical scale. Aristotle was the last
great man of science who lived and taught in Greece. His writings
disappeared from view for many centuries, and when they were recovered
they were not so much examined and corrected as idolised.
Greece lost her liberty at Chaeronea, and with liberty her fairest
hopes of continued intellectual development. Nevertheless, during
a great part of a thousand years the Greek and Semitic school of
Alexandria cultivated the sciences with diligence and success. We must
say nothing here about the geometry, astronomy, optics, or geography
there taught, but merely note that Herophilus and Erasistratus,
unimpeded by that repugnance to mutilation of the human body which had
been insurmountable at Athens, made notable advances in anatomy and
physiology. From this time a fair knowledge of the bodily structure of
man, decidedly superior to that which Aristotle had possessed, was at
the command of every educated biologist.
The genius of Rome applied itself to purposes remote from science. The
example of Alexandria had its influence, however, upon some inhabitants
of the Roman Empire. Galen of Pergamum in Asia Minor prosecuted the
study of human anatomy. His knowledge of the parts which can be
investigated by simple dissection was extensive, but he was unpractised
in experimental physiology. Hence his teaching, though full with
respect to the skeleton, the chief viscera, and the parts of the brain,
was faulty with respect to the flow of the blood through the heart and
body. Ages after his death the immense reputation of Galen, like that
of Aristotle, was used with great effect to discredit more searching
inquiries. Under the Roman Empire also flourished Dioscorides, who
wrote on the plants used in medicine, and the elder Pliny, who
compiled a vast, but wholly uncritical, encyclopædia of natural history.
We see from these facts how ancient nations, inhabiting the
Mediterranean basin and largely guided by Greek intelligence, had
not only striven to systematise that knowledge of plants and animals
which every energetic and observant race is sure to possess, but
had with still more determination laboured to create a science of
human anatomy which should be serviceable to the art of medicine.
The effort was renewed time after time during five or six centuries,
but was at last crushed under the conquests of a long succession of
foreign powers—Macedonians, Romans, Mohammedan Arabs, and northern
barbarians—each more hostile to knowledge than its predecessors.
Extinction of Scientific Inquiry.
The decline and fall of the Roman Empire brought with it the temporary
extinction of civilisation in a great part of Western Europe. Science
was during some centuries taught, if taught at all, out of little
manuals compiled from ancient authors. Geometry and astronomy were
supplanted by astrology and magic; medicine was rarely practised except
by Jews and the inmates of religious houses. Literature and the fine
arts died out almost everywhere.
No doubt the practical knowledge of the farmer and gardener, as well
as the lore of the country-side, was handed down from father to son
during all the ages of darkness, but the natural knowledge transmitted
by books suffered almost complete decay. The teaching ascribed to
Physiologus is a sufficient proof of this statement. Physiologus
is the name given in many languages during a thousand years to the
reputed author of popular treatises of zoology, which are also called
Bestiaries, or books of beasts. Here it was told how the lion sleeps
with open eyes, how the crocodile weeps when it has eaten a man, how
the elephant has but one joint in its leg and cannot lie down, how the
pelican brings her young back to life by sprinkling them with her own
blood. The emblems of the Bestiaries supplied ornaments to mediæval
sermons; as late as Shakespeare's day poetry drew from them no small
part of her imagery; they were carved on the benches, stalls, porches,
and gargoyles of the churches.
In the last years of the tenth century A.D. faint signs of revival
appeared, which became distinct in another hundred years. From that day
to our own the progress has been continuous.
Revival of Knowledge.
By the thirteenth century the rate of progress had become rapid. To
this age are ascribed the introduction of the mariner's compass,
gunpowder, reading glasses, the Arabic numerals, and decimal
arithmetic. In the fourteenth century trade with the East revived;
Central Asia and even the Far East were visited by Europeans;
universities were multiplied; the revival of learning, painting, and
sculpture was accomplished in Italy. Engraving on wood or copper
and printing from moveable types date from the fifteenth century.
The last decade of this century is often regarded as the close of
the Middle Ages; it really marks, not the beginning, but only an
extraordinary acceleration, of the new progressive movement, which
set in long before. To the years between 1490 and 1550 belong the
great geographical discoveries of the Spaniards in the West and of the
Portuguese in the East, as well as the Reformation and the revival of
science.
PERIOD I.
1530-1660
Characteristics of the Period.
This is the time of the revival of science; the revival of learning
had set in about two centuries earlier. Europe was now repeatedly
devastated by religious wars (the revolt of the Netherlands, the wars
of the League in France, the Thirty Years' war, the civil war in
England). Learning was still mainly classical and scholastic; nearly
every writer whom we shall have occasion to name had been educated at a
university, and was able to read and write Latin. Two great extensions
of knowledge helped to widen the thoughts of men. It became known for
the first time that our planet is an insignificant member of a great
solar system, and that Christendom is both in extent and population but
a small fraction of the habitable globe.
The Revival of Botany.
Botany was among the first of the sciences to revive. Its comparatively
early start was due to close association with the lucrative profession
of medicine. Medicine itself was slow to shake off the unscientific
tradition of the Middle Ages, and its backwardness favoured, as
it happened, the progress of botany. In the sixteenth century the
physician was above all things the prescriber of drugs, and since
nine-tenths of the drugs were got from plants, botanical knowledge was
reckoned as one of his chief qualifications. All physicians professed
to be botanists, and every botanist was thought fit to practise
medicine.
[Illustration:
POLYGONATVM
LATIFOLIVM
FIGURE OF SOLOMON'S SEAL.
From Fuchs' _Historia Stirpium_, 1542. The original occupies a folio
page.]
Three Germans, who were at once botanists and physicians—Brunfels,
Bock, and Fuchs—led the way by publishing herbals, in which the plants
of Germany were described and figured from nature. Their first editions
appeared in the years 1530, 1539, and 1542. Illustrated herbals were
then no novelty, but whereas they had hitherto supplied figures which
had been copied time after time until they had often ceased to be
recognisable, Brunfels set a pattern of better things by producing what
he called "herbarum vivæ eicones," life-like figures of the plants.
Each of the three new herbals contained hundreds of large woodcuts.
Those engraved for Fuchs are probably of higher artistic quality than
any that have appeared since. Each plant, drawn in clear outline
without shading, fills a folio page, upon which the text is not allowed
to encroach. The botanist will, however, remark that enlarged figures
are hardly ever given, so that minute flowers show as mere dots, and
that the details of the foliage are not so scrupulously delineated
as in modern figures. The text of Brunfels and Fuchs is of little
interest, being largely occupied with traditional pharmacy. Bock,
whose figures are inferior to those of Brunfels and Fuchs, makes up
for this deficiency by his graphic and sometimes amusing descriptions.
He delights in natural contrivances, such as the hooks on the twining
stem of the hop, or the elastic membrane which throws out the seeds of
wood-sorrel. Brunfels has no intelligible sequence of species; Fuchs
abandons the attempt to discover a natural succession, and adopts the
alphabetical order; Bock aims at bringing together plants which show
mutual affinity ("Gewächs einander verwandt"), though such natural
groups as he recognises are neither named nor named nor defined.
[Illustration: LEONHARD FUCHS
From his _Historia Stirpium_, 1742.]
These three German herbals really deserve to be called scientific. To
figure the plants of Germany from the life, to exclude such as existed
only in books, and to strive after a natural grouping, was a first
step towards a fruitful knowledge of plant-life. It is worth while to
dwell for a moment upon the place where these herbals were produced.
Along the Rhine civilisation and industry had for many years flourished
together. Here and in the country to the east of the great river had
sprung up that powerful union of seventy cities known in the thirteenth
century as the Confederation of the Rhine; four universities, three of
them on the banks of the Rhine, had been founded; here printing and
wood-engraving had established themselves in their infancy; here, too,
the Reformation found many early supporters. There were historical,
economic, and moral reasons why the first printed books on natural
history, illustrated by woodcuts drawn from the life, should have been
produced in the Rhineland, and why all their authors should have been
Protestants. Nearly every sixteenth-century botanist held the same
faith.
The success of the first German herbalists brought a crowd of
botanists into the field, among whom were several whose names are
still remembered with honour. Gesner of Zurich made elaborate studies
for a great history of plants, which he did not live to complete.
It was he who first pointed out that the flower and fruit give the
best indications of the natural relationships of plants, and his
many beautiful enlarged drawings set an example which has done much
for scientific botany. Botanists began to understand what natural
grouping means, and to recognise that truly natural groups are not
to be invented, but discovered. The almost accidental succession
adopted by Brunfels, the alphabetical succession of Fuchs, the division
according to uses (kitchen-herbs, coronary or garland-flowers, etc.),
and the logical, but too formal, method of Cesalpini, in which, as
in modern classification, much use was made of the divisions in the
ovary—all these were left behind. L'Obel separated, unconsciously
and imperfectly, the Monocotyledons from the Dicotyledons, recognised
several easily distinguished families of flowering plants (grasses,
umbellifers, labiates, etc.), and framed the first synoptic tables of
genera.
The Revival of Zoology.
While the physicians of the Rhineland were describing and figuring
their native plants, the study of animals began to revive. Two
very different methods of work were tried by the zoologists of the
sixteenth century. One set of men, who may be called the Encyclopædic
Naturalists, were convinced that books, and especially the books of
the ancients, constituted the chief source of information concerning
animals and most other things. They extracted whatever they could from
Aristotle, Ælian, and Pliny, adding all that was to be learned from the
narratives of recent travellers, or from the collectors of skins and
shells. The books on which they chiefly depended, being for the most
part written by men who had not grappled with practical natural history
and its problems, were unfortunately altogether inadequate. Many of
the statements brought together by the encyclopædic naturalists were
ill-attested; some were even ridiculously improbable. If inferences
from the facts were attempted—and this was rare—they were more
often propositions of morality or natural theology than the pregnant
thoughts which suggest new inquiries. Hence the encyclopædic plan,
even when pursued by men of knowledge and capacity, such as Gesner and
Aldrovandi, yielded no results proportional to the labour bestowed upon
it; the true path of biological progress had been missed. Naturalists
of another school described and figured the animals of their own
country, or at least animals which they had closely studied. Rondelet
described from personal observation the fishes of the Mediterranean;
Belon described the fishes and birds that he had met with in France and
the Levant. His _Book of Birds_ (1555) is a folio volume in which some
two hundred species are described and figured. The "naturel" (natural
history of the species) contains many curious observations. Perhaps the
best things in the book are two figures placed opposite one another and
lettered in correspondence; one shows the skeleton of a bird, the other
that of a man. The example of Rondelet and Belon was followed by other
zoological monographers, who did more for zoology than all the learning
of the encyclopædists.
Early Notions of System.
Simple-minded people, who do not feel the need of precision in matters
of natural history, have in all ages divided animals into four-footed
beasts which walk on the earth, birds which fly, fishes which swim,
and perhaps reptiles which creep. This is the classification found in
the Babylonian and Hebrew narratives of the great flood. Plants they
naturally divide into trees and herbs. It was not very long, however,
before close observers became discontented with so simple a grouping.
They discovered that the bat is no bird, though it flies; that the
whale is no fish, though it swims; that the snake comes nearer in
all essentials to the four-footed lizard, and even to the beast of
the field, than to the creeping earthworm. At a much later time they
discovered that pod-bearing or rose-like herbs may resemble pod-bearing
or rose-like trees more closely than all trees resemble each other.
Moreover, a multitude of animals became known which cannot be classed
as either beasts, birds, fishes, or reptiles, and a multitude of plants
which cannot be classed as either trees or herbs.
[Illustration: BIRD'S SKELETON.
For comparison with human skeleton (opposite), lettered to show the
answerable bones. From Belon's _Book of Birds_, 1555.]
[Illustration: HUMAN SKELETON.
For comparison with bird's skeleton (opposite), lettered to show the
answerable bones. From Belon's _Book of Birds_, 1555.]
Aristotle found himself obliged to rectify the traditional
classification of animals in order to remove gross anomalies. When
learning decayed the traditional classification came back. Thus the
_Ortus Sanitatis_ (first published in 1475, and often reprinted)
adopts the division into (1) animals and things which creep on the earth;
(2) birds and things which fly; (3) fishes and things which swim. No
consistent primary division of plants was proposed by Greek or Roman,
nor by anyone else until the seventeenth century A.D.
This conflict of systems should have raised questions concerning the
nature of classification and the relative value of characters. Some
of the most striking resemblances found among animals and plants are
only superficial; others, though far less obvious, are fundamental.
Whence this difference? Why should scientific zoology make so little of
the place of abode and the mode of locomotion; so much of the mode of
reproduction and the nature of the skeleton? The answers were vague,
and even the questions were rare and indistinct. But a metaphorical
term came into use which was henceforth more and more definitely
associated with fundamental, as distinguished from adaptive, likeness.
Such likeness was called _affinity_,[1] though no attempt was made
to explain in what sense the term was to be understood. As late as the
year 1835 one of the first botanists in Europe (Elias Fries) could
say no more about affinity between species than that it was _quoddam
supernaturale_, a supernatural property.
A tolerable outline of a classification of animals was attained much
earlier than a tolerable classification of plants. The characters
available for the classification of plants are, to begin with,
less obvious than those which the zoologist can employ. Moreover,
the botanists were restricted to a narrower view of their subject.
Zoologists, though they were expected to bestow the best part of their
time upon vertebrates, were encouraged to study all animals more
or less. Botanists, on the other hand, were practically obliged to
concentrate their attention upon the classification of the flowering
plants. The physician, herb-collector, and gardener cared nothing
about any plants except such as bear flowers and fruit; but of these
they expected full descriptions, and were clamorous for a system which
would enable even a tyro to make out every species with certainty
and ease. The task set before the botanist was comparable in respect
of difficulty with the construction of a detailed and completely
satisfactory classification of birds, which zoology has never yet been
able to produce, while for the sake of this long-unattainable object
almost everything else in botany was neglected.
The First English Naturalists.
During the greater part of three centuries (1300 to 1600), while the
revival of learning and science was proceeding actively in Italy,
France, Switzerland, and the Rhineland, England lagged behind. Humanist
studies were indeed pursued with eminent success in the England of Sir
Thomas More, but there was little else for national pride to dwell
upon. The re-opening of ancient literature, the outpouring of printed
books, the Reformation, the new mathematics and astronomy, the new
botany and zoology, were mainly the work of foreigners. Before the
seventeenth century no Englishman was recognised as the founder of a
scientific school.
Passing over Edward Wotton (1492-1555), who recast the zoology of
Aristotle with very little effect upon the progress of biology, we may
head the list of English naturalists with the name of William Turner
(_d._ 1568), who wrote on the plants and birds of Britain. Turner
was a Reformed preacher, who had been the college friend of Ridley and
Latimer. Being banished for preaching without licence, he studied
medicine and botany in Italy, at Basle and at Cologne. Under Edward
VI. he returned to England and was made Dean of Wells, fled again to
the Continent on Mary's accession, was re-instated by Elizabeth, was
suspended for non-conformity, and died not long after. Turner's herbal
(1551-63) cannot be said to have done much for English botany. The
arrangement is alphabetical, the properties and virtues of the plants
are described out of ancient authors, and most of the figures are
borrowed. Still, it was something to have the common plants of England
examined by a man who had studied under Luke Ghini, had botanised along
the Rhine, and was the pupil, friend, and correspondent of Conrad
Gesner, the most learned naturalist in Europe. Turner's _History_
_of Birds_ (_Historia Avium_) was published in Latin at Cologne
in 1544,[2] and is therefore earlier than Belon's book of birds. The
history contains here and there among passages culled from the ancients
a sprightly description of the feeding or nest-building of some
English bird, and furnishes evidence of the breeding in our islands of
birds which, like the crane, have long been known to us only as rare
visitants. Of the kite Turner says that in the cities of England it
used to snatch the meat out of the hands of children. In his day the
osprey was better known to Englishmen than they liked, for it emptied
their fishponds; anglers used to mix their bait with its fat. Turner
shows not a little of that spirit of close observation which in a later
and more tranquil age shone forth in Gilbert White.
Dr. John Caius (the name is supposed to be a Latinised form of Kay),
the second founder of a great Cambridge college, was physician in
succession to Edward VI., Mary, and Elizabeth; in his youth he had
studied under Vesalius at Padua. Like Turner he was a friend and
correspondent of Gesner, for whom he wrote an account of the dogs of
Britain (_De Canibus Britannicis_, printed in Latin in 1570), which
attempts to classify all the breeds, and to give some account of the
uses to which each was put. The list contains no bull-dog, pointer,
or modern retriever. There is a water-spaniel, however, and dogs had
already been trained to retrieve game. The turnspit, which was not a
distinct breed (Caius calls it a mongrel), has long been superseded.
Curious antiquarian information, such as mention of the weapons
formerly used by sportsmen, and obsolete names of dogs, reward the
reader of this short tract.
Thomas Moufet wrote (for Gesner again) a book on insects, which
incorporated the notes of Penny and Wotton. None of the three lived to
see the printed book, which was at last put forth by Sir Thomas Mayerne
in 1634. It is uncritical, confused, and illustrated by the rudest
possible woodcuts.
John Gerarde's _Herbal_ (1597) and Parkinson's two books of plants
are more amusing than valuable. Both authors were guilty of unscrupulous
plagiarism, a vice which cannot be atoned for by curious figures and
bits of folk-lore, nor even by command of Shakespearean English. Thomas
Johnson's edition of Gerarde (1633) is a far better book than the
original; Ray called it "Gerarde emaculatus"—_i.e._, freed from
its stains.
The succession of influential English naturalists may be said to begin
with Ray, Willughby, and Martin Lister, all of whom belong to the last
half of the seventeenth century.
The Rise of Experimental Physiology.
1543 is a memorable year in the history of science. Then appeared the
treatise of Copernicus on the _Revolutions of the Heavenly Bodies_,
completed long before, but kept back for fear of the cry of novelty
and absurdity which, as he explains in his preface, dull men, ignorant
of mathematics, were sure to raise. The aged astronomer, paralysed and
dying, was able to hold his book in his hands before he passed away.
In the same year Vesalius, a young Belgian anatomist, published his
_Structure of the Human Body_, a volume rich in facts ascertained
by dissection. Some of these facts were held to contradict the teaching
of Galen. Next year Vesalius was driven by the hostility of the medical
profession to burn his manuscripts and relinquish original work; he was
not yet thirty years of age.
Galen had taught that there are two sets of vessels in the body
(arteries and veins), and that in each set there is an ebb and flow.
Knowing nothing of communications between the ultimate branches of
the arteries and veins, and shrinking from the supposition that the
arteries and veins are entirely separate and distinct, Galen had taught
that the blood passes from one set of vessels to the other in the
heart. The septum between the ventricles must be porous and allow the
blood to soak through. Vesalius did not venture openly to challenge the
physiology of Galen, but he significantly admired the "handiwork of
the Almighty," which enables the blood to pass from the right to the
left ventricle through a dense septum in which the eye can perceive no
openings. Fabricius of Acquapendente in 1574 demonstrated the valves of
the veins, though he never arrived at a true notion of their action.
His celebrated pupil, William Harvey, who had been anticipated on
important points by the Spaniard Michael Servetus and Realdo Columbo
of Cremona, published in 1628 a clear account, supported by adequate
experimental evidence, of the double circulation through the body and
the lungs, and of the communications between the arteries and the veins
in the tissues—communications which it was reserved for the next
generation to demonstrate by the microscope.
Aselli of Cremona rediscovered the lacteals in 1622; they had been
known ages before to Erasistratus, but forgotten. Opening the abdomen
of a dog, he saw a multitude of fine white threads scattered over the
mesentery, and observed that when one of them was pricked a liquid
resembling milk gushed out. Further examination showed him that these
vessels, like the veins, possess valves which permit flow in one
direction only. Pecquet, a French physician, announced in 1651 that
the lacteals open into a thoracic duct, which joins the venous system.
In 1653 Rudbeck of Upsala described yet another set of vessels, the
lymphatics; these again are provided with valves, and open into the
thoracic duct, but are filled with a clear liquid.
The effect of these discoveries upon physiology and medicine was
very great, but it did not end there; the whole circle of biological
students and a still wider circle of men who pursued other sciences
were thereby encouraged to follow the experimental path to knowledge.
Wallis, in describing the meetings of scientific men held in London
in 1645 and following years, mentions the circulation of the blood,
the valves in the veins, the lacteals, and the lymphatic vessels among
the subjects which had stirred their curiosity; while the naturalist
Ray thanked God for permitting him to see the vain philosophy which
had pervaded the University in his youth replaced by a new philosophy
based upon experiment—a philosophy which had established the weight
and spring of the air, invented the telescope and the microscope,
and demonstrated the circulation of the blood, the lacteals, and the
thoracic duct.
The Natural History of Distant Lands (Sixteenth Century and Earlier).
Travel and commerce had made the ancient world familiar with many
products of distant countries. Well-established trade routes kept
Europe in communication with Arabia, the Persian Gulf, and India.
Egyptians, Phœnicians, and Greeks explored every known sea, and
brought to Mediterranean ports a variety of foreign wares. Under the
Roman empire strange animals were imported to amuse the populace; silk,
pearls, gay plumage, dyes, and drugs to gratify the luxury of the rich.
Long after the fall of the empire foreign trade was kept up along the
coasts of the Mediterranean. Constantinople was still a great emporium.
Silk was not only imported from the East, but cultivated around
Constantinople in the sixth century. The cotton plant, the sugarcane,
the orange tree, and the lemon tree gradually spread northward and
westward until they became established in Italy, Spain, and the islands
of the Mediterranean.
Western Europe had during many centuries little share in this commerce.
The large and conspicuous animals of Africa and Asia, such as the
elephant, camel, camelopard, ostrich, pelican, parrot, and crocodile,
would have passed out of knowledge altogether but for chance mention
in the Bible and the Bestiaries. Little was done to supplement native
food-plants and drugs by imported products, and the knowledge of
foreign vegetation became as indistinct as that of foreign animals.
In the thirteenth century communication between Western Europe and the
far East was restored. China was thrown open by the Tartar conquest,
and Marco Polo was able to reach the court of Khan Kublai. Pilgrims
from the Holy Land brought back information which, however scanty it
might be, was eagerly received. One of the earliest printed books
(1486) contains the travels of Bernard of Breydenbach, a canon of
Mainz, whose narrative is adorned by curious woodcuts, in which we can
make out a giraffe and a long-tailed macaque.
The geographical discoveries of the sixteenth century gave men for the
first time a fairly complete notion of the planet which they inhabit.
Circumnavigators proved that it is really a globe. Maps of the world,
wonderfully exact considering the novelty of the information which they
embodied, were engraved as early as 1507. The explorers of America
busied themselves not only with the preparation of charts, the conquest
of Mexico and Peru, the search for gold, and the spread of the true
faith, but also with the strange animals and plants which they saw; and
the news which they brought back was eagerly received in Europe. Queen
Isabella charged Columbus, when he set out for his second voyage, to
bring her a collection of bird-skins; but this may be rather a proof
of her love of millinery than of her interest in natural history. Pope
Leo X. liked to read to his sister and the cardinals the Decades of
Peter Martyr Anglerius,[3] in which the productions of the New World
are described. The opossum, sloth, and ant-eater, the humming-bird,
macaw, and toucan, the boa, monitor, and iguana, were made known for
the first time. Potatoes and maize began to be cultivated in the south
of Europe, the tomato was a well-known garden plant, the prickly pear
was spreading along the shores of the Mediterranean, and tobacco was
largely imported. By the end of the seventeenth century Mirabilis and
the garden Tropæolum had been brought from Peru, the so-called African
marigold from Mexico, and sunflowers from North America. More than a
hundred years had still to run before the evening primrose, the passion
flower, and the lobelias of America were to become familiar to European
gardeners, ipecacuanha and cinchona to European physicians.
Agriculture, Horticulture, and Silk-Culture in the Sixteenth Century.
During the darkest parts of the Middle Ages agriculture and
horticulture were regularly practised. Tyranny, the greed of settlers,
the inroads of barbarians, private war, and superstition may destroy
all that brightens human life, but they hardly ever exterminate the
population of large districts,[4] and so long as men live they must
till the soil.
The age of Charlemagne was one of cruel hardship to the inhabitants of
Western Europe, but the cartularies of the great king show that the
improvement of horticulture was a matter of much concern with him. The
nobles and the religious houses kept trim gardens, which are delineated
in mediæval paintings. We know less about the state of the peasantry,
but it is clear that they ploughed, sowed, reaped, and dug their little
gardens, however uncertain the prospect of enjoying the produce of
their labour.
The progressive Middle Ages (about 1000 to 1500 A.D.) greatly
increased the comfort of the wealthy and alleviated the miseries of the
poor. We now hear of countries (England, the Low Countries, the western
half of Germany, the northern half of Italy) where freemen cultivated
their own land, or grew rich by trade, and these men were not content
barely to support life.
Under the later Plantagenets the wool-growers of that upland country
which stretches from Lincolnshire to the Bristol Channel showed
their wealth by building a profusion of manor-houses and beautiful
perpendicular churches, many of which still remain. There can be little
doubt that they were attentive to the rural industries which are so
great a source of comfort and pleasure.
In the sixteenth and seventeenth centuries the Flemings, a laborious
and enterprising people, inhabiting a fertile country, excelled the
rest of Europe in agriculture and horticulture. L'Obel, himself a
Fleming, speaks with pride of the live plants imported into Flanders
from Southern Europe, Asia, Africa, and America. By the close of the
sixteenth century, or a few years later, the lilac, lavender, marigold,
sun-flower, tulip, and crown-imperial, the cucumber and garden rhubarb,
besides many improved varieties of native vegetables, were sent out
from Flanders to all parts of Western Europe. During many generations
English agriculture and horticulture, and not these alone, but English
ship-building, navigation, engineering, and commerce as well, looked
to the Low Countries as the chief schools of invention and the chief
markets from which new products were to be obtained.
Late in the sixteenth century a gentleman of the Vivarais (the modern
Ardèche), named Olivier de Serres, wrote a book on the management of
land,[5] which leaves a strong impression of the zeal for improvement
which then pervaded Europe. De Serres was above all things intent upon
extending silk-culture in France.
On this topic he wrote with full knowledge, having reared silkworms for
thirty-five years. The King, Henri Quatre, shared his hopes, and gave
him practical encouragement. It is well known that a great industry was
thus started; by 1780 the annual yield of silk-cocoons in France was
valued at near a million sterling, while in 1848 it had risen to four
millions. De Serres sought to promote the cultivation of the mulberry
tree, not only because its leaves are the food of the silkworm, but
because he believed that the fibres of the bast would be serviceable
in the manufacture of cordage and cloth. He also tried to revive the
ancient practice of hatching eggs by artificial heat. We learn from him
that the turkey, recently introduced from Mexico, had already become
an important addition to the poultry-yard, while maize from Mexico and
beetroot from the Mediterranean coasts were profitable crops. Among
the new appliances De Serres mentions artificial meadows, wind and
water-mills, cisterns not hewn from stone, and greenhouses.
[1] Aristotle, Cesalpini, Gesner, and Ray are among the writers who use
this word or some synonym.
[2] It has now been made accessible to all readers by the reprint and
translation of Mr. A. H. Evans.
[3] Letter of Peter Martyr, Dec. 26, 1515.
[4] The extermination of the red man in North America is the most
conspicuous case recorded in history. Australia and Tasmania furnish
examples on a smaller scale.
[5] _Le Théâtre d'Agriculture_, 1600.
PERIOD II.
1661-1740
Characteristics of the Period.
In Western Europe this was a time of consolidation succeeding to one
of violent change. Religious wars gave place to dynastic and political
wars. In France the tumults of the preceding hundred years sank to rest
under the rule of a strong monarchy; order and refinement became the
paramount aims of the governing classes; literature, the fine arts, and
the sciences were patronised by the Court. Other nations imitated as
well as they could the example of France. Learning was still largely
classical, but the anti-scholastic revolt, which had first made itself
felt three hundred years earlier, steadily gained ground; Descartes,
Newton, and Locke were now more influential than the Aristotelians.
This was an age of new scientific societies (Royal Society, Academy of
Sciences of Paris, Academia Naturæ Curiosorum, etc.).
The Minute Anatomists.
Magnifying glasses are of considerable antiquity. Seneca mentions the
use of a glass globe filled with water in making small letters larger
and clearer. Roger Bacon (1276) describes crystal lenses which might
be used in reading by old men or those whose sight was impaired. As
soon as Galileo had constructed his first telescopes, he perceived that
a similar instrument might be caused to enlarge minute objects, and
made a microscope which revealed the structure of an insect's eye.
Within twenty years of this date the working opticians of Holland,
Paris, and London sold compound microscopes, which, though cumbrous
as well as optically defective, revealed many natural wonders to the
curious. Simple lenses, sometimes of high power, came before long to
be preferred by working naturalists, and it was with them that all the
best work of the seventeenth and eighteenth centuries was done.
The power of the microscope as an instrument of biological research was
in some measure revealed by Hooke's _Micrographia_ (1665). Robert
Hooke was a man of extraordinary ingenuity and scientific fertility, who
took a leading part in the early work of the Royal Society. He opens
his book with an account of the simple and the compound microscope of
his own day, and then goes on to explain, with the help of large and
elaborate engraved plates, the structure of a number of minute objects.
The most interesting are: A Foraminiferous shell, snow-crystals, a
thin section of cork showing its component cells, moulds, a bit of
Flustra, the under side of a nettle-leaf with its epidermic cells and
stinging-hairs, the structure of a feather, the foot of a fly, the
scales of a moth's wing, the eye of a fly, a gnat-larva, and a flea.
The beauty of the plates and the acuteness of some of the explanations
are remarkable, but lack of connection between the topics discussed
hinders the _Micrographia_ from rising to a very high scientific
level.
Swammerdam treated the microscope as an instrument of continuous
biological research. In his eyes it was a sacred duty to explore with
the utmost faithfulness the minute works of the Creator. Insects
yielded him an inexhaustible supply of natural contrivances, in which
closer scrutiny always brought to view still more exquisite adaptations
to the conditions of life. He was able to throw a beam of steady light
upon the perplexed question of insect-transformation, and swept from
his path the sophistries with which the philosophy of the schools had
obscured the change of the caterpillar into a moth, or of the tadpole
into a frog. He demonstrated the gradual progress of the apparently
sudden transformation of certain insects by dipping into boiling water
a full-fed caterpillar, and then exposing the parts of the moth or
butterfly, which had almost attained their complete form beneath the
larval skin; after this it was easy to discover the same parts in the
pupa.
There is no more valuable chapter in Swammerdam's great work, the
_Biblia Naturæ_, or Book of Nature, than that devoted to the
hive-bee. This insect had long been a favourite study, but only those
who were armed with a microscope and skilled in minute anatomy could
solve the many difficult questions with which it was involved. Aristotle
and other ancient naturalists had spoken of the _king_ of the bees,
which some bee-masters of the seventeenth century had been inclined to
call the queen. Was it really true that the queen was a female, perhaps
the only female in the hive? This question Swammerdam decided by the
clearest anatomical proof—viz., by dissecting out her ovaries. He
pointed out the resemblances between the queen and the workers, such
as the possession of a sting by both, but did not discover the reduced
reproductive organs of the workers, and wrongly declared that they
never lay eggs. He proved by elaborate dissections that the drones are
the males of the community. How and when the queen is fertilised he
could not make out.
[Illustration: MARCELLO MALPIGHI
From an engraving of the oil-painting by A. M. Tobar, presented
to the Royal Society by Malpighi.]
The dissection of the sting, the proboscis, and the compound eye
of the bee was a task after Swammerdam's own heart, but so intricate
that all his patience and skill could not save him from occasional
slips. He bequeathed to his successors many noble examples of the way
in which life-histories ought to be investigated.
Malpighi of Bologna may be called the first of the histologists, for
as early as the second half of the seventeenth century he unravelled
the tissues of many animals and plants. His work on plant-tissues was
so closely accompanied by the similar researches of an Englishman,
Nehemiah Grew, that it is not easy to assign the priority to either.
Malpighi was the first to demonstrate the capillaries which connect the
arteries with the veins, the first to investigate the glands of the
human body and the sensory papillæ of the skin. At the request of our
Royal Society he drew up an account of the structure and life-history
of the silkworm, which is memorable as the earliest anatomical study of
any insect. Malpighi also applied his microscope to the chick-embryo,
and figured its chief stages. His exposition of the formation of the
heart and vessels of the chick is a marvellous example of the quick
appreciation of novel structures.
If we suppose the _Micrographia_ of Hooke to be greatly enlarged,
so as to become, instead of the passing occupation of a man busied with
a hundred other interests, the main pursuit of a long and laborious
life, we shall get a rough notion of the microscopic revelations
of Leeuwenhoek. His researches were desultory, though not quite
so desultory as Hooke's; he must have often spent months upon an
investigation which Hooke would have dismissed in as many weeks.
Both travelled over the whole realm of nature, and lacked that
concentration which made the work of Swammerdam so productive and so
lasting.
[Illustration: ANTONY VAN LEEUWENHOEK.
From the portrait by Verkolje, prefixed to the _Epistolæ ad Soc. Reg.
Angl._, Leyden, 1719.]
Leeuwenhoek worked with simple lenses, ground and mounted by his own
hands. It was easy to make lenses of high magnifying power, but hard to
correct their optical defects, to bring a sufficiently strong light to
bear upon the object, and to focus the lens. When he wished to send out
his preparations for examination by others, he found it best to fix the
objects in the focus, and to provide each with a separate lens. With
such microscopes he managed to study and figure very minute objects,
such as blood-corpuscles, spermatozoa, and bacteria. The spermatozoa
were brought under his notice by a young Dutch physician named Hamm;
but it was Leeuwenhoek's account of them, and his daring theory
of their physiological _rôle_, which gave them such celebrity. To
Leeuwenhoek we owe the first discovery of the rotifers, the infusoria,
Hydra, the yeast-cell, the bacteria, and the generation of aphids
without male parents.
The tradition of the minute anatomists has never been lost, though
we shall be unable to pursue it in these pages. Lyonet (see p. 61)
even surpassed Swammerdam in the elaborate finish of some of his
insect-dissections.
Early Notions about the Nature of Fossils.
Throughout the sixteenth century naturalists held animated debates
about the shells which are found far from the sea, and even on the
top of high hills. Had they ever formed part of living animals or
not? Such a question could hardly have been seriously discussed among
simple-minded people; but the learned men of the sixteenth century were
rarely simple-minded. They had been trained to argue, and argument
could make it plausible that such shapes as these were generated by
fermentation or by the influence of the stars. So prevalent were these
doctrines that it entitles any early philosopher to the respect of
later generations that he should have taken shells, bones, and teeth to
be evidences of animal life. In this singular roll of honour we find
the names of Cesalpini, Palissy, Scilla, Stenson, Hooke, and Woodward.
In England the struggle between philosophy and common-sense was long
kept up. Dr. Ralph Cudworth of Cambridge taught that there is in nature
a subordinate creative force of limited power and wisdom, to whose
imperfections may be attributed the "errors and bungles" which now and
then mar the work. To this subordinate creative force he gave the name
of "vegetative soul," or "plastic nature." None but Cambridge men, it
would appear, felt the weight of Cudworth's reasoning; but several
of these, and especially John Ray[6] and Martin Lister, defended his
conclusions in published treatises. Lister, in a chapter devoted to
"cochlites," or shell-shaped stones, pointed out that they differ from
true shells in being of larger size, in occurring far from the sea, in
being formed of mere stony substance, and in being often imperfect.
Some naturalists had conjectured that the living animals of the
cochlites still exist at great depths in the sea, but Lister evidently
thought otherwise.
In the eighteenth century the belief that fossils are the remains
of actual animals and plants more and more prevailed, the death and
sealing up of the organisms being generally attributed to Noah's
flood. The occurrence of fossils on high mountains seemed so strong
a confirmation of the Biblical narrative that Voltaire was driven
to invent puerile explanations in order to dispel an inference so
unwelcome to him. By the end of the century most naturalists accepted
the doctrine that the great majority of fossils are the remains of
organisms now extinct—a doctrine which was enforced by the remarkable
discoveries of Cuvier (see p. 93). Nearly at the same time William
Smith established the important truth that almost every fossil marks
with considerable precision a particular stage in the earth's history.
Comparative Anatomy: the Study of Biological Types.
Between 1660 and 1740 the scope of natural history became sensibly
enlarged. System had been hitherto predominant, but the systems had
been partial, treating the vertebrate animals and the flowering plants
with as much detail as the state of knowledge allowed, but almost
ignoring the invertebrates and the cryptogams. System was now studied
more eagerly than ever by such naturalists as Ray and Linnæus, but new
aspects of natural history were considered, new methods practised,
new groups of organisms included. Many remarkable vertebrates were
anatomically examined for the first time. Claude Perrault and his
colleagues of the Académie des Sciences dissected animals which had
died in the royal menagerie, and compared the parts and organs of
one animal with those of another; Duverney compared the paw of the
lion with the human hand; in England Tyson studied the anatomy of the
chimpanzee, porpoise, opossum, and rattlesnake, searching everywhere
for the transitions which he believed to connect all organisms, and
to form "Nature's Clew in this wonderful labyrinth of the Creation."
The new microscopes helped to bring the lower and smaller animals into
notice. From 1669, when Malpighi described the anatomy and life-history
of the silkworm, a succession of what we now call biological types were
studied; among these were many invertebrates. Edmund King and John
Master contributed to Willis's treatise _De Anima Brutorum_ (1672)
the anatomies of the oyster, crayfish, and earthworm, all illustrated by
clear and useful plates. Heide (1683) wrote an account of the structure
of the edible mussel (Mytilus), in which mention is made of the ciliary
motion in the gill; Poupart (1706) and Méry (1710) wrote accounts of
the pond-mussel (Anodon). Swammerdam's elaborate studies of insects
and their transformations were followed up by a long succession of
memoirs by Frisch in Germany, Réaumur in France, and (shortly after
the close of the period now under discussion) De Geer in Sweden. The
extraordinary diligence and power of Swammerdam and Réaumur give a
very prominent place in the biology of the seventeenth and eighteenth
centuries to the structure and life-histories of insects. The great
generalisations of comparative anatomy do not belong to this period;
nevertheless, sagacious and luminous remarks are not wanting.
Adaptations of Plants and Animals: Natural Theology.
Natural adaptations and some of the problems which they suggest were
much studied during this period. Bock and Cesalpini had discussed still
earlier the mechanisms of climbing plants, aquatic plants, and plants
which throw their seeds to a distance. Swammerdam figured, not for the
first time, the sporangia and spores of a fern; Hooke the peristome of
a moss. The early volumes of the Académie des Sciences contain many
studies of natural contrivances. Perrault described the retractile claw
of the lion, the pointed papillæ on its tongue, the ruminant stomach
and the spiral valve of a shark's intestine. He improved upon Hooke's
account of the structure of a feather, and his magnified figures of
a bit of an ordinary quill and of a bit of an ostrich-plume might be
inserted into any modern treatise on animal structure.[7] Poupart
followed the later stages of the development of a feather. Méry gave a
minute yet animated description of the wood-pecker's tongue, explaining
how it is rendered effective for the picking up of insects, how it
is protruded and retracted, how it is stowed away when not in use.
Tournefort figured the oblique fibres of a leguminous pod, which he
called _muscles_, and showed how they twist the valves and squeeze
out the seeds.
Natural theology was much in the thoughts of the naturalists who
studied and wrote between 1660 and 1740. Ray discoursed upon the
_Wisdom of God as manifested in the Creation_. Swammerdam regularly
closed the divisions of his _Biblia Naturæ_ with expressions of
pious admiration. A long list of books expressly devoted to the same
theme might be given.[8] One weakness of the natural theologians was
their habit of looking upon the universe as existing for the convenience
of man. Still more fatal was the partiality with which they stated the
facts. While they dwell upon the adaptations which secure the welfare
of particular animals or plants, they are silent about the sufferings
caused by natural processes.
Spontaneous Generation.
During many ages every naturalist thought that he had ample proof of
the generation without parents of animals and plants. He knew that live
worms appear in tightly-closed flasks of vinegar; that grubs may be
found feeding in the cores of apples which show no external marks of
injury; and that weeds spring up in gardens where nothing of the sort
had been seen before. Certain kinds of animals and plants are peculiar
to particular countries; what more likely than that they should be the
offspring of the soil? Fables and impostures supported what all took
to be facts of observation. The great name of Aristotle was used to
confirm the belief that insects were bred from putrefaction; eels and
the fishes called Aphyæ from the mud of rivers. A belief in a process
of transmutation was often combined with a theory of spontaneous
generation. Francis Bacon not only held that insects were born of
putrefying matter, but that oak boughs stuck in the earth produced
vines.
Towards the end of the seventeenth century it occurred to one inquiring
mind that a particular case of spontaneous generation, which had
been accepted by everybody without hesitation, was capable of a less
mysterious explanation. Francesco Redi (1626-1698), physician to the
Duke of Tuscany, published in 1668 an account of his experiments on
the generation of blow-flies. He found that the flesh of the same
animal might yield more than one kind of fly, while the same fly might
be hatched from different kinds of flesh. He saw the flies laying
their eggs in flesh, and dissected eggs out of their ovaries. When he
kept off the flies by gauze the flesh produced no maggots, but eggs
were laid on the gauze. Redi concluded that flies are generated from
eggs laid by the females. He also studied insect-galls, and the worms
which feed on growing seeds. Like earlier observers, he was baffled by
finding live grubs in galls or nuts which were apparently intact, and
by the parasitic worms which are now and then found in the brain-case
and other closed cavities of quadrupeds. Such instances led him to
jump at the supposition of a "vivifying principle," which generated
living things of itself—a supposition contrary to the truer doctrine
which he taught elsewhere. Vallisnieri was able to explain how the egg
is introduced into the rose-gall, which a little later shows no mark
of injury; while Malpighi examined the young nut and found both hole
and egg. How parasitic worms reach the brain-case of the sheep could
be explained only in a later age. Meanwhile Swammerdam, Leeuwenhoek,
Réaumur, and many other special students confirmed and extended Redi's
experiments on the blow-fly; and every fresh instance of normal
generation in a minute organism did something to weaken the belief in
spontaneous generation.
Late in the eighteenth century that belief revived in a form less
easy of refutation. Leeuwenhoek had discovered that organic matter
putrefying in water often yielded abundance of microscopic organisms of
the most diverse kinds, many of which could resist drying in air and
resume their activity when moistened again. Buffon, ever ready with a
speculative explanation, maintained that such minute organisms were
spontaneously generated, and that they were capable of coalescing into
bodies of larger size and more complex structure. Needham supported
Buffon's theories by experiments. Taking infusions of meat, corking
them, and sealing them with mastic, he subjected them to a heat which
he thought intense enough to destroy life; after an interval the
microscope revealed an abundance of living things which he affirmed to
have been generated from dead matter. Spallanzani repeated Needham's
experiments with stricter precautions, sealed his flasks by fusing
their necks in a flame, and then immersing them in boiling water until
they were heated throughout. The infusions in such flasks remained
limpid; no scum formed on the surface; no bad smell was given off
when they were opened; and no signs of life could be detected by the
microscope. To meet the objection that the vegetative force of the
infusions had been destroyed by long heating he simply allowed air
to enter, when the micro-organisms quickly reappeared. Spallanzani's
methods, though far better than any which had been employed before, are
not quite unimpeachable, and could not be relied upon in an atmosphere
rich in germs; but they sufficed to create a strong presumption that
life is set up in infusions by germs introduced with the air.
This was by no means the end of the controversy, which broke out again
and again until it was laid to rest, whether finally or otherwise it
would be unwise to predict, by the experiments of Pasteur.
The Natural History of John Ray.
The sixteenth, seventeenth, and eighteenth centuries each possessed at
least one naturalist of wide learning and untiring diligence, who made
it his care to collect information concerning all branches of natural
history, to improve system, and to train new workers. Gesner, Ray, and
Linnæus occupied in succession this honourable position.
Ray was originally a fellow of Trinity College, Cambridge, who had
risen into notice by proficiency in academical studies. He then became
inspired by the hope of enlarging the knowledge of plants and animals,
and of producing what we should now call a descriptive fauna and flora
of Great Britain. His plan contemplated close personal observation,
travels at home and abroad, and the co-operation of pupils and friends.
[Illustration: JOHN RAY.
From an old engraving of the portrait by Faithorn.]
His chief assistant was Francis Willughby, a young man of wealth and
good family; while Martin Lister, a Cambridge fellow, who had already
laboured at natural history with good effect, undertook an independent
share in the work. Ray wisely began with what lay close at hand, and
published a catalogue of the plants growing around Cambridge. This was
not a mere list of species, but a note-book charged with the results
of much observation and reading. Journeys in quest of fresh material
were begun. Then Ray's well-laid scheme was disconcerted by calamities
which would have overwhelmed a less resolute man. He was driven from
Cambridge by the Act of Uniformity, and forced to serve for years as
a tutor in private families. When this servitude came to an end his
only livelihood was a small pension, bequeathed to him by Willughby,
on which he lived in rustic solitude. Willughby was cut off at the
age of thirty-six, having accumulated much information but completed
nothing. Lister became a fashionable physician, to whom natural history
was little more than an elegant diversion. The whole burden of the
enterprise fell upon Ray, who manfully bore it to the end. He completed
his own share of the work, prepared for the press the imperfect
manuscripts of Willughby, and before he died was able to fulfil the
pledge which he had given forty years before in the prosperity of early
manhood. It is needless to say that the natural history of Britain,
executed in great part by a poor and isolated student, fell far short
of what Ray might at one time have reasonably expected to accomplish.
Ray, like other early naturalists, saw that a methodical catalogue
of species, arranged on some principle which could be accepted in
all times and in all countries, was indispensable to the progress of
natural history, and such a catalogue formed an essential part of his
plan. Perhaps he was a little deficient in that discernment of hidden
affinities which has been the gift of great systematisers, but his
industry, learning, and candour accomplished much. Quadrupeds, birds,
reptiles, fishes, insects, and plants of every sort were reviewed by
him. British species naturally received special attention, but Ray
did not fail to make himself acquainted with the natural productions
of foreign countries, partly by his own travels, and partly by
comparing the descriptions of explorers. He seized every opportunity
of investigating the anatomy and physiology of remarkable animals and
plants, and attended to the practical uses of natural history. British
naturalists owed to him the first serviceable manuals for use in the
field.
Ray was the first botanist who formally divided flowering plants into
Monocotyledons and Dicotyledons. It was only natural that he should now
and then have misplaced plants whose general appearance is deceptive
(lily of the valley, Paris, Ruscus, etc.). He was perhaps the first
to frame a definition of a species; but here his success, as might be
expected, was not great. A species was with him a particular sort of
plant or animal which exactly reproduces its peculiarities generation
after generation. Any plant, for example, which comes up true from
seed, would according to Ray constitute a species. By this definition
many races of plants which are known to have been produced in nurseries
would rank as true species.
The Scale of Nature.
No one can closely examine a large number of plants and animals
without perceiving real or imaginary gradations among them. The
gradation, _shrews_, _monkeys_, _apes_, _man_,
is not very far from a real genealogical succession, confirmed by
structural and historical proofs. The gradation, _fish_,
_whale_, _sheep_, on the other hand, though it seemed equally
plausible to early speculators, is not confirmed by structure and
history. In the age of Aristotle and for long afterwards the ostrich was
believed to be a connecting link between birds and mammals, because it
possessed, in addition to obvious bird-like features, a superficial
resemblance to a camel (long neck, speed in running, desert haunts, and
a rather imaginary resemblance in the toes). Sedentary, branching
zoophytes were quoted as intermediate between animals and plants; corals
and barnacles as intermediate between animals or plants and stones.
Aristotle was convinced of the continuity of nature; his scale of being
extended from inanimate objects to man, and indicated, as he thought, the
effort of nature to attain perfection. Malpighi traced analogies between
plants and animals, identifying the seed and egg, as many had done before
him, assuming that viviparous as well as oviparous animals proceed from
eggs, and comparing the growth of metals and crystals with the growth
of trees and fungi. Leibnitz believed that a chain of creatures, rising
by insensible steps from the lowest to the highest, was a philosophical
necessity. Buffon accepted the same conclusion, and affirmed that every
possible link in the chain actually exists. Pope reasoned in verse
about a "vast chain of being," which reaches from God to man, and from
man to nothing. The eighteenth century was filled with the sound.
Bonnet in 1745 traced the scale of nature in fuller detail than had
been attempted before. He made Hydra a link between plants and
animals, the snails and slugs a link between mollusca and serpents,
flying fishes a link between ordinary fishes and land vertebrates, the
ostrich, bat, and flying fox links between birds and mammals. Man,
endowed with reason, occupies the highest rank; then we descend to the
half-reasoning elephant, to birds, fishes, and insects (supposed to be
guided only by instinct), and so to the shell-fish, which shade through
the zoophytes into plants. The plants again descend into figured stones
(fossils) and crystals. Then come the metals and demi-metals, which are
specialised forms of the elemental earth. Water, air, and fire, with
perhaps the æther of Leibnitz, are placed at the bottom of the scale.
In Bonnet's hands the scale of nature became an absurdity, by being
traced so far and in so much detail. It was not long before a reaction
set in. The great German naturalist, Pallas, in his _Elenchus
Zoophytorum_ (1766) showed that no linear scale can represent the
mutual relations of organised beings; the branching tree, he said,
is the appropriate metaphor. Cuvier taught that the animal kingdom
consists of four great divisions which are not derived one from
another, and his authority overpowered that of Lamarck, who still
maintained that all animals form a single graduated scale. A complete
reversal of opinion ensued, so complete that at length the theologians,
who had once seen in the scale of nature a proof of the wisdom of
Providence, were found fighting with all their might against the
insensible gradations which, according to Darwin's _Origin of Species_,
must have formerly connected what are now perfectly distinct forms of
life.
The eighteenth-century supporters of continuity in nature were not
merely wrong in picturing the organised world as a simple chain or
scale. They were also wrong in assuming that all the links or steps
still exist. We can now see that vast numbers are irrecoverably gone.
It is a safe prophecy that the filiation of species will never be
grasped by the intelligence of man except in outline, and even an
outline which shall truly express the genetic relations of many chief
types is unattainable at present.
The Sexes of Flowering Plants.
As soon as men began to raise plants in gardens, or even earlier, they
must have remarked that plants produce seeds, and that seeds develop
into new plants. The Greeks (Empedocles, Aristotle, Theophrastus)
recognised that the seed of the plant answers to the egg of the animal,
which is substantially though not literally true. None of the three
understood that a process of fertilisation always, or almost always,
precedes the production of seed. Had the date-palm, whose sexes
are separate, and which has been artificially fertilised from time
immemorial, been capable of cultivation in Greece, Aristotle would
not have said that plants have no sexes, and do not require to be
fertilised. His pupil, Theophrastus, knew only by hearsay of the male
and female date-palms, and affirmed that both bear fruit. Pliny, three
hundred years later, called pollen the fertilising substance, and gave
it as the opinion of the most competent observers that all plants are
of two sexes. The revivers of botany paid no attention to pollen or the
function of the flower; it is more surprising that in the following
century Malpighi, who had diligently studied the development of the
plant-embryo, should give so superficial an account of the stamen and
its pollen. About the same time Grew and Millington expressed their
conviction that "the attire" (anthers) "doth serve as the male, for
the generation of the seed."[9] A few years later Ray[10] speaks of
the masculine or prolific seed contained in the stamens. In 1691-4
Camerarius, professor at Tübingen, brought forward clear experimental
proof that female flowers, furnished only with pistils, produce seeds
freely in the neighbourhood of the male or staminate flowers, but
fail to do so when isolated. He distinctly inferred that the anthers
are male organs and the pistil the female organ. The claim set up on
behalf of Linnæus that he demonstrated, or helped to demonstrate,
the sexes of flowering plants has little foundation in fact. To make
out such details of the process of fertilisation as the formation of
pollen-tubes, the penetration of the ovules and the fusion of nuclei
required the improved microscopes of the nineteenth century.
The almost universal presence both in plants and animals of a process
of fertilisation is a fact whose physiological meaning we but
imperfectly grasp. Modern research has shown that the pollen-tube is
exceptional and confined to the flowering plants; the motile filament
of cryptogams, analogous to the spermatozoon of animals, is no doubt
a relatively primitive structure, which gives one of the strongest
indications of the common origin of all forms of life.
[6] Ray came at last to believe that fossils were the remains of actual
organisms, but he was still much hampered by his theological views.
[7] The second of the two has actually been so treated, but without
mention of Perrault's name.
[8] See Krause's _Life of Erasmus Darwin_.
[9] Grew's _Anatomy of Plants_, 1682.
[10] _Wisdom of God_, 1691.
PERIOD III.
1741-1789
Characteristics of the Period.
The chief historical events are the decline of the French monarchy, the
French revolution, the rise of Prussia, the expansion of England, and
the American Declaration of Independence. In the history of thought we
remark the introduction of the historical or comparative method, which
seeks to co-ordinate facts and to trace events to their causes. Science
steadily grows in influence, and freethought wins many triumphs; this
is the age of Voltaire, Rousseau, and the Encyclopædists, of David
Hume, of the French economists and Adam Smith.
Systems of Flowering Plants: Linnæus and the Jussieus.
Linnæus is remembered as a man of great industry, enterprise, and
sagacity, who was inspired from boyhood by a passion for natural
history and spent a long life in advancing it. He was early recognised
as a leader in more than one branch of the study.
L'Obel, Morison, and Ray had laboured to found a natural system of
flowering plants, and it was they who laid the foundation upon which
all their successors have built. The work did not, however, go steadily
forward on the original plan. When Linnæus entered upon the scene the
prevalent systems were only moderately natural, and far from convenient
in practice. To place the undescribed species which poured in from
North America and other distant countries was a difficult task,
with which the universities and botanic gardens of Europe could but
imperfectly cope. Linnæus, who had the instincts of a man of business,
saw that botany was falling into confusion, and that the only remedy
was a quick and easy method, which could be mastered in a few days and
applied with certainty. No such method, he well knew, could take into
account all the intricate affinities of plants, but to devise a perfect
method required the labours of generations of botanists; meanwhile
a temporary expedient, full of faults it might be, would remove a
pressing evil. Flowering plants had been arranged by the divisions
of the ovary, or by the petals and sepals, with no very satisfactory
results; it occurred to Linnæus to try the number of the stamens
and styles. Any such method was bound to present many anomalies,
associating plants which are only distantly related, and separating
plants which are closely related; but some of the worst anomalies were
avoided and some well-established families (Crucifers, Composites,
Labiates) retained at the expense of symmetry. Not even the pressing
need of simple definitions, which was allowed to spoil so natural a
group as the Umbellifers,[11] could induce Linnæus to place Ranunculus
and Potentilla in the same class.
Linnæus gained currency for his system by connecting it with the newly
accepted doctrine of sexes in plants. That doctrine was not conceived
nor demonstrated by him (see p. 48), and it had, as we now see, no
further connection with classification by stamens and styles than that
it explained the almost universal occurrence of such parts in flowering
plants. But Linnæus had persuaded himself that he had done more to
establish the existence of sexes in plants than anybody else, and that
the physiological importance of stamens and styles was a proof of their
systematic value. Neither of these beliefs can stand inquiry, but both
were extremely influential on contemporary opinion. The so-called
Sexual System achieved an immense success everywhere but in France and
Germany. Botanists of small experience were now able to say whether
the plants which seemed to be new were really undescribed or not;
if undescribed, what was their appropriate place in the system. The
congestion of systematic botany was relieved.
The great naturalist appealed to posterity by publishing the sketch of
a natural system of flowering plants, which he accompanied by judicious
expositions of the philosophy of classification. He had the permanent
reform of systematic botany really at heart; he did not believe that
his own Sexual System could be final; and he was glad to help in
setting up a better one. To this end he united groups of genera into
families which he did not pretend to define, being often guided only
by an obscure sense of natural bonds of union. Bernard de Jussieu, one
of the most patient and observant of systematists, devoted his life to
the same task, and profited by the example of Linnæus. He published
nothing, but found expression for his views in the arrangement of a
botanic garden at Versailles. His ideas were afterwards developed by
his nephew, A. L. de Jussieu, in the _Genera Plantarum_ (1789).
Affinity became at length the avowed basis of every botanical system.
No convenience in practice, no agreement or difference in habit, was
knowingly permitted to override this mysterious property. What then is
affinity? What are natural groups of animals and plants, and how do
they arise? Until the year 1859 no one could tell. The terse maxims
of Linnæus helped to guide naturalists into the right road, but a
single fact shows how inadequate they were. Linnæus emphatically and
repeatedly declared his belief in the constancy of species. But if
species were really constant, affinity between species must have been
no more than a delusive metaphor; the resemblances between distinct
species could not, on that supposition, be the effect of inheritance.
Linnæus' imperfect appreciation of the fundamental difference between a
natural classification of living things and such classifications as man
makes for his own practical ends is further revealed by his admission
of a third kingdom of nature.[12] Not only animals and plants, but
rocks and minerals as well, had, he thought, their genera and species.
The genus and species thereby become mere logical terms, independent of
inheritance and of life itself.
Linnæus had a passionate love of order and clearness, enforced by
an inexhaustible power of work. Hence he was able to serve his own
generation with great effect, to methodise the labours of naturalists,
to devise useful expedients for lightening their toil (such as his
strict binomial nomenclature),[13] and to apply scientific knowledge
to the practical purposes of life. But the complexity of nature is not
to be suddenly and forcibly reduced to order, and much of Linnæus'
work had to be done over again in a different spirit. Cuvier furnishes
a somewhat parallel case. Cuvier too was an indomitable worker. His
power of organisation moved the wonder of Napoleon, and there has been
no greater master of clear thought and clear expression. But, like
Linnæus, Cuvier overlooked much that was already obscurely felt and
clumsily worded by brooding philosophers, germs of thought which were
destined to become all-powerful in the course of a generation or two.
It must not be supposed that the labours of Linnæus and Cuvier were
bestowed in vain. All that was really valuable in their writings has
been saved, and biology will never forget how much it owes to their
life-long exertions.
[Illustration: CARL VON LINNÉ (CAROLUS LINNÆUS).
From an engraving (1779) after the portrait by Roslin.]
Réaumur and the History of Insects.
Réaumur was born to wealth, and made timely use of his leisure to study
the sciences and win for himself a place among natural philosophers.
His inclinations directed him first towards mathematics, physics, and,
a little later, towards the practical arts. He took a leading part in a
magnificent description of French industries, which had been undertaken
by the Académie des Sciences. Not content with describing the processes
in use, he perpetually laboured to improve them. The manufacture of
steel, tin-plate, and porcelain, the hanging of carriages and the
fitting of axles, the improvement of the thermometer, glass hives,
and the hatching of fowls' eggs by artificial heat are among the many
objects to which his attention was directed. Natural History gradually
took a more and more prominent place in his studies, and a great
_History of Insects_ engaged the last years of his busy life.
Réaumur was neither an anatomist nor a systematist, at least he
gained no distinction in either of these branches of biology. No
biological laboratory had been dreamt of in his day; he lacked the
manipulative skill of Swammerdam or Lyonet; he was no draughtsman,
and had to engage artists to draw for him. One qualification of
the first importance, however, he possessed in a high degree, the
scientific mind. As he watched the acts of an insect, questions at once
sagacious and practical suggested themselves in abundance, and these
questions he set himself to answer in the best possible way—viz.,
by observation and experiment. In close attention to the activities
of living things his ingenuity and patience found a boundless sphere
of exercise. Moreover all that he had seen he could relate in a
simple but picturesque manner, using the language familiar to the
best French society in the generation next after Madame de Sévigné.
Diffuse but clear, amusing but never frivolous, he won and kept the
attention of a multitude of readers, the best of whom were incited
to adopt his methods or to pursue inquiries which he had indicated.
His greatest successes were won in observing and interpreting the
natural contrivances of insects, the means by which they get their food
and provide for their safety; their transformations, instincts, and
societies. Kirby and Spence, which is still one of the best popular
accounts of insects in English, is largely based upon Réaumur; so
are other well-known treatises, in which the debt is less frankly
acknowledged. Réaumur greatly enlarged the knowledge of all kinds of
insects except the beetles and Orthoptera, which he did not live to
describe, and to this day his _Histoire des Insectes_ is a work of
fundamental importance, with which every investigator of life-histories
is bound to make himself acquainted.
No abstract of Réaumur's _Histoire des Insectes_ is possible, but
we may at least give one example of his mode of treatment. Let us select
his account of the proboscis of a moth, the first full account that
was ever given. He tells us that all moths have not an effective
proboscis, though he does not explain how some of them can dispense
with what seems so necessary an organ; this omission has been made good
by later entomologists. The proboscis, he goes on, springs from the
head, just between the compound eyes. When at rest, it takes up very
little room, for it is spirally rolled, like a watch spring; in some
cases it makes as few as one and a half or two turns, in others as
many as eight or ten; the base is often concealed by a pair of hairy
palps, which serve as feelers. Careful study of a moth as she flits
from flower to flower shows that she alights on the plant, unrolls her
proboscis, passes it into the corolla, withdraws it, perhaps coils it
for an instant, and then plunges it again into the tube. When this
manœuvre has been repeated several times, the moth flies off to another
flower.
Some moths have a tape-like proboscis; in others it is cylindrical. It
can be made to protrude by gentle pressure on the head, or be unrolled
by a pin passed into the centre of the spire; it is composed of
innumerable joints, and tapers from the base to the tip. When forcibly
unrolled, it often splits lengthwise into halves. At the time of escape
from the chrysalis the halves are always free, and they require careful
adjustment in order that a continuous sucking-tube may be obtained.
A newly emerged moth may be seen to roll and unroll its proboscis
repeatedly, until at last the halves cohere in the proper position.
Sometimes they begin to dry before the operation is completed, the
half-tubes get curled, and then the unfortunate moth becomes incapable
of feeding at all. Each half is a demi-canal, whose meeting edges
interlock by minute hooks. The mechanism reminds Réaumur of that which
connects the barbs of a feather; in both cases the hooks can be
adjusted rapidly and completely by stroking from base to tip, and in
both a water-tight junction is obtained. Besides the central canal,
along which fluids are sucked up, there are lateral canals (tracheæ)
filled with air.
Réaumur was careful to correct his anatomical studies by close
observation of the live insect. He reared an angle-shades moth, which
he kept several days without food. When he saw it repeatedly extending
its proboscis, he put near it a piece of sugar. The moth at once
began to suck, and became so absorbed in satisfying its hunger that
it allowed Réaumur to carry it on a sheet of paper to a window and to
examine it closely with a lens. The proboscis was sometimes extended
for several minutes at a time, and then rolled up for an instant; its
tip was either employed in exploring the surface or closely applied to
the sugar. By means of the lens a slender column of liquid was seen to
pass along the central canal towards the head. Now and then, however, a
limpid fluid was seen to pass down the proboscis; this was the saliva
which was used to moisten the sugar, and then sucked up again.
The Budding-out of New Animals (Hydra): another Form of Propagation
without Mating (Aphids).
In the year 1744 a young Genevese, Abraham Trembley, tutor in the
family of Bentinck, who was then English resident at the Hague, rose
into sudden fame by a solid and well-timed contribution to natural
history. Trembley and his pupils used to fish for aquatic insects in
the ponds belonging to the residence, and in the summer of 1740 he
happened to collect some water-weeds, which he put into a glass vessel
and set in a window. When the floating objects had come to rest, a
small green stalk, barely visible to the naked eye, was found attached
to one of the plants. From one end of the stalk filaments or tentacles
were seen to project, and these moved slowly about. When the vessel was
shaken the stalk and tentacles contracted, but soon extended themselves
again. Was this object a plant or an animal? Its shape and colour were
those of a plant, and sensitive plants were known which drooped when
touched or shaken. Further observation showed that it could move from
place to place, which favoured the animal interpretation. Trembley
determined to cut the stalk in two; if the halves lived when separated
the fact would favour the plant-theory. The halves at first gave no
signs of life beyond occasional contraction and expansion, but after
eight days small prominences were seen on the cut end of the basal
half. Next day the prominences had lengthened; on the eleventh day they
seemed to be growing into tentacles. Before long eight fully formed
tentacles were visible, and Trembley had two complete specimens in
place of one; both were able to move about.
After four years of observation a handsome quarto volume was published,
which told the history of "The freshwater Polyp," a name suggested
by Réaumur; the Latin name of Hydra was given by Linnæus. Hydra
had been discovered and slightly described forty years before by
Leeuwenhoek, who had seen two young polyps branching from one parent
and spontaneously becoming free. Trembley made out all that a simple
lens, guided by a skilful hand and a keen eye, could discover. Thirteen
plates were admirably engraved by another amateur, Pierre Lyonet,
who was in all respects a fit companion for Trembley. It was proved
that Hydra preyed upon living animals, especially upon the Daphnia
or water-flea. When it was well nourished it branched spontaneously
again and again, forming a compound mass made up of scores or even
hundreds of polyps, all connected with a single base. The power of
locomotion and the power of devouring prey were held to settle the
animal nature of Hydra, a decision to which zoologists have ever since
adhered. Lyonet went on to try the effect of division upon some common
freshwater worms, and found that each part grew into a complete worm.
Artificial division is not indispensable; in the worm called Nais
division takes place spontaneously at certain seasons, one segment
dividing repeatedly, so as to form the segments of a complete new
individual. The process may be repeated until a chain of worms is
produced, which at length breaks up.[14]
A nail was thus driven in a sure place. The conception of an animal was
enlarged, for it was shown that an animal may branch and multiply in
a way hitherto supposed to be peculiar to plants. The old connecting
links between animals and plants (zoophytes, sponges, etc.) had never
been really investigated; no one knew what sort of organisms formed or
inhabited their plant-like skeletons. But Hydra, thanks to Trembley's
description, furnished a clear example of an animal which possessed
some of the attributes of a plant. Forms more ambiguous than Hydra,
such as Volvox and Euglæna, were ultimately to make the distinction
between animal and plant very uncertain and shadowy. It was Hydra that
gave the first clue to the structure of the zoophytes, and dispelled
the false notion that corals are plants, bearing flowers, fruits, and
seeds.
[11] By associating with them a number of alien genera.
[12] The third kingdom of nature was taken from the alchemists.
[13] The binomial nomenclature had been gradually coming in ever since
the time of the Bauhins.
[14] This discovery is usually attributed to Bonnet, but the testimony
of Réaumur (_Hist. des Insectes_, Vol. VI., p. lvi.) and of Trembley
(_Hist. des Polypes d'eau douce_, p. 323) is decisive in favour of
Lyonet.
Baer[15] has remarked that Trembley's discovery appreciably modified
the teaching of physiology by showing that an animal without head,
nerves, sense-organs, muscles, or blood may perceive, feed, grow, and
move about.
At the time when Trembley was demonstrating the asexual propagation of
Hydra, Bonnet (supra, p. 45) was demonstrating the asexual propagation
of aphids. Both naturalists were natives of Geneva, and both, as well
as their associate Lyonet, were in a sense pupils of Réaumur, who
not only set them an admirable example, but directed their attention
to promising researches and discussed with them the conclusions
which might be drawn. Réaumur's experience had seemed to confirm
Leeuwenhoek's statement (supra, p. 34) that aphids produce young
alive, even though no males are to be found among them; but unlucky
accidents defeated his intention to confirm it by experiment, and when
Bonnet asked him to suggest a piece of work Réaumur gave him the aphid
problem.[16]
Bonnet filled a flower-pot with moist earth, introduced a food-plant
together with a single new-born aphid, and covered all up with a
bell-jar. In twelve days the aphid produced its first young one; in
a month ninety-five had been born from the same unfertilised parent.
As many as five generations were obtained without the intervention of
a male, each successive parent having been isolated from the moment
of its birth. It was, however, discovered, apparently by Lyonet, that
though viviparous reproduction without males went on regularly so long
as food was plentiful, males appeared towards the end of summer, and
fertilised the eggs which were destined to outlast the winter.
The aphids added a new and peculiar example to the known cases of
asexual propagation (plants and Hydra). Much discussion followed, but
the physiology of that age (and the same is true of the physiology of
our own age) was unable to reveal the full significance of the observed
facts. Insects have since furnished many instances of unfertilised eggs
which yield offspring. One such instance was already recorded, though
neither Leeuwenhoek, Réaumur, nor Bonnet knew of it. In the year 1701
Albrecht of Hildesheim placed a pupa in a glass vessel and forgot it.
A moth hatched out and laid eggs, from which a number of caterpillars
issued.
Lyonet, whom we have more than once had occasion to mention, afterwards
became celebrated as the author of one of the most laborious and
beautiful of insect-monographs. The structure of the larva of the
goat-moth was depicted by him in eighteen quarto plates, crowded with
detail.
The Historical or Comparative Method: Montesquieu and Buffon.
About the middle of the eighteenth century we remark the introduction
of a new, or almost new, method of investigation, which was destined to
achieve great results. Hitherto many men had been sanguine enough to
believe that they could think out or decide by argument hard questions
respecting the origin of what they saw about them. It was easier, but
not really more promising, to resort to ancient books which contained
the speculations of past generations of thinkers. Now at last men
set themselves to study what is, and by the help of historical facts
to discover _how it came to be_. The new method was first applied
to the institutions of human society, but was in the end extended to the
earth, life on the earth, and a multitude of other important subjects.
Most writers call this method _historical_, because history is
the chief means by which it seeks to trace causes. Others call it
_genetic_, because it goes back, whenever it can, to origins. It
might also be called _comparative_, because it compares, not only
things which are widely separated in time, but also things which are
separated in space, things which differ in form or tendency because
they have a common origin, and things which differ in origin because
they have a common form or tendency. Whether the institutions, arts,
and usages of mankind, or the species of plants and animals, are in
question, the study of history, together with the comparative study of
what now exists, results in increased attention to development, and
this again brings to light the continuity of all natural agents and
processes—continuity in time and continuity among co-existences. Since
the new method has succeeded in tracing the causes of many phenomena
which once seemed to obey no law, it has done much to strengthen the
belief in universal causation.
Down to the middle of the eighteenth century the book of Genesis had
been almost unanimously accepted in Europe as the only source of
information concerning the origin of the world, of man, of languages,
of arts and sciences. The whole duration of the world was restricted
to so brief a space that slow development was impossible, and it was
assumed that early history of every kind must be miraculous.[17]
Montesquieu (_Esprit des Lois_, 1748) was the first to exhibit on
an impressive scale the power of the historical method. Natural
development, determined by unalterable conditions, was with him the
key to the right understanding of the past. It is well known that here
and there a great thinker had before Montesquieu framed something like
the same conception. The Politics of Aristotle[18] and Vico's study
of the historical evolution of the Roman law (1725) are memorable
anticipations. By 1748, the date of the _Esprit des Lois_, or 1749,
the date of Buffon's first volumes, which come next before us, Newton's
_Principia_ had made students of physics and astronomy practically
familiar with the notion of universal causation.
Buffon's place in the history of science is that of one who
accomplished great things in spite of weaknesses peculiarly alien to
the scientific spirit. It was mainly he who, by strenuous exertions
and largely at his own cost, transformed the gardens from which the
king's physicians used to procure their drugs into what we now know
as the Jardin des Plantes. By the untiring labours of fifty years he
produced a Natural History in thirty-six volumes crowded with plates.
Having won for himself a place side by side with Montesquieu and
Gibbon, he employed it to direct attention to the larger questions of
biology and geology. He was a pronounced freethinker, who promulgated
bold views with a dexterity which saved him from condemnation by the
theological tribunals. When his opinions were declared to be contrary
to the teaching of the Church, he printed a conciliatory explanation,
but never cancelled the passages objected to, which continued to appear
in a succession of editions. His deficiencies, we must admit, were
serious. He was a poor observer (partly because of short sight), and
had no memory for small details. His enemies were able to taunt him
with absurd mistakes, such as that cows shed their horns. He alienated
the two foremost naturalists of the eighteenth century, Linnæus and
Réaumur, by ignorant and scornful criticisms. His strong propensity
to speculation, insufficiently checked by care to verify, might have
brought him under the sarcastic remark of Fontenelle, that ignorance
is less apparent when it fails to explain _what is_, than when it
undertakes to explain _what is not_.
Buffon's fame is not seriously impaired by the fact that his great work
is no longer read except by those who study the course of scientific
thought. Few productions of the human intellect retain their value
after a hundred years, and scientific treatises become obsolete sooner
than others. It is consoling to recollect that, if their energy is
quickly dissipated, it is at least converted into light.
In a history of biology Buffon is naturally a more important figure
than Montesquieu. Buffon had imbibed evolutionary views from the
_Protogæa_ of Leibnitz, which in turn made use of certain hypotheses
of Descartes.[19] The _Histoire Naturelle_ inclines to some theory of
evolution, especially in the later volumes. At first Buffon teaches
that species are fixed and wholly independent of one another; some
years later he is ready to believe that all quadrupeds may be derived
from some forty original forms, while in a third and subsequent passage
he puts the question whether all vertebrates may not have had a common
ancestor. He does not shrink from saying that one general plan of
structure pervades the whole animal kingdom—a belief that he could
never have adequately supported by facts; Baer long afterwards (1828)
searched in vain for evidence on this very point, while Darwin in
1859 admitted that his arguments and facts only proved common descent
for each separate phylum of the animal kingdom;[20] he inferred _from
analogy_ that probably all the organic beings which have ever lived on
this earth have descended from some one primordial form.[21] Elsewhere
Buffon makes bold to declare that Nature in her youthful vigour threw
off a number of experimental forms of life, some of which were approved
and adopted, while others were allowed to survive in order to give
mankind a wider conception of her projects. There is generally some
gleam of truth in Buffon's most fantastic speculations, but we often
wish that he could have attended to the warning of Bossuet: "Le plus
grand dérèglement de l'esprit est de croire les choses parce qu'on veut
qu'elles soient."
[Illustration: GEORGES LOUIS LECLERC, COMTE DE BUFFON.]
Against all his shortcomings we must set the fact that Buffon strove
to interpret the present by the past, the past by the present, geology
by astronomy, geographical distribution by the physical history of the
continents. One of his maxims expresses the fundamental thought of
Lyell's _Principles of Geology_: "Pour juger de ce qui est arrivé,
et même de ce qui arrivera, nous n'avons qu'à examiner ce qui arrive."
Hard-and-fast distinctions are the marks of imperfect theory. Early
philosophers distinguished hot and cold, wet and dry, light and dark,
male and female, as things different in kind. In later times organic
and inorganic, animal and vegetable, the activities of matter and the
activities of mind, have been sharply separated. But as knowledge
increases these distinctions melt away; it is perceived that the
extreme cases are either now connected by insensible gradations, or
else spring historically from a common root. Hutton, Lyell, and their
successors have made it clear that the history of the earth calls for
no agents and no assumptions beyond those that are involved in changes
now going on; the present is heir by unbroken descent to the past.
Continuity has been established between all forms of energy. Even the
chemical elements, once the emblems of independence, give indications
that they too had a common origin. The nebular hypothesis, which has
been steadily rendered more probable by the scientific discoveries of
two centuries, traces all that can be perceived by the senses to a
homogeneous vapour, and lays the burden of proof on those who believe
that continuity has its limits. Every history, whether of planetary
systems, or of the earth's crust, or of human civilisations, religions,
and arts, is recognised as a continuous development with progressive
differentiation.
Amateur Students of Living Animals.
A history of biology would be incomplete which took no notice of
every-day observations of the commonest forms of life. Some of the best
are due to the curiosity of men with whom natural history was no more
than an occasional recreation. William Turner (a preacher, who became
Dean of Wells), Charles Butler (a schoolmaster), Caius and Lister
(physicians), Claude Perrault (a physician and architect), Méry and
Poupart (surgeons), Frisch (a schoolmaster and philologue), Lyonet (an
interpreter and confidential secretary), Roesel (a miniature painter),
Henry Baker (a bookseller, who gained a competence by instructing deaf
mutes), Leroy (ranger to the King of France), Stephen Hales, Gilbert
White and William Kirby (country parsons), and William Spence (a
drysalter) were all amateurs in natural history. To this list we might
add Willughby, Ray, Leeuwenhoek, Réaumur, De Geer, Buffon, the Hubers,
and George Montagu, who were either so fortunate in their worldly
circumstances or so devoted to science as to make it their chief, or
even their sole pursuit, though they did not look to it for bread.
A large proportion of the naturalists whose names have been quoted
occupied themselves with the habits and instincts of animals, and
biology has been notably enriched by their observations. To Englishmen
the most familiar name is that of Gilbert White, in whom were combined
thirst for knowledge, exactness in description, and a feeling for the
poetry of nature.
White used his influence to encourage what may be called _live natural
history_, which, as he understood it, "abounds in anecdote[22] and
circumstance." He bids his correspondents to "learn as much as possible
the manners of animals; they are worth a ream of descriptions." His
example has done more than his exhortations. He focusses a keen
eye upon any new or little-known animal, such as the noctule, the
harvest-mouse, or the mole-cricket; detects natural contrivances
little, if at all, noticed before, such as the protective resemblance
of the stone-curlew's young; dwells upon the practical applications
of natural history, such as the action of earthworms in promoting
the fertility of soils; and combines facts which a dull man would be
careful to put into separate pigeon-holes, such as the different ways
in which a squirrel, a field-mouse, and a nuthatch extract the kernels
of hazel-nuts.
The many amateurs of the eighteenth century naturally demanded books
written to suit them, and illustrated books with coloured plates,
coming out in parts, found a ready sale. Some were devoted to insects,
others to microscopic objects. In accordance with prevalent belief, the
writers made a point of tracing the hand of Providence in the minutest
organisms; many popular treatises were altogether devoted to natural
theology. Some few of these natural history miscellanies contained
original work, which has not yet lost its interest. The best is
Roesel's _Insecten-belustigungen_ (four vols. 4to., 1746-61),
memorable among other things for containing the original description of
Amœba. For English readers Henry Baker wrote _The Microscope Made
Easy_ (1743) and _Employment for the Microscope_ (1753).
Intelligence and Instinct in the Lower Animals.
The period with which we are now concerned (1741-1789) initiated the
profitable discussion of the mental powers of animals. We are unable
for lack of space to follow the investigation from period to period,
and must condense into one short section whatever its history suggests.
In the year 1660 Aristotelians were still discoursing about the
vegetative and sensitive souls which bridged the gulf between inanimate
matter and the thinking man. Descartes had tried to prove that the
bodies of men and animals are machines actuated by springs like
watches. Man, however, according to Descartes, possesses a soul wholly
different in its properties from his body, and apparently incapable of
being acted upon by it. Man only can think; animals are capable only
of physical sensations, and have no consciousness. Into speculations
like these we shall not venture, being- content, like Locke, "to sit
down in quiet ignorance of those things which upon examination are
proved to be beyond the reach of our capacities." We shall merely note
here and there facts ascertained by observation or experiment, and
plain inferences drawn from such facts.
Swammerdam and Réaumur, besides many naturalists of less eminence,
recorded a host of observations on the activities of insects. They
contributed little to the discussion except new facts, for habit led
them to ascribe without reflection every contrivance to the hand of
Providence or else to Nature. Some of their facts, however, made a
deep impression, none more than the exact agreement of the cells
of the honeycomb with the form which calculation showed to be most
advantageous.[23] The coincidence has lost some of its interest since
the discovery that the theoretically best form of cell is hardly ever
realised.[24] Réaumur,[25] in describing the process by which a certain
leaf-eating caterpillar makes a case for itself out of the epidermis
of an elm-leaf, showed that the caterpillar is not devoid of that kind
of intelligence which adapts measures to circumstances. He cut off the
margin where the upper epidermis of the leaf passes into the lower
one, a margin which the insect had intended to convert into one side
of its case; the caterpillar sewed up the gap. He cut off a projection
which was meant to form part of the triangular end of the case; the
caterpillar altered its plan, and made that the head-end which was
originally intended to lodge the tail. This observation anticipates a
better-known example taken from the economy of the hive-bee by Pierre
Huber, which is mentioned below.
Buffon[26] heard with impatience all expressions of admiration for
the works of insects. His poor eyesight and his repugnance to minutiæ
disinclined him to pay much attention to creatures so small, and he had
set himself up as the rival of Réaumur in physics and natural history.
To pour contempt upon insects gratified both feelings at once. Bees, he
said, show no intelligence at all; their actions are purely automatic,
and their much-vaunted architecture is merely the result of working in
a crowd. The cells of the honeycomb are hexagonal, not by reason of
forethought or contrivance, but because of mutual pressure; soaked peas
in a confined space form hexagonal surfaces wherever they touch.
The elder Huber seems to have denied to bees every trace of
intelligence, but his son Pierre found it hard to go so far.[27] He
remarked that the storage-cells of a honeycomb are not always exactly
alike; they may be lengthened, cut down, or curved, when requisite.
Cells which had been rudely trimmed with a knife were repaired with
such dexterity and concert as to suggest that even the hive-bee has
"le droit de penser." Bees would under compulsion build upwards or
sideways, instead of downwards, as they like to do. Finding that they
sought to extend their combs in the direction of the nearest support,
he covered the support with a sheet of glass, on which they could get
no footing. They swerved at once from the straight line, and prolonged
their comb towards the nearest _uncovered_ surface, though this obliged
them to distort their cells. He was driven to the conclusion that bees
possess "a little dose of judgment or reason." In our own time, when
all conscious adaptation of means to ends is believed to be worthy of
the name of _reason_, it requires no great courage to ask why we deny
such an attribute to all the lower animals.
In spite of examples like this, the favourite expression "blind
instinct" helped to strengthen the conviction that the mental processes
of animals are unsearchable. It is impossible to deny that the epithet
_blind_ is appropriate in many cases. A bird will sit an addled egg
all summer, or vainly but repeatedly attempt to make its tunnel in the
insufficient breadth of a mud wall (Geositta). Of course such instances
do not show that _all_ the acts of the lower animals are devoid of
intelligence.
Hume in 1739 and again in 1748 appealed to everyday observation of
dogs, birds, and other animals of high grade. The facts seemed to him
to show that animals as well as men are endowed with reason and able
to draw inferences; he did not, however, credit them with the power of
framing general statements, holding that experience operates on them,
as on children and the generality of mankind, by "custom" alone. It is
notorious that the dog and other higher animals learn by experience;
Hume tells, for instance, how an old greyhound will leave the more
fatiguing part of the chase to younger dogs, and place himself so as
to meet the hare in her doubles. On the other hand (though Hume does
not say so) man himself possesses non-educable instincts. In short,
Hume sees no ground for drawing a line between the mental powers of man
and those of the higher animals, though he attributes to man a power
of demonstrative reasoning to which animals do not attain. In this he
substantially agrees with Aristotle,[28] who maintained that in animals
the germs of the psychical qualities of the man are evident, though,
as in the child, they are undeveloped. Hume's teaching also accords
with modern views; comparative anatomy, for instance, "is easily able
to show that, physically, man is but the last term of a long series of
forms, which lead by slow gradations from the highest mammal to the
almost formless speck of living protoplasm, which lies on the shadowy
boundary between animal and vegetable life."[29]
The detailed proofs which Hume was not enough of a naturalist to
furnish were at length stated with admirable clearness and force by
Leroy, whose _Letters on Animals_ form the most important contribution
made to the discussion during our period. Georges Leroy ( 1723-1789)
was _lieutenant des chasses_ under the last French kings, and had
charge of the parks at Versailles and Marly. He wrote therefore with
knowledge about the wolf, fox, deer, rabbit, and dog. His pages are
enlivened by many touches of nature, interesting to readers who perhaps
care little about psychology. Leroy attributes to the wolf observation,
comparison, judgment. The wolf must mark the height of the fold which
encloses a flock, and judge whether he can clear it with a sheep in his
mouth. Wolf and she-wolf co-operate artfully in the running-down of
prey. Sometimes the she-wolf will draw off the sheep-dog in pursuit,
thus putting the flock at the mercy of her mate. Or one of the two will
chase the quarry till it is out of breath, when the other can take up
the running on advantageous terms. An old fox shows knowledge of the
properties of traps, and will rather make a new outlet or suffer long
famine than encounter them. But when he finds a rabbit already caught,
he realises that the trap has lost its power to hurt. Sheep-dogs can
be educated to mind things which do not interest wild dogs, or dogs of
other breeds; when, for instance, the flock is driven past a patch of
wheat, the dog in charge will take care that the sheep do not damage
the crop. A trained sporting-dog learns at length to trust his own
judgment, even in opposition to that of his master, and sportsmen
know that they must direct young dogs, but leave old ones to act for
themselves.
From the middle of the eighteenth century to the present day
naturalists and psychologists have been labouring to distinguish
instinct from intelligence. It is not hard to define well-marked
examples of each, and to show that a typical instinct is _congenital_
(not the result of a process of education or self-education),
_adaptive_ (conducive to the welfare of the organism), _co-ordinated
by nerve-centres_ (thus excluding the superficially similar behaviour
of the lowest animals and all plants), _actuating the whole organism_
(thus excluding most, if not all, reflex acts in the higher animals,
as well as the wonderful adjustments effected by bone-corpuscles
and other parts of organisms), and _common to all the members of a
species or other group_ (thus excluding individual aptitudes).[30]
In the same way it is easy to point out clear differences between a
bird and a tree. But just as a definition which shall separate every
animal from every plant has hitherto been sought in vain, so it has
hitherto been impossible to frame a definition which while including
all instincts shall admit no case of reflex action or intelligence. The
most ambiguous cases of all are perhaps to be found in insects, where,
as will shortly be explained, our information is ill-fitted to support
precise distinctions.
Many naturalists entertain some form of what may be called the
_use-and-disuse_ or _inherited-memory_ theory, supposing that
the aptitudes of the offspring are influenced by the activities of
the parent. Some cling to the belief that habits can be fixed and
transmitted, and we must admit that the fixation and transmission of
habits might explain a great deal. But all the evidence goes to prove
that habits are not inherited at all, and that we must look elsewhere
for the origin of instincts. Let naturalists who think differently try
to account for the instincts of working bees or ants, which receive
their psychical not less than their physical endowment from a long
succession of ancestors, none of which worked for their living. Or let
them try to explain the instances of spiders, insects, etc., which
_after egg-laying_ practise instinctive arts for the defence of
their brood, standing over the eggs, carrying them about, blocking the
entrance of the burrow, etc. May we not say that it is impossible for
the acts of a parent to influence the congenital instincts of offspring
which have already lost connection with the mother? But surely a theory
of instinct breaks down which fails to account for the expedients by
which the worker-bee, the worker-ant, and the spider provide for the
safety of the unhatched brood or for the welfare of the community.
Darwin's _Origin of Species_ threw a new light upon instinct
by showing that natural selection can operate on the subtlest
modifications. It can discriminate shades of hardiness to climate,
shades of intellectual acuteness, or shades of courage. It can
intensify qualities which appear only in adults past bearing or in
individuals congenitally incapable of propagation. Human selection,
though a blunt tool in comparison with natural selection, can originate
a bold and hardy race of dogs, or showy double flowers incapable of
producing seed. In the second case fertile single flowers continue the
race, as in the garden Stock. Darwin pointed out that the barren double
flowers of the Stock answer to the workers of social bees and ants,
the fertile single flowers to the functional males and females. Every
modification that works to the advantage or disadvantage of the race,
whether we classify it as physical, intellectual, or moral, gives scope
for the operation of natural selection.
The comparative psychology of small invertebrates, such as insects,
is impeded by our imperfect knowledge of their nervous physiology.
Introspection is here impossible; experimental physiology and
pathology, which have done so much for the psychology of the higher
vertebrates, almost impossible; analogy is a treacherous guide where
the structures involved differ conspicuously. We have little to guide
us in the psychology of insects except their behaviour, and that is
often capable of a variety of interpretations. The only course is
to adopt Pasteur's watchword, "Travaillons!"—the difficulties will
diminish with time and labour.
The Food of Green Plants.
Common observation taught men in very early times that green plants
draw nourishment from the soil, and that sunlight is necessary to
their health. In the age of Galileo a Belgian physician and chemist,
Van Helmont, endeavoured to pursue the subject by experiment. He
planted the stem of a live willow in furnace-dried earth, which was
enclosed in an earthen vessel. Rain-water or distilled water was
supplied when necessary, and dust excluded by a perforated lid. The
loss of weight due to the falling-off of leaves was neglected. In
the course of five years the tree was found to have increased to
more than thirty times its original weight; Van Helmont concluded
that this increase was due to water only. Malpighi (1671), being
guided mainly by his microscopic studies of the anatomy of the stem
and leaf, taught that moisture absorbed by the roots ascends by the
wood, becoming (apparently at the same time) aerated by the large,
air-conducting vessels; that it enters the leaves, and is there
elaborated by evaporation, the action of the sun's rays, and a process
of fermentation; lastly, that the elaborated sap passes from the leaves
in all directions towards the growing parts. It will be seen that this
explanation, though incomplete, makes a fair approximation to the
beliefs now held; for more than a hundred years after Malpighi's day
less instructed opinions were commonly held. Hales (1727) recognised
that green plants are largely nourished at the expense of the
atmosphere; he dwelt also on the action of the leaves in drawing water
from the soil, and in discharging superfluous moisture by evaporation.
Joseph Priestley, who had been proving that air is necessary both to
combustion and respiration, made an experiment in 1771 to discover
whether plants affected air in the same way that animals do. He put
a sprig of mint into a vessel filled with air in which a candle had
burned out, and after ten days found that a candle would now burn
perfectly well in the same air. Air kept without a plant, in a glass
vessel immersed in water, did not regain its power of supporting
combustion. Balm, groundsel, and spinach were found to answer just as
well as mint. Air vitiated by the respiration of mice was restored by
green plants as readily as air which had been vitiated by combustion.
Priestley did not remark that the glass vessels employed in his
experiments had been set in a window, and inattention to this point
caused some of his attempts to repeat the experiment to fail. He was
further perplexed by using vessels which had become coated with a film
of "green matter," probably Euglæna. Such vessels restored vitiated
air, though no leaves were present, and when placed in the sun, gave
off considerable quantities of a gas, Priestley's "dephlogisticated
air" (oxygen). Hardly any oxygen was given off when the green matter
was screened by brown paper. Water impregnated with carbonic acid
was found to favour the production of the green matter. To us,
who have been taught at school something about the properties of
green plant-tissues, it seems obvious that Priestley ought to have
ascertained by microscopic examination whether his "green matter"
was not a living plant. But he had always avoided the use of the
microscope, his eyes being weak, and after some imperfect attempts
in this way he made up his mind that the green matter was neither
animal nor vegetable, but a thing _sui generis_. Neglecting his
most instructive experiments, and not waiting till he could devise new
ones, or even disentangle his thoughts, he sent to the press a confused
explanation, which seemed to teach that vitiated air may be restored by
sunlight alone.
A Dutch physician, named John Ingenhousz, who was then living in
England, read Priestley's narrative and began to investigate on his own
account. Without detailing his numerous experiments, we may give his
own clear summary (condensed). "I observed," Ingenhousz says, "that
plants have a faculty to correct bad air in a few hours; that this
wonderful operation is due to the light of the sun; that it is more
or less brisk according to the brightness of the light; that only the
green parts of the plant can effect the change; that leaves pour out
the greatest quantity of oxygen from their under surfaces; that the sun
by itself has no power to change the composition of air." It will be
seen that Priestley started the inquiry, devised and executed the most
necessary experiments, and got excellent results. Then he lost his way,
and bewildered by conflicting observations, which he was too impatient
to reconcile, published a barren and misleading conclusion. Nothing was
left for him but to acknowledge that Ingenhousz had cleared up all his
perplexities.
Nicholas Theodore de Saussure, son of the Alpine explorer, showed in
1804 that when carbon is separated from the carbonic acid of the air
by green plants, the elements of water are also assimilated, a result
which owes its importance to the fact that starch is a combination of
carbon with the elements of water. Saussure also proved that salts
derived from the soil are essential ingredients of plant-food, and that
green plants are unable to fix the free nitrogen of the air; all the
nitrogen which they require is obtained from the ground.
We are unable to follow the history further. Though the main facts
were established as early as the beginning of the nineteenth century,
experimental results of scientific and practical interest have never
ceased to accumulate down to the present time.
The Metamorphoses of Plants.
Speculations concerning the nature of the flower roused at one time
an interest far beyond that felt in most botanical questions. The
literary eminence of Goethe, who took a leading part in the discussion,
heightened the excitement, and to this day often prompts the inquiry:
What does modern science think of the Metamorphoses of Plants?
Let us first briefly notice some anticipations of Goethe's famous
essay. In the last years of the sixteenth century Cesalpini, taking
a hint from Aristotle, tried to establish a relation between certain
parts of the flower and the component layers of the stem. Linnæus
worked out the same notion more elaborately, and with a confidence
which sought little aid from evidence. His wonderful theory of
Prolepsis (Anticipation) need not be described, far less discussed,
here. He also borrowed and adapted an analogy which had been thrown
out by Swammerdam. The bark of a tree, which according to the theory
of Prolepsis gives rise to the calyx of the flower, he compared to the
skin of a caterpillar, the expansion of the calyx to the casting of
the skin, and the act of flowering to the metamorphosis by which the
caterpillar is converted into a moth or butterfly. More rational than
the speculations just cited, and more suggestive to the morphologists
of the future, are his words: "Principium florum et foliorum idem
est" (Flower and leaf have a common origin)—which was not, however,
a very novel remark in the eighteenth century. Long before Linnæus
early botanists had remarked the resemblance of sepals, petals, and
seed-leaves to foliage-leaves; Cesalpini has a common name for all
(folium).
At the very time when Linnæus was occupied with his fanciful analogies,
a young student of medicine named Caspar Friedrich Wolff, who was
destined to become a biologist of great note, published a thesis
which he called _Theoria Generationis_ (Halle, 1759). This thesis
marks an epoch in the history of animal embryology, but what concerns
us here is that Wolff examined the growing shoot, and there studied
the development of leaf and flower. He found that in early stages
foliage-leaves and floral-leaves may be much alike, and thought that he
could trace both to a soft or even fluid substance, which is afterwards
converted into a mass of cells. It seemed to him possible to resolve
the flowering shoot into stem and leaves only. Wolff's thesis, or at
least that part of it which dealt with the plant, was little read and
soon forgotten; his studies of the development of animals were carried
further and became famous.
Goethe in 1790 revived Wolff's theory of the flower, without suspicion
that he had been anticipated. It is only our ignorance, he said, when
the fact came to his knowledge, that ever deludes us into believing
that we have put forth an original view. As soon as he realised the
true state of the case, he spared no pains to do Wolff full justice.
The aim of Goethe's _Metamorphoses of Plants_ was to determine the
Idea or theoretical conception of the plant, and also to trace the
modifications which the Idea undergoes in nature. These two inquiries
constituted what he called the Morphology of the plant, a useful,
nay, indispensable term, which is still in daily use. He thought
that he could discover in the endless variety of the organs of
the flowering plant one structure repeated again and again, which
gradually attained, as by the steps of a ladder, what he called the
crowning purpose of nature—viz., the sexual propagation of the race.
This fundamental structure was the leaf. The proposition that all the
parts of the flower are modifications of the leaf he defended by three
main arguments—viz., (1) the structural similarity of seed-leaves,
foliage-leaves, bracts, and floral organs; (2) the existence of
transitions between leaves of different kinds; and (3) the occasional
_retrogression_, as he called it, of specially modified parts to a
more primitive condition. These lines of argument were illustrated by
many well-chosen examples, the result of long and patient observation.
Goethe did not, however, fortify his position by the likeness of
developing floral organs to developing foliage-leaves, which had been
Wolff's starting-point. He arrived independently at Wolff's opinion
that the conversion of foliage-leaves into floral organs is due to
diminished nutrition.
Linnæus's exposition of the nature of the flower had been read
attentively by Goethe, who must have remarked that the conversion of
organs to new uses was there described as a _metamorphosis_. That
word had been, long before the time of Linnæus, appropriated to a
particular kind of change—viz., an apparently sudden change occurring
in the life-history of one and the same animal. It was therefore unlucky
that Goethe should have been led by the example of Linnæus to employ the
word in the general sense of adaptation to new purposes. He did not,
however, expressly compare flower-production with the transformation of
an insect, as Linnæus had done.
The reception of Goethe's _Metamorphosen der Pflanzen_ was at first
cold, but the doctrine which it enforced gradually won the attention of
botanists, and by 1830 he was able to show that it had been accepted by
many good judges.
Then came the discoveries of Hofmeister, followed by Darwin's _Origin
of Species_. Naturalists soon ceased to put the old questions, and
the old answers did not satisfy them. Wolff and Goethe had generalised
the flowering plant until it became a series of leaf-bearing nodes
alternating with internodes, but no such abstract conception could
throw light upon the common ancestor of all the flowering plants,
nor upon the stages by which the flowering plant has been evolved,
and it was these which were now sought. Hofmeister brought to light
a fundamental identity of structure in the reproductive organs of
the flowering plants and the higher cryptogams. There has since
been no doubt in what group of plants we must seek the ancestor of
the flowering plant. It must have been a cryptogam, not far removed
from the ferns, and furnished with _sporophylls_—_i.e._,
leaf-like scales, on which probably two kinds of sporangia, lodging male
and female spores respectively, were borne. The careful investigation of
the fossil plants of the coal measures has brought us still nearer
to the actual progenitor. Oliver and Scott[31] have pointed out that
the carboniferous Lyginodendron, though showing unmistakable affinity
with the ferns, bore true seeds, as a pine or a cycad does. Many other
plants of the coal measures are known to have combined characteristics
of ferns with those of cycads, while some of them, like Lyginodendron,
crossed the frontier, and became, though not yet flowering plants, at
least seed-bearers.
The discovery of a fossil plant which makes so near an approach to
the cryptogamic ancestor of all the flowering plants may remind us
how little likely it was that the ideal plant of Wolff and Goethe,
consisting of leaves, stem, and other vegetative organs, but without
true reproductive organs, should fully represent the type from which
the flowering plants sprang. No plant so complex as a fern could
maintain itself indefinitely without provision for the fertilisation of
the ovum; the only known asexual plants are of low grade, and, it may
be, insufficiently understood.
What substratum of plain truth underlies the doctrine of the
metamorphoses of plants? Botanists would agree that all sporophylls,
however modified, are homologous or answerable parts. Carpels and
stamens are no doubt modified sporophylls. Petals are sometimes,
perhaps always, modified stamens, and therefore modified sporophylls
also. We must not call a sporophyll a _leaf_, for it contains a
sporangium of independent origin, and the sporangium is the more
essential of the two. The common origin of foliage-leaf, bract,
perianth-leaf, sporophyll (apart from the sporangium), and seed-leaf
is unshaken. We may picture to ourselves a plant clothed with nearly
similar leaves, some of which either bear sporangia or else lodge
sporangia in their axils. Part of such a primitive flowering plant
might retain its vegetative function and become a leafy shoot,
while another part, bearing crowded sporophylls, might yield male,
female, or mixed cones. From an ancestor thus organised any flowering
plant might be derived. But the chief wonder of the theory of
Metamorphoses—viz., the derivation of stamen and pistil from mere
foliage-leaves—disappears. Anther and ovule take their real origin
from the sporangium, whose supporting leaf is only an accessory.
The chief steps by which the morphology of the flowering plant has
been attained are these:—Cesalpini (1583), followed by several other
early botanists, recognized the fundamental identity of foliage-leaf,
perianth-leaf, and seed-leaf. Linnæus (1759) added stamen and carpel
to the list, identifications of greater interest, but only partially
defensible. Wolff (1759) justified by similarity of development the
recognition of floral organs as leaves. Goethe (1790) traced structural
similarity, transitions, and retrogression in leaves of diverse
function. Hofmeister (1849-57) showed a relationship between the
flowering plant and the higher cryptogams. Oliver and Scott (1904),
inheriting the results of Williamson's work, discovered a carboniferous
seed-bearing plant, one of a large group intermediate between ferns and
cycads. It is now possible to explain the resemblance of the various
leaf-like appendages of the flowering plant by derivation either from
the leaves or the sporophylls (the latter not being wholly leaves) of
some extinct cryptogam, which was either a fern or a near ally of the
ferns.
Early Notions about the Lower Plants.
The fathers of botany neglected everything else in order to concentrate
their attention upon the flowering plants, from which very nearly
all useful vegetable products were derived. The lack of adequate
microscopes rendered it almost impossible to investigate the structure
and life-history of ferns, mosses, fungi, and algæ until the nineteenth
century. As late as the time of Linnæus it was possible to maintain
that they developed spontaneously, though the great naturalist himself
called them Cryptogamia, thereby expressing his conviction that they
reproduce their kind like other plants, but in a way so far not
understood. Gaertner, a contemporary of Linnæus, pointed out one
important respect in which the spores of cryptogams differ from the
seeds of flowering plants, viz. that they contain no embryo.
_Ferns._—Even before the age of Linnæus it was known that little
ferns spring up around the old ones, and that a fine dust can be shaken
from the brown patches on the back of ripe fern-leaves. The dust was
reputed to be the seed of the fern, and in an age which believed in
magic the invisibility of fern-seed made it easy to suppose that the
possessor of fern-seed would become invisible also. When the microscope
began to be applied to minute natural objects, the brown patches of the
fern-leaf were closely examined. William Cole of Bristol (1669),
Malpighi, Grew, Swammerdam, Leeuwenhoek, and others, found the stalked
capsules (sporangia), their elastic ring and the minute bodies (spores)
lodged within them; it seemed obvious to call the capsules ovaries and
the spores seeds. Some time in the latter part of the seventeenth
century Robert Morison, professor of botany at Oxford, who died in 1683,
sowed spores of the harts-tongue fern, and next year got an abundant
crop of prothalli, which he took to be the cotyledons. A little later,
when it had been proved that flowering plants possess male and female
organs, diligent search was made for the stamens and pistils of ferns
and mosses, which of course could not be found, though identifications,
sometimes based upon a real analogy, were continually announced. Late
in the eighteenth century one John Lindsay, a surgeon in Jamaica, who
was blest with leisure and a good microscope, repeated the experiment
of Morison, which seems to have been almost forgotten. Having remarked
that after the rains young ferns sprang up in shady places where the
earth had been disturbed. it occurred to him to mix the fine brown
dust from the back of a fern-leaf with mould, sow the mixture in a
flower-pot, and watch daily to see what might come up. About the
twelfth day small green protrusions were observed, which enlarged,
sent down roots, and formed bilobed scales, out of which young ferns
ultimately grew. In 1789 Sir Joseph Banks, who was reputed to be the
best English botanist of the day, asked Lindsay's help in sending West
Indian ferns to Europe. Lindsay replied that it would be easier to send
the seed, and that the seed would grow if properly planted. This was
new to Banks, who demanded further information. Lindsay then prepared a
short illustrated paper, which Banks communicated to the newly formed
Linnean Society. It will be seen that Lindsay was able to add nothing
of much importance to what Morison had ascertained a century before.
The spores were still identified with seeds, the prothallus was still
a cotyledon, and for years to come botanists continued to seek anthers
on fern-leaves. At this point we suspend for a time the history of the
discovery (see below, p. 108).
_Mosses._—Linnæus observed that the large moorland hair-moss
(Polytrichum) is of two forms, only one of which bears capsules, and
further that in dry weather the capsules emit masses of fine dust.
No further progress was made until 1782, when Hedwig, in a memoir of
real merit, described the antheridium and archegonium of the moss,
and traced the capsule to the archegonium. Interpreting the organs of
the moss by those of the flowering plant, he called the antheridia
anthers, the capsule was a seed-vessel, the spores were seeds, and
the green filament emitted by the germinating spore a cotyledon. Such
misinterpretations were then inevitable.
_Fungi._—Micheli in 1729 found the spores of several fungi,
germinated them, and figured the product. The figures show the
much-branched filament (mycelium) which burrows in the soil and
constitutes the vegetative part of the fungus, and also here and there
a pileus (mushroom, toadstool, &c.), which is the fructification
springing out of the mycelium. His account comprises the best part of
what is known down to the present time of the reproduction of that group
of fungi to which the mushroom belongs.
_Algæ._—Some early observers (Réaumur among the rest) studied the
enlarged and fleshy branches of brown seaweeds, and discovered the
seed-like spores.
This scanty knowledge of the life-history of cryptogams sufficed
until the nineteenth century, when the study was resumed with better
microscopes and in a far more connected way, with results of the
highest interest and importance (see below, p. 108).
[15] Reden, Vol. I., pp. 109, 154.
[16] _Traité d'Insectologie_, première partie. Two vols.12 mo. Paris,
1745.
[17] In circles untouched by general European thought such beliefs
lasted much later. Sir Francis Galton (_Memories of My Life_, p. 67)
says: "The horizon of the antiquarians was so narrow at about the
date (1840) of my Cambridge days that the whole history of the early
world was literally believed, by many of the best-informed men, to
be contained in the Pentateuch. It was also practically supposed
that nothing more of importance could be learnt of the origin of
civilisation during classical times than was to be found definitely
stated in classical authors."
[18] "If anything could disentitle Montesquieu's _Esprit des Lois_ to
the proud motto, _Prolem sine matre creatam_, it would be its close
relationship to the Politics." (A. W. Benn's _Greek Philosophers_, Vol.
II., p. 429.)
[19] For an account of other early hypotheses of the same kind the
reader may refer to Edward Clodd's _Pioneers of Evolution_.
[20] _Life and Letters_, Vol. II., p. 212.
[21] _Origin of Species_, ed. i., p. 484.
[22] White uses _anecdote_ in the old sense, meaning by it a piece of
unpublished information.
[23] Réaumur, _Hist. des Insectes_, Vol. V., Mém. viii.
[24] Darwin, _Origin of Species_, chap. vii.
[25] Vol. III., Mém. iv.
[26] _Hist. Nat._, Vol. IV.
[27] The first edition of the _Nouvelles Observations sur les Abeilles_
(1792) was the work of François Huber alone; the second (1814) was
prepared by Pierre with the co-operation of his father, and is here
credited to the son.
[28] _Hist. Animalium_, VIII., i.
[29] Huxley's _Hume_, chap. v. Some few naturalists, who are entitled
to respectful attention, such as Father Wasmann, author of _The
Psychology of Ants_, do not even now receive the conclusions of Hume.
[30] Lloyd Morgan, _Habit and Instinct_, Introduction.
[31] _Phil. Trans._, 1904.
PERIOD IV.
1790-1858
Characteristics of the Period.
The first French republic and the first French empire were associated
with a great outburst of scientific energy. French mathematics,
astronomy, and physics were pre-eminent. England suffered from
isolation during the continental war, but Davy, Young, the Herschels,
Watt (now past his prime), Dalton, and William Smith supported the
scientific reputation of their country. In Germany this was the age
of Goethe and Schiller; Alexander von Humboldt was prominent among
the scientific men of Prussia. The forty years' peace, during which
reaction prevailed in many parts of Europe, was in England and America
a time of steady growth and progress.
Sprengel and the Fertilisation of Flowers.
Conrad Sprengel, an unsuccessful schoolmaster who lived in a Berlin
attic and got his bread by teaching languages or whatever else his
pupils wished to learn, wrote a book which marks an epoch in the study
of adaptations. This was his _Secret of Nature Discovered_, which
appeared in 1793. Half a century passed before its merit was recognised
by any influential naturalist; even then the recognition was private,
and never reached the author, who had died long before. There was no
striking of medals, no jubilee-celebration, nothing more than this,
that Robert Brown recommended the book to Charles Darwin, who found in
it, as he says, "an immense body of truth."
In 1787 Sprengel had remarked that the bases of the petals of Geranium
silvaticum are beset with long hairs. Persuaded that no natural
structure can be devoid of meaning, Sprengel asked what purpose
these hairs might serve. A honey-gland in their midst suggested that
they might protect the honey by keeping off the rain, which easily
enters this shallow flower. Other honey-secreting flowers were found
to possess mechanisms adapted to the same end. His first question
suggested a second: Why should flowers secrete honey?
Malpighi had described the honey-glands of crown-imperial (1672),
and had seen that the honey must be secreted by the petals, and not
deposited from the atmosphere, according to the notion then current.
Kölreuter (1761) had showed that insects may effect the pollination
of flowers. Linnæus (1762) had given the name of _nectary_ to the
honey-gland. He thought that the honey served to moisten the ovary,
though he knew of staminate flowers furnished with nectaries. He
also threw out the alternative conjecture that the honey is food for
insects, which disperse the pollen by their wings. Sprengel improved
upon all his predecessors, and made it clear that transference of
pollen is the main purpose of the honey in flowers. He was put on the
right track by the study of a forget-me-not flower. Here he found the
honey protected from rain by the narrowness of the corolla-tube, whose
entrance was almost closed by internal protuberances. The protuberances
were distinguished by their yellow colour from the sky-blue corolla,
and this conspicuous colouration led Sprengel to infer that insects
might be thereby induced to seek for the store of honey within. He
tested his conjecture by examining other honey-bearing flowers, and
soon collected many instances of spots, lines, folds, and ridges,
which might not only make insects aware of hidden stores of honey, but
guide them to the exact place. Contrivances of the most diverse kinds,
but all tending to invite the visits of insects and utilise them for
the benefit of the plant, rewarded Sprengel's continued inquiries. He
found that night-flowering plants, which could derive no advantage from
coloured patterns, often have large white corollas, easily discerned
in a faint light, and that these flowers give out an odour attractive
to nocturnal insects. He found that the pollen-masses of an orchis
are actually removed by large insects, though here no honey could be
detected in the flower. Sprengel's fertility in probable conjecture
is shown by his explanation of this puzzling case; he suggested that
the orchis is a sham honey-bearer (Scheinsaftblume), which attracts
insects by assuming the conspicuous size and coloration found in most
honied flowers. Darwin suspected, and Herman Müller proved, that
though the spur of the orchis-flower is empty, it yields when pierced
a fluid attractive to bees and other insects. Sprengel discovered too
how insects get imprisoned in the corolla of an Aristolochia, whose
reflexed hairs allow small flies to creep in, but effectually prevent
their escape until they have fertilised the pistils, when the hairs
relax. These are only specimens of a multitude of adaptations which
fill the book.
Sprengel insists upon the study of flowers under natural conditions;
he could never have made out by the examination of plucked flowers
how Nigella is fertilised. Flies with attached pollen-masses, which
he found in spiders' nests, gave him the hint as to the way in which
the fertilisation of orchids is effected. Definite questions must
be put if observation is to be profitable. What is the use of honey
to the plant—of this coloured spot—of these hairs? He notes the
peculiarities of wind-fertilised and insect-fertilised flowers, the
relative abundance of the pollen, the form of the stigma, the presence
or absence of honey, the size, colour, and scent of the corolla. Here
is a pretty illustration from his pages. Pluck a branch of hazel,
aspen, or alder, with unexpanded catkins, and also one from the male
sallow; place them in water, and keep them in a sunny window until
the anthers are ripe. A vigorous puff will then discharge a cloud
of pollen from the _wind-fertilized_ catkins, but none from the
_insect-fertilised_ catkin of the sallow. What Linnæus said about
the flowers of trees appearing before the leaves, in order that the
pollen may more easily reach the stigmas, holds good, Sprengel remarks,
only of wind-fertilised trees. The lime, which is insect-fertilised,
flowers in the height of summer, when all the branches are crowded with
leaves.
Sprengel left it to later biologists to complete his discovery. "That
wonderfully accurate observer, Sprengel," says Darwin,[32] "who first
showed how important a part insects play in the fertilisation of
flowers, called his book _The Secret of Nature Displayed_; yet he
only occasionally saw that the object for which so many curious and
beautiful adaptations have been acquired, was the cross-fertilisation
of distinct plants; and he knew nothing of the benefits which the
offspring thus receive in growth, vigour, and fertility." Not even
Cuvier and the Rise of Palæontology.
If this historical sketch had been prepared within a few years of the
death of Cuvier, it would no doubt have held him up as the greatest
of zoologists and comparative anatomists. Nor would it have been hard
to find reasons for such a verdict. His _Règne Animal_ extended and
corrected the zoological system of Linnæus; his comparative anatomy,
and especially his comparative osteology, were far ampler and more
exact than anything that had been attempted before. It would not have
been forgotten, moreover, that he was the practical founder of the new
science of palæontology.
At a later time, say in the sixties and seventies of the nineteenth
century, when the Origin of Species controversy was in full blast,
any estimate of Cuvier by an evolutionist would have been much less
laudatory. Cuvier had actively opposed that form of evolution which had
been brought forward in his day, and with such power as to close the
discussion for a time. The assailants of the Origin of Species found
his refutation of unity of type and progressive development adaptable
to the new situation, and the reasoning which had pulverised Geoffrey
St. Hilaire was brought out again in order to pulverise Darwin. Then
the supporters of Darwin found it necessary to show that Cuvier was
by no means infallible. This they were able to do without introducing
matter foreign to the main question, for Cuvier's exposition of fixity
of species, of the principles of classification and of the process of
extinction, were entirely opposed to the beliefs not only of Darwin,
but of Lyell and the whole school which stood out for historical
continuity, treated history of every kind as a process of development,
extended almost without limit the duration of life on the earth, and
enforced the obvious but neglected truth that results of any magnitude
whatever may proceed from small causes operating through a sufficient
length of time.
Darwin's main contentions are now accepted by the scientific world, and
Cuvier's hostility to particular forms of evolution has become a mere
historical episode of no lasting importance. Angry disputes concerning
the weight of his authority are at an end; he is not to be blamed
because thirty years after his death he was set up as judge of a cause
which he had not heard. We are now ready to make fair allowance for
the time in which his lot was cast—an age when geology, embryology,
palæontology, and distribution were mere infants, some of them hardly
yet born. We can also admit without reserve the incompetence of certain
of Cuvier's antagonists, and justify the severity with which he treated
unity of type as stated and defended by Geoffroy St. Hilaire. Now
that the dust of controversy has settled, we are chiefly concerned to
inquire: What of all Cuvier's work has proved to be really permanent?
His zoology and his comparative anatomy have had to be completely
re-cast, partly because of the new light thrown on them by embryology
and the doctrine of descent with modification. His studies of extinct
vertebrates, however, called into existence a new science, the science
of Palæontology,[33] and it is mainly this which gives him a lasting
and honoured place in the history of biology.
At the end of the eighteenth century it had been rather grudgingly
admitted that some few animals were actually extinct. Buffon was able
to quote as indubitable examples the mammoth and the mastodon. Their
occurrence in countries unknown to the ancients, such as Siberia
and North America, disposed of the explanation long clung to by the
learned—viz., that their bones were the remains of elephants which had
been led about by the Roman armies, while their large size and the ease
with which they can be recognised rendered it highly improbable that
they still survived anywhere on the surface of the globe.
It was therefore natural that Cuvier's first study in palæontology
should relate to extinct elephants. He compared and distinguished
several species, showed that they were distinct from the existing
Asiatic and African species, a fact which had escaped the notice of
Pallas, and argued from the well-known case of a Siberian mammoth
preserved in ice and frozen mud with hardly any decomposition that
it must have been overwhelmed by a sudden "revolution of the earth."
Whatever we may think of Cuvier's geology, his comparisons of all known
elephants, recent and fossil, introduced a new standard of exactness
into these inquiries. From this beginning he went on to study all
the extinct vertebrates which he could discover in public or private
collections. By 1821 he had published elaborate and well-illustrated
descriptions of near a hundred extinct animals, an extraordinary output
for one investigator.
The most remarkable of his palæontological discoveries were made at
home, in the lower tertiary rocks which underlie the city of Paris. He
proved that in the valley of the Seine a large population of animals,
all now extinct, had formerly flourished. None of these discoveries
impressed his contemporaries more than the celebrated case of the
fossil opossum. The bones were imbedded in a slab of gypsum, and
were at first imperfectly exposed. The lower jaw, however, exhibited
a peculiarity of marsupial or pouched animals, for its angle had an
inwardly projecting shelf, not found in other quadrupeds. The opossums,
like all marsupial animals, bear on the front of the pelvis two long
bones, which support the pouch. These were as yet concealed, and Cuvier
delayed clearing them until he had summoned friends, some of whom may
have been sceptical about the possibility of reasoning with certainty
from anatomical data. Warning them what to expect, he removed with
a sharp tool the film of stone, and revealed the long and slender
marsupial bones.[34] The ancient existence of marsupials in France was
then a striking and almost incredible fact; increase of knowledge has
not lessened its interest, though it has abated some of the wonder.
The fossil ungulates (hoofed quadrupeds) of the Paris basin taxed
Cuvier's patience and skill to the utmost. In the tiresome work of
piecing together a multitude of imperfect skeletons he set an example
to all future palæontologists. That he drew general conclusions which
we are unable to accept, and failed to draw conclusions which seem
obvious to us, will surprise nobody whose reading has taught him how
unprepared were the biologists of that age to handle great questions
concerning the origin and extinction of races. Cuvier recognised among
the fossils of the Paris quarries the bones of two genera of ungulates
very different from any of recent times. One resembled the rhinoceros,
tapir, and horse in being odd-toed; this he called Palæotherium.
Another had the hind-foot even-toed, like a ruminant, though the
fore-foot, with which he was imperfectly acquainted, showed points of
resemblance to the other group. How cautiously he did his work may be
gathered from the fact that he spent fifteen years upon the collection
of facts before he attempted to restore these extinct forms, though
almost every bone in their bodies had during that time passed through
his hands.
The great interest of these fossil ungulates to the modern biologist is
that they are relatively primitive types of the order. Palæotherium is
not far from the ideal common ancestor of the rhinoceros, tapir, and
horse; Anoplotherium not altogether unlike the ideal common ancestor of
the hippopotamus, the swine, and the ruminants. It has been suspected
that Cuvier was less obstinately devoted to the tenet of fixity of
species than he was willing to admit in public. Whatever his private
leanings may have been, he stood out resolutely for cogent proofs of
transmutation. When it was contended that the Palæothere might have
been the remote ancestor of existing ungulates, he demanded that the
intermediate links should be produced. His demand could not be met till
many years later, though intermediate forms between the Palæothere
and the horse have since been furnished in abundance. Reserve about
far-reaching deductions was surely wise at a time when plausible
speculation was rife, and we ought not to judge Cuvier severely for
having aspired to a rigour unattainable in a natural science, and
certainly not always observed by himself. He hoped to see biology
become as exact as astronomy. The hope may have been chimerical, but
emphasis on this side was not altogether out of place in the generation
of Geoffroy St. Hilaire and Oken.
If the great master who laid the foundations of palæontology could
revisit the scene of his former labours, he would find that many
strange things had happened since the appearance of his _Ossemens
Fossiles_. He would perhaps be stupefied at first to discover how
little is now made of the Revolutions of the Earth, the proofs of
which had seemed to him unimpeachable, while the conjectures about
the development of new races, which in his own day had been almost
negligible, have proved to be anticipatory of fundamental biological
truths. The first shock over, one can imagine the zest with which
he would strive to combine the familiar facts into a body of new
doctrine. The ungulates, recent and fossil, would of course interest
him particularly. He would recognise the gradations of structure which
run through the whole order, branching and crossing in all directions;
gradation in the number of the toes, in the rearing of the body more
and more upon the toe-tips, in the progressive complication of the
teeth. One chain of examples would lead from the shallow, tuberculate
molar of the pig to the molar of the horse or ruminant, deep and
massive, with crescentic enamel-folds; another would illustrate the
gradual development of tusks from ordinary incisors or canines; a
third series would show the steps by which the primitive ungulate
dentition became reduced to the dentition of the elephant, with only
a single pair of incisors, enlarged into tusks several feet long,
with no canines but molars of great weight, complicated by extreme
folding. It would surprise and delight him to compare the almost
insensible steps by which his own Palæothere can be seen to pass into
the modern horse. Then we can imagine how our regenerate Cuvier would
draw nearer and nearer to the common ancestor of the whole group, a
five-toed, plantigrade ungulate, with the full dentition of forty-four
unspecialised teeth, and how readily he would admit that Phenacodus,
both in its structure and its geological horizon, was just the common
ancestor that theory required. The proofs of intermediate stages
between ancient and modern ungulates which he had once called for in
vain, he would now find ready to his hand. It might well seem that the
history of the ungulates, with all its modern expansions, would suffice
to occupy even his unparalleled energy. He would see with delight how
the palæontology which he had been the first to treat as a science
has enlarged the comparative anatomy of which also he was so great
a master. He would cheerfully admit that both yield proofs of that
doctrine of descent with modification which a hundred years ago seemed
to him so questionable.
[Illustration: GEORGES CUVIER.
From an engraved copy of the portrait by Pickersgill.]
Chamisso on the Alternation of Generations in Salpa.
Trembley (see p. 57) had shown that Hydra, though an animal, multiplies
by budding like a plant. He got indications, upon which he did not
altogether rely, that it also propagated by eggs, and ten years later
(1754) this supposition was confirmed by Roesel, who figured the egg,
though he was unable to demonstrate that a young Hydra issues from it;
subsequent inquiry has placed the fact beyond doubt. In 1819 Chamisso
announced that Salpa, a well-known Tunicate which abounds at the
surface of the sea, exhibits a regular alternation of the two modes of
increase, the egg-producing form being succeeded by a budding form,
the budding form by the egg-producing form, and so on indefinitely.
Sars a few years later showed that the common jelly-fish Aurelia also
propagates by eggs and buds alternately. Here the familiar swimming
disks, which are of two sexes, produce eggs from which locomotive larva
issue. The larva at length settles down and takes a Hydra-like form.
It pushes upwards an ascending column, which divides transversely and
forms a pile of slices, each destined to become a free, sexual Aurelia.
The alternation of generations may be regarded as resulting from the
introduction of budding into the early stage of a life-history which
culminates in sexual reproduction, much as if a caterpillar were to
divide repeatedly and form more caterpillars, each of which ultimately
became a moth. The case which has been given as an illustration
actually occurs in nature. A parasitic caterpillar, that of Encyrtus,
divides while still an embryo, so that one egg produces several
moths.[35] Many other cases of alternation have since been found among
animals, and it seems to be the rule among plants.
Alternation of generations may be complicated by association with
transformation, by the omission of stages usual in the class, and by
budding-out from one part instead of from the whole body. In particular
cases the complication becomes so great that biological language breaks
down under it. Such terms as _generation_, _individual_,
_organ_, _larva_, _adult_, cannot always be used
consistently without either being strained or artificially limited.
Baer and the Development of Animals.
The curiosity of the ancient Greeks led them to look for the chick
within the egg, and Aristotle mentions the beating of the heart as a
thing which might be observed in a third-day embryo. After the revival
of science Fabricius of Acquapendente figured the chief stages of
development, from the first visible rudiments to the escape from the
egg-shell. Harvey, the discoverer of the circulation, not only studied
the developing chick, but took advantage of the rare opportunity
of dissecting breeding does from the royal parks. His treatise on
Generation is unfortunately impaired by Aristotelian philosophy, and
some of the theories there set forth gave much trouble to Swammerdam.
The oft-cited maxim "Omne vivum ex ovo" does not occur exactly in this
form in Harvey's writings,[36] nor does it fairly state his own belief.
Those who read his _De Generatione_ will see that his knowledge was
insufficient to justify so wide a generalisation; on this head it is
enough to mention that he was persuaded of the production of insects
without parents from putrefying matter.[37]
Malpighi was the first to apply the microscope to the embryonic chick.
His figures are surprisingly full of interesting detail, and so far
in advance of their age that they long failed to produce their due
effect. On one point Malpighi unconsciously led naturalists astray for
a hundred years or more. On examining a fowl's egg which he supposed to
be unincubated, he discovered within it an early embryo. From this he
concluded that the embryo _pre-exists_ in the egg, like a plant-embryo
in a seed. He mentions one circumstance which makes everything
intelligible. The egg was examined in August, during a time of great
heat, and the Italian summer no doubt started development, like the
hot sand of Aden, in which Chinamen hatch their eggs. Swammerdam too
enforced the same belief in pre-existing germs. From the fact that the
butterfly can be revealed by opening the skin of a full-fed caterpillar
he inferred (quite contrary to the opinion which he expresses
elsewhere) that one animal had formed inside another. This led him to
say that there is no such thing as generation in nature, but merely
the expansion of germs which lie enclosed one within another. By his
theory he explained how Levi could pay tribute to Melchizedek before he
was born, and how the sin of Adam can be laid to the charge of all his
posterity. The belief in the pre-existence of germs was first shaken by
Caspar Wolff (see p. 81), who examined unincubated eggs but found no
germ which could be detected by the histological methods then employed.
Swammerdam's _Biblia Naturæ_ contains useful figures of early and
late tadpoles; in particular, he describes a stage in which the body
is entirely composed of rounded "lumps" or "granules," the _cells_
of modern biology.
Early in the nineteenth century Pander and Baer, both of whom were
pupils of Döllinger, a teacher of extraordinary influence, gave a
new impetus to the study of development. Pander (1817-8) published an
account of the early stages of the chick, illustrated by beautiful
plates by D'Alton. Baer (1828-37) carried the work much further, not
only greatly extending the knowledge of the developing chick, but
discovering the mammalian ovum (1827), and announcing generalisations
which down to 1859 were the most luminous that embryology had ever
furnished; we may call him the founder of comparative embryology.
He shows that development may supply decisive indications of the
zoological position of animals; it teaches, for instance, that insects
are of higher grade than arachnids or crustaceans, and that amphibians
ought not to be united with reptiles. He describes the development
of an animal as a process of differentiation, the general becoming
special, and the homogeneous heterogeneous; differentiation is, he
remarks, the law under which not only animals but solar systems
develop. He maintains that the embryo, though gradually attaining
complexity, makes no transition to a different type—_e.g._, the
vertebrate is never in any stage anything but a vertebrate. All
animals, he believes, are probably at first similar, and take the
form of a hollow sphere (the _gastræa_ of modern embryology). There
are, he says, no new formations in nature; all is conversion. When he
comes to speak of the pharyngeal clefts of mammals and birds, recently
discovered by Rathke, he remarks that their correspondence with the
gill-clefts of fishes is obvious. We wonder what is coming next, but
our curiosity is not gratified by any memorable deduction. Neither
here nor in his miscellanies (_Reden_), published nearly fifty
years later, does he admit that mammals and birds can have descended
from gill-breathing vertebrates. If we are inclined to hint that Baer,
having gone so far, might well have gone a little farther, it is only
fair to recollect that every leader in science is more or less open to
the same reproach.
The Cell Theory.
Any one of the higher animals or plants admits of analysis into
_organs_, each adapted to one or more functions. Bichât (1801) showed
that the body of one of the higher animals is not only a collection
of organs, but also a collection of _tissues_, and the same is true
of the higher plants. Analysis of the organism was carried a step
further when in 1838-9 Schleiden and Schwann announced that all the
higher animals and plants are made up of _cells_, which were at first
supposed to consist in every case of a cell-wall, fluid contents, and
a nucleus.[38] It was soon discovered that the cell-wall is as often
absent as present, and that the cell-contents are not simply fluid; the
nucleus is still believed to be universal. Schwann proved that nails,
feathers, and tooth-enamel, though not obviously cellular, consist of
nothing but cells, and it was afterwards shown that bone, cartilage,
fatty tissue, and fibrous tissue arise by the activity of cells which
disappear from view in the abundance of their formed products. The
individual cells of a complex organism are usually themselves alive;
sometimes, as in ciliated epithelium, they give indications of life
longafter they have been separated from the body. The preponderating
importance of the transparent jelly or protoplasm became clear when
it was recognised that this alone is invariably present, and that
this alone responds to stimuli. The nucleus is believed to be only a
specialised part of the cell-protoplasm.
The cell-theory, like nearly every theory, was neither altogether new
nor in its first form altogether complete. Before 1838 cell-division,
as we should now call it, had been indistinctly seen to be the process
by which the body of one of the higher animals is built up. Leeuwenhoek
and Swammerdam had found a wholly cellular stage in frog-embryos (see
p. 103), while Prévost and Dumas in 1824 had in effect discovered that
the cells of which such embryos consist result from repeated division
of an egg; Mohl in 1835 observed the actual division. Even Schwann,
however, was not acquainted with the important fact that every cell
arises by the division of a pre-existing cell.
Swarm-spores of algæ showed that protoplasm, when unenclosed in a
cell-wall, can move about, direct its course, and change its shape.
Knowledge of this fact did more than rectify the definition of the
cell; it effaced one distinction between plants and animals, and gave a
hint of the resemblance of primitive cells to such simple organisms as
Amœba.
Martin Barry in 1843 announced that certain Protozoa (that name was
not yet in use) are simple cells. He pointed out that they possess
nuclei, like those of tissue-cells, and compared their increase by
fission with the cleavage of the egg. Single cells were thus shown to
be not only capable of locomotion, which was already known, but able
to provide for their own support. The Protozoa and Protophyta (_i.e._,
the simplest animals and plants, which are not always to be clearly
separated) are now known to be autonomous cells, increasing by fission,
and often forming colonies. Conjugation (fusion of similar individuals)
often precedes fission, and when it was proved (1861-5) that ova and
spermatozoa are true cells, it was seen that fertilisation, as we know
it in the higher animals, is only a special form of the conjugation
observed among the Protozoa. To the Protozoa it is now possible to
trace, without any startling break of continuity, all the multicellular
organisms, their tissues, the growth of those tissues by repeated
fission, their eggs, and the process of fertilisation which precedes
cleavage. The old Greek riddle, "Which came first, the fowl or the
egg?" may now receive the answer: "Neither; their common starting-point
is to be found in the Protozoa, which, even when adult, represent the
primitive unicellular condition, to which all the higher animals revert
once in every generation."
It is not without reason that biologists dwell on the unifying
influence of the cell-theory, which has become a chief support of that
still wider unifying influence, the _Origin of Species by Natural
Selection_. When it was discovered that all living things, whether
plants or animals, consist of nucleated cells which increase by
fission, and that in all of them cell-fission is started anew from time
to time by a cell-fusion, it was strongly suggested that resemblances
so striking and so universal can only proceed from a common descent.
During the last half-century the study of cells has led to a great
increase of knowledge respecting all bodily functions, whether in
health or disease. We now look to it as perhaps the most hopeful source
of new light upon the important question of hereditary transmission.
The Scientific Investigation of the Higher Cryptogams.
We now resume the history of a study which down to the end of the
eighteenth century had yielded only meagre and uncertain results (see
above, pp. 85-88). At the date in question it had been ascertained
that the spores (then called "seeds") of ferns, and probably of other
cryptogams, are capable of propagating the species, but no one knew
precisely what part the spore played in the life-history, or could
explain the true difference between a cryptogam and a flowering plant.
The great improvements in the construction of the compound microscope
which were effected between 1812 and 1830 rendered it possible to
elucidate much more thoroughly the structure and development of the
chief groups of cryptogams. The sexual reproduction of algæ was
explored; moving filaments (spermatozoids) were seen to enter the
chambers in which embryos afterwards formed; the conjugation of similar
cells was observed in algæ and fungi, and recognised as a simple mode
of sexual reproduction. The resemblance of the spermatozoids of mosses
and ferns to animal spermatozoa was noted, and their participation in
the process of fertilisation was more and more closely followed until
at length Hofmeister in 1851 saw them fuse with the egg-cell of a fern.
Suminski, whose full name, Lesczyc-Suminski, is unpronounceable by
Englishmen, had discovered (in 1848) that the prothallus of a fern,
which is the product of the germinated spore and had been hitherto
taken for the cotyledon, bears two kinds of reproductive organs, one
of which liberates spermatozoids, while an egg-cell is developed
within the other. He did not correctly describe all the details, but
he showed where the essential reproductive organs form, and where
fertilisation is effected. The masterly researches of Hofmeister
(1849-57) fused what had been a number of partial discoveries into a
connected and luminous doctrine. He proved that the prothallus is one
of two generations in the life-history; that it begins with a spore and
ends with a fertilised egg-cell; that in the higher cryptogams there
is a regular alternation of generations; that the prothallus of the
fern answers to the leafy moss, while the leafy fern is the equivalent
of the moss-capsule; that the egg-cell is the same structure in both
cryptogams and flowering plants; that the pollen-tube and the seed are
found to-day only in flowering plants; that the gymnosperms make a
transition from the higher cryptogams to the angiosperms; that unity
of plan pervades the whole series of mosses, ferns, fern-like plants,
gymnosperms, and angiosperms. Before Darwin's _Origin of Species_ had
appeared Hofmeister presented to evolutionists a clear example of a
descent in which every principal term is well authenticated, while the
extremes are far apart.
The Enrichment of English Gardens.
If some unreasonably patriotic Englishman should be seized with the
whim of keeping none but truly British plants in his garden, he
might enjoy the shade of the fir, yew, oak, ash, wych-elm, beech,
aspen-poplar, hazel, rowan-tree, and the small willows, but he would
have to forego the common elm, the larger poplars and willows, the
larches, spruces, and cypresses, the rhododendrons, and all the shrubs
popularly called laurels. Of fruits he might have the crab-apple, sloe,
wild cherry, gooseberry, currants (black and red), the raspberry,
strawberry, and blackberry, but none of the improved apples, pears,
or plums, and no quinces, peaches, or apricots. His vegetable garden
might yield cabbages, turnips, carrots, and celery (all deficient in
size, flavour, and variety), but no cauliflowers, Brussels sprouts,
parsley, lettuces, peas, beans, leeks, onions, or spinach. The
handsomest of his flowers would be dog-roses, mallows, and primroses.
Before Europe was sufficiently enlightened to care about exact records
valuable foreign plants had already been introduced. Vines, apples,
pears, cherries, and plums, besides improved vegetables, such as the
cauliflower, bean, garden-pea, and cucumber, had been brought from
temperate Asia or Egypt. Wheat and barley, neither of them native
to Europe, had to some extent replaced rye and oats, which may have
existed naturally in those European countries which border on Asia.
Britain, while yet a Roman province, shared in these benefits, and
it is believed that the common elm, besides certain fruit-trees and
pot-herbs, have been continuously grown in our island through all
the troubled ages which separate us from the Romano-British times.
Leek, garlic, and onion are ancient acquisitions. To our Old-English
forefathers garlic was the _spear-leek_, distinguished by its long,
narrow leaf from the broad-leaved common leek, just as a garfish was
distinguished from other fishes by its long body and pointed head;
onion was the _enne-_ or _ynne-leek_ (onion-leek); the most
important of the three was probably that which retained the root-word
without prefix—the leek proper.
During many centuries, when the rights of small proprietors were
little respected and knowledge was scanty, the religious houses were
distinguished by the diligence with which they tended their gardens.
Flowers, fruits, and simples were cultivated, and plants were now
and then imported from foreign monasteries. The English names of the
plants, which are often adaptations of Latin words, still testify to
the care of gardeners who were in the habit of using Latin.
Much improvement was not to be expected so long as England suffered
from frequent and desolating wars within her own borders. When these
at last subsided, great English gardens, such as those of Nonsuch,
Hatfield, Theobalds, and Hampton Court, began to parade their beauty;
strange trees, shrubs, and flowers were brought from the continent,
and as early as Queen Elizabeth's time our shrubberies and walks were
admired by spectators familiar with the best that Italy and France
could show. The new horticulture was, however, long an exotic among
us, and John Evelyn, whose _Sylva_ appeared in 1664, was "the
first to teach gardening to speak proper English."
In the latter part of the sixteenth century the following new plants
among others were brought from central or southern Europe: The poppy
and star anemones, the hepatica, the common garden larkspur, the winter
aconite, the sweet-William, the laburnum, Rosa centifolia (of eastern
origin, the parent of countless varieties and hybrids), the myrtle, the
lavender, the cyclamen, the auricula, Iris germanica, and many other
Irids, the oriental hyacinth, several species of Narcissus, the white
and Martagon lilies, and the absurdly named dog's-tooth-violet (really
a lily). The botanist Clusius introduced the jonquil and the Tazetta
narcissus from Spain to the Low Countries. The Judas-tree (_i.e._,
tree of Judæa) was brought from the Mediterranean, where the hollows of
the hills are filled in April with its pale-purple blooms. The white
jasmine was imported from Asia, and the castor-oil plant from Africa.
The great accessions of geographical knowledge made during the
fifteenth and sixteenth centuries were slow to affect horticulture.
Ships were then few and small, and the passage from Hispaniola or
Calicut to Cadiz or Lisbon occupied weeks or even months. Moreover,
the conquests of Spain and Portugal (Goa, the Moluccas, Brazil,
the West Indies, Peru, and Mexico) lay mostly within the tropics,
and could furnish hardly any plants capable of enduring a European
winter. Special pains were, however, taken to bring over some valuable
food-plants which were thought likely to thrive in Europe. Before
any European landed in America the potato had been cultivated by the
Indians of Peru, a country which, though lying almost under the line,
rises into cool mountain-districts. Potato-tubers were soon introduced
to Spain and Italy, and a little later to other parts of Europe;
Raleigh's planting of potatoes on his estate near Cork came a few
years later. The edible tomato, which is distinguished from the wild
form by its enlarged fruits, was apparently cultivated in Peru before
the first landing of the Spaniards. The unusually high proportion of
edible plants among the first importations from America and other
distant countries is worthy of remark. Early explorers eagerly sought
for valuable food-plants, but the number of such as could be cultivated
alive in Europe was very limited, and since the sixteenth century the
attention of collectors has been fixed upon ornamental species simply
because of the dearth of others.
European flower-gardens were enriched during the sixteenth century
by the following American species: the so-called French and African
marigolds (both from Mexico), sunflowers, the arbor-vitæ (Thuja
occidentalis), Yucca gloriosa, and the Agave, misnamed the American
Aloe.
About the same time the horse-chestnut, lilac, and syringa, or
mock-orange, were first brought to central and western Europe, and
with them the tulip, richest and most varied of flowering bulbs. All
these reached Vienna from Constantinople, but how and when they were
brought to Constantinople, or what were their native countries, are
still doubtful questions. The horse-chestnut is believed to be a native
of Greece, where it is said to grow wild among the mountains; probably
it extends into temperate Asia as well. It is said to have reached
Constantinople in 1557. Longstanding tradition derives the lilac
from Persia, but botanists say that it is also indigenous to parts
of south-eastern Europe. The garden-tulip is believed to be native
to temperate Asia and also to Thrace; it is, of course specifically
distinct from the wild tulip of northern Europe.
Chief among the travellers to whom we owe the acquisition of these
favourite plants was Augier Ghislen de Busbecq, a Fleming, who was
twice sent by the emperor as ambassador to the sultan. Busbecq was
a keen observer and collector, and during his long and toilsome
journeys was ever eager to pick up curiosities or to note new facts.
Quackelbeen, a physician in Busbecq's suite, is named as another
helper. The botanists Mattioli and Clusius, who presided in succession
over the imperial gardens of Vienna, and Gesner of Zurich, described
the plants; it is from them that we draw such imperfect knowledge as
we possess of the way in which they were brought to central Europe.
Clusius relates that Busbecq in 1575 received a parcel of tulip-seed
from Constantinople, and being obliged to journey into France, left
it with Clusius to be germinated. The tulips which came up were of
various colours, an indication of long cultivation. The Turks, like the
Persians, took great delight in gardens.
As North America became permanently occupied by the English, facilities
for the transport of live plants to Europe steadily increased. Ships
began to sail frequently to and fro, for the crossing of the Atlantic
was but a small affair in comparison with the voyage round the Cape
of Good Hope. Educated men here and there practised the learned
professions in the American plantations, and among them a sprinkling of
naturalists was found. Hothouses, the amusement of wealthy amateurs in
Germany, France, and Holland, made it possible to protect the plants
of mild climates from the winter cold of northern Europe. By the end
of the seventeenth century our gardens had acquired many beautiful and
curious American plants, besides a few from the East Indies, and not
long afterwards the gains became so frequent that the botanists of
Europe found it hard to name the new species as fast as they came in.
Lovers of horticulture will tolerate a little further information
concerning the early use of hothouses. As soon as glass began to
be employed in domestic architecture, the construction of warmed
and glazed chambers, in which plants could be grown, was attempted.
Writers of the first century A.D. mention them, and Seneca
explains how the temperature might be kept up by hot water. This and
other refinements of the Roman Empire passed into oblivion during the
long decline of civilisation, but revived with the revival of the
arts. In the sixteenth century William IV., Landgraf of Hesse, who is
remembered, among other things, as a patron of the botanist Clusius,
built himself a green-house, which could be taken down and put
together again. A still more famous orangerie was that of Heidelberg,
which served as an example to the kings and nobles of Europe.[39] Henri
IV. built one at the Tuileries, and long afterwards Louis XIV. had one
at Versailles. Madame de Sévigné describes the orangerie of Clagny
as a palace of Armida, and the most enchanting novelty in the world.
The pine-apple was brought over from Barbadoes in the seventeenth
century, and Evelyn speaks of having tasted the first pine-apple grown
in England at the table of Charles the Second. For two hundred years
the hothouse yielded no greater dainty, but rapid transit has now
made pine-apples so cheap that it is no longer worth while to raise
them in England. Fagon, who was during many years first physician to
Louis XIV., was a considerable botanist. He was born and died at the
Jardin des Plantes, and here, on his retirement from practice, he built
hothouses; it would be interesting to know what he grew in them.
In the first half of the seventeenth century the younger Tradescant,
who, like his father before him, was gardener to our Charles I.,
brought over from America the spider-wort, named Tradescantia after
him,[40] the false acacia and the tulip-tree. The magnolias, or some of
them, the Virginian creeper, and the scarlet Lobelia cardinalis were
among the gifts received from North America about the same time. The
dwarf Lobelia (L. Erinus) was not brought over from the Cape of Good
Hope till 1752, and Lobelia splendens and fulgens (both from Mexico)
not till the nineteenth century. One of the passion-flowers, which are
all American, came over about this time; but Passiflora cærulea, the
favourite ornament of the greenhouse, was only imported from Brazil in
1699. The evening primrose, the "convolvulus major and minor" (Ipomæa
purpurea and Convolvulus tricolor), were other acquisitions from North
America.
From the second half of the seventeenth century dates the introduction
of the garden nasturtium (Tropæolum majus) from Peru; T. minus from
Mexico had been brought over nearly a hundred years earlier. The
sensitive plants and the pine-apple now became frequent objects in
English greenhouses. John Evelyn and Bishop Compton were eminent
patrons of English horticulture during this age.
The first half of the eighteenth century brought us the Aubretia and
the sweet pea from southern Europe, the first Pelargoniums (scarlet
geraniums) from the Cape, the camellia and Kerria japonica from the
far east. The West Indian heliotrope was introduced in 1713; the
better-known Peruvian species not till 1757. Phloxes began to be
imported from North America. Two or three foreign orchids were already
known, and the number now began to increase; but it was not till the
nineteenth century that they came over in crowds. Our list gives no
notion whatever of the number of new species added now and subsequently.
Of the accessions made during the latter half of the eighteenth century
we must at least mention the mignonette from North Africa, white arabis
from the Caucasus, the common rhododendron from Asia Minor, Rosa
indica and Hydrangea hortensis from China, South African gladioli,
which now begin to be numerous, and chrysanthemums from China and
Japan. The first calceolarias were brought from great heights on the
Andes, the first begonias from Jamaica, and the first fuchsia from
Chili.
We can make only one remark about the multitudinous accessions of
the nineteenth century. It is surprising to note how recently many
established favourites have been brought to the knowledge of English
gardeners. Anemone japonica (Japan) and Jasminum nudiflorum (China)
date from 1844, while the Freesias (Cape Colony) are as recent as
1875. The dahlia, after two unsuccessful attempts, was established
here as recently as 1815; Nemophila insignis came over from North
America in 1822; the common musk and the monkey-plant a few years
later; the chionodoxas (Crete and Asia Minor) in 1877. The first of the
foliage-begonias (Begonia rex from Assam) dates only from 1858, and the
first of the tuberous species from 1865.
Importation of foreign species has not been the only method by which
English gardens have been enriched. New varieties and hybrids have
been produced in bewildering numbers by the gardeners of Europe, and
many of these far surpass in beauty the wild originals. Botanists
and nurserymen could relate in great detail the steps by which our
favourite roses, calceolarias, begonias, and cinerarias have been
developed from a few natural stocks, sometimes of uninviting appearance.
Horticulture has repaid the debt which it owed to the explorations
of botanists by furnishing countless observations and experiments
bearing upon inheritance. When these have been properly co-ordinated,
they will yield precious knowledge, not only to botanists but to all
students of biology.
Humboldt as a Traveller and a Biologist.
The career of Alexander von Humboldt (b. 1769, d. 1859), nearly
coinciding with the period on which we are now engaged, was devoted
to a gigantic task—nothing less than the scientific exploration of
the globe. His great natural powers were first cultivated by wide and
thorough training, not only in astronomy, botany, geology, mineralogy,
and mining, which had an obvious bearing on his future enterprise,
but also in anatomy, physiology, commerce, finance, diplomacy,
and languages. Thus equipped, he sailed in 1799 with the botanist
Bonpland to South America, and spent the next five years in exploring
the Orinoco and Amazon, the Andes, Cuba, and Mexico. The expedition
marks an epoch in scientific geography. It is enough to mention the
collection of data for the more accurate mapping of little-known
countries, the exploration of the river-systems of equatorial America
and the discovery of a water-connection between the Orinoco and the
Amazon, the ascent of lofty mountains, the study of volcanoes, the
description of remarkable animals such as the howler-monkey and
the gymnotus (electric eel), and of remarkable plants, such as the
bull's-horn acacia, whose enlarged and hollow spines are occupied
by ants.[41] After his return to Europe Humboldt published many
important treatises on terrestrial magnetism, geology, meteorology,
and plant-distribution. His new graphical method of isothermal lines
did much for the study of climate in all its bearings. His _Personal
Narrative_ not only disseminated much interesting information, but
inspired a new generation of explorers. Darwin agreed with Hooker that
Humboldt was the greatest of scientific travellers.
In 1829 Humboldt traversed the Russian Empire from west to east,
but the time allowed (half a year) was altogether insufficient for
the examination of so vast a territory; a few notable results were,
nevertheless, secured.
After some fifteen or twenty years spent in European society, the
inspiration drawn from long and arduous journeys in South America began
to fail. The conversation of the _salons_, the troublesome flattery
of the King of Prussia, and the propensity to write copiously,
stimulated, of course, by the eagerness of the public to buy whatever so
eminent an investigator chose to put forth, sterilised the last half of
a career which had opened with such magnificent promise.
The best of Humboldt's work became absorbed long ago into the confused
mass of general knowledge. This is the common fate (not by any means an
unhappy one) of those who refuse to concentrate upon a single study.
Among biologists he is chiefly remembered by his numerous discussions
of plant-distribution, which are now considered less remarkable for
what they contain than for what they leave out. While his travels were
fresh in his mind, Humboldt was impressed by facts of distribution
which could not be explained by present physical conditions,[42] but
the influence of climate as the more intelligible factor gradually
assumed larger and larger proportions in his mind. The writers of
text-books, founding their teaching upon Humboldt, often overlooked
altogether qualifications which he had shown to be necessary. When
Darwin and Wallace pointed out how immensely important is the bearing
upon present distribution, not only of the physical history of the
great continents, but also of their biological history, and in
particular of the interminable conflicts of races of which they have
been the scene, naturalists began to perceive how inadequate are
horizontal and vertical isothermal zones to explain all the striking
facts of distribution, whether of plants or animals (see _infra_ p 129).
Premonitions of Biological Evolution.
The eighteenth century had done much to impress the minds of men with
an orderly development in sun and planets (Kant and Laplace), in
the institutions of human societies (Montesquieu), and in the moral
aspirations of mankind (Lessing). Many bold attempts had been made
to trace a like orderly development in the physical life of plants
and animals (Buffon, Erasmus Darwin, etc.), but neither was the proof
cogent nor the process intelligible. Cautious people therefore, and
those whose prepossessions inclined them to adopt a very different
origin for terrestrial life, held during all this time a position of
some strength against speculative philosophers who tried to explain
the variety and perfection of living nature by unconscious and
unintelligent factors.
About the year 1840 the doctrine of the fixity of species seemed to be
victorious. Cuvier's knowledge and skilful advocacy had a few years
before over-powered Geoffroy St. Hilaire's conception of a common
plan of structure pervading the whole animal kingdom, and the new
_Philosophie Anatomique_ was laid on the shelf, side by side with
the _Philosophie Zoologique_ of Lamarck, the _Zoonomia_ of Erasmus
Darwin, the _Théorie de la Terre_ of Buffon, and the _Protogæa_
of Leibnitz. Yet even then a spectator who was fully informed and at the
same time gifted with uncommon foresight might have satisfied himself
that the victory of evolution had become inevitable.
Cuvier's memorable descriptions of the extinct vertebrates of the
Paris basin had founded the new science of Palæontology, and though
neither he nor anyone else was aware of the fact, had made it possible
to trace, very imperfectly no doubt, the descent of a few modern
ungulates. Lyell's _Principles of Geology_ (1830-3) had shaken the
belief in catastrophes repeatedly breaking the succession of life on
the earth. It was rapidly becoming impossible to maintain that the
account of creation given in the book of Genesis was even approximately
accurate. In the year 1828 Baer had almost made up his mind that the
facts of development pointed to a common plan of structure, perhaps
to a common origin, for each of the great types of animal life.[43]
Darwin's _Journal_ had appeared in 1839, and though the explanations
which it offered were not inconsistent with prevalent opinion,
evolutionary suggestions were introduced into the second edition of
1845. Lyell at least was already aware that the voyage of the _Beagle_
had impelled Darwin to examine afresh the accepted philosophy of
creation. Between 1840 and 1850 faint signs of coming change struck
orthodox reasoners with misgiving and gave increased confidence to
free-thinkers. A few German botanists and zoologists declared against
the immutability of species. The _Vestiges of the Natural History of
Creation_, which might be called a premature explosion, dates from
1844. Hofmeister (see supra, p. 109) put forth a detailed comparison
of the flowering plants with the higher cryptogams, which strongly
suggested a theory of descent with modification, and is unintelligible
on any other basis. He indicated no such interpretation himself, being
content to establish the new homologies; but the _Origin of Species_,
as soon as it appeared, commanded his entire sympathy.
Among those who rejected fixity of species and special creation before
1859 none was so clear or so outspoken as Herbert Spencer, who thought
out for himself an evolutionary philosophy which was not shaken by
Darwin. It is impossible to discuss in this place the question whether
or not it was shaken by Weismann.
Agassiz's _Essay on Classification_, which was published in October,
1857, was the last manifesto issued before the _Origin of Species_
by the party which stood out for fixity of species, the last polemic
which made De Maillet, Lamarck, and the _Vestiges_ its targets. It
is an eloquent but inconsiderate defence of an extreme position.
According to Agassiz every branch, class, order, family, genus, and
species represents a distinct creative thought; every mark of affinity,
every appearance of adaptation to surroundings, has been expressly
designed. Extinction and replacement of species are due to the direct
intervention of the Creator; pterodactyls are prophetic types of
birds, and indicate that divine wisdom had foreseen the possibility of
an advance in the organisation of animals which was not immediately
practicable; the mallard and scaup duck occur on both sides of the
Atlantic because they were simultaneously but separately created in
Europe and North America; the teeth of the whale, which never cut the
gum, are the result of obedience to a certain uniformity of fundamental
structure. Explanations like these removed no difficulties and
suggested no inquiries. In the hot debates which ensued the _Essay on
Classification_ was rarely mentioned.
[32] _Cross and Self-Fertilisation of Plants_, chap. xi.
Darwin could exhaust the inquiry. "The veil of secrecy," he goes on,
"is as yet far from lifted."
[33] Cuvier did not himself use the word _palæontology_, which first
came in about 1830. In the same way Buffon writes on the history of
animals, not on _zoology_, and on the theory of the earth, not on
_geology_.
[34] This anecdote has also been related in a rather different form.
[35] The same process of "embryonic fission" occurs in other animals
also, one of which is a mammal (Praopus).
[36] Linnæus (Fund. Bot. § 134, and Sponsalia Plantarum) gives it as
above; Harvey has "Ex ovo omnia"; "ovum esse primordium commune omnibus
animalibus," etc.
[37] Harvey need not have gone outside the writings of Aristotle to
get the substance of his generalisation. He would have found there
that the chief task of both plants and animals is propagation, either
by seeds, or eggs, which Aristotle believed to be equivalent to seeds
(_Hist. anim._, VIII., i.; _De anim. gen._, I., iv.; I., xxiii.).
Aristotle excepted the "imperfect animals," such as insects, and the
seedless plants, concerning both of which his knowledge was misty and
inaccurate; there is no indication that Harvey was better informed.
[38] Hooke figured a thin section of dry cork in his _Micrographia_
(1665), remarking that it was divided into "little boxes or cells."
The word _cell_ was suggested by the resemblance of the tissue to a
honeycomb; since 1838 it has been thoughtlessly extended from the
skeleton to the particle of living matter enclosed within it. Robert
Brown (1831) showed that a nucleus is usual in plant-cells; it had been
figured by Fontana and others long before. Down to 1838 no results of
biological interest followed from the discovery.
[39] Parkinson (1629) speaks of a stove or hothouse, "such as are used
in Germany."
[40] The graceful practice of naming genera of plants after benefactors
to botany or horticulture was introduced by Father Plumier (1646-1704),
who gave the names of L'Obel and Fuchs to the Lobelia and Fuchsia, and
whose own name is appropriately borne by the frangipane (Plumeria).
[41] See the account of Cartagena in the _Personal Narrative_.
[42] See particularly his _Essai sur la géographie des plantes_ (1805).
[43] Baer's expressions are so guarded that his real opinions in 1828
can only be surmised. He never accepted a consistent theory of organic
evolution.
PERIOD V.
(1859 AND LATER)
Period V.
We do not attempt to characterise our last period, nor to describe its
biological achievement. It seems better to devote the whole of our
scanty space to the scientific careers of Darwin and Pasteur, in which
so much past effort culminated, and from which so much progress was to
spring.
Darwin on the Origin of Species.
Setting aside as superfluous and we might say impossible, under our
conditions of space, all attempt to restate the evidence on which
Darwin based his great argument, we shall here try to show that the
_Origin of Species_ shed a new light upon many biological facts,
combined many partial truths into one consistent theory, and gave a
great stimulus to further inquiry.
1. _Classification and Affinity._—The sixteenth-century herbalists
and still earlier writers (see p. 17) recognised a property of
_affinity_, by which plants were associated in natural groups. Bock (
1546) tried to bring together all plants which are related (verwandt)
to one another, but similarity of any kind was with him a proof of
affinity; it did not shock him to place the dead nettles next to the
stinging nettles. L'Obel gave names to several families of flowering
plants which are still admitted as natural. Ray spoke of the _affinity_
(cognatio) between plants, and his affinity was a thing not to be
violated for the sake of practical convenience or logical rules, but he
was unable to explain what he meant by it. Linnæus tried to illustrate
affinity between plants by contiguous provinces on a map, a better
metaphor than the linear scale, for the scale can only express affinity
on two sides, while the map can express affinity on many. His practical
experience of classification taught him a truth, shocking at first sight
to the logician[44]—viz., that the characters which serve for the
definition of one genus may be useless for the definition of the next,
and he laid it down that the characters do not make the genus, but the
genus the characters. After Linnæus we find for a long time no advance
in the philosophy of natural classification. Cuvier (1816) is even
retrograde, for he sets aside the maxims of Linnæus, maintains that
adaptive characters (characters closely related to the conditions of
life) are relatively constant, and that large groups should be defined
by characters drawn from organs of great physiological importance.
These decisions of his are repudiated by later naturalists.
The key to the affinity puzzle which had so long baffled thinking
naturalists was at last supplied by Darwin, who explained that "the
natural system is founded on descent with modification; that the
characters which naturalists consider as showing true affinity between
any two or more species, are those which have been inherited from
a common parent, all true classification being genealogical; that
community of descent is the hidden bond which naturalists have been
unconsciously seeking, and not some unknown plan of creation, or the
enunciation of general propositions, and the mere putting together and
separating objects more or less alike."[45]
Natural groups, large or small, result from the long-continued
operation of divergence, the survival of some, and the extinction of
others; they are to be respected as facts; they are not created by
definitions, which only serve to indicate and remind; any character,
however trifling, will suffice, if only it is constant and distinctive.
The conflict between natural classification and logic is apparent
only. Logicians say that in classifying books, for instance, you may
take any property you please, subject, size, etc., as the basis of
your arrangement, but having made your choice, you must adhere to it
for all divisions of the same rank. Naturalists seem to say something
different, for they are agreed that what they call "single-character
classifications," in which one property is adhered to throughout, are
unnatural. The fact is that a natural classification always rests upon
one and the same property—viz. _affinity_, _i.e._ relative
nearness of descent from some common ancestor. Every natural
classification, like every logical classification, proceeds upon a
single basis, and the failure of the single-character classifications
is due to their displacing affinity by some definition.
The effect of the _Origin of Species_ upon zoological and botanical
systems has been revolutionary. Furnished with a new and intelligible
meaning of the word natural, and with new criteria of naturalness,
systematists have during the last fifty years worked hard to
create classifications which admit of being thrown into the form
of genealogical trees. Wide gaps in the geological history of life
render the task difficult beyond expression, but much has already
been accomplished. Newly discovered forms (especially the fossil
Archæopteryx and the Cycadofilices) and more fully investigated forms,
far too numerous to be specified, have established links between groups
which formerly seemed to be wholly independent. Unnatural assemblages
based on pre-determined characters (Radiates, Entozoa, Birds of prey,
etc.) have been replaced by groups which are at least possible on
evolutionary principles. Almost every working naturalist will admit
that the progress of zoological and botanical system during the last
two generations has done much to fortify the Darwinian position.
2. _Embryology._—Baer in 1828 was possessed of all the embryological
facts which Darwin used in support of his theory of evolution; in
particular, he was well acquainted with the most striking fact of
all—viz., the presence in embryo mammals and birds of a series of
paired clefts along the sides of the neck, between which run vessels
arranged as in gill-breathing vertebrates. The vessels had been figured
by Malpighi; the clefts had been discovered by Rathke, who had no
hesitation in calling them _gill-clefts_ and the vessels
_gill-arches_. Nor had Baer, who nevertheless to the end of his long
life refused to accept the one explanation which gives meaning to the
facts—viz., that remote progenitors of mammals and birds breathed by
gills. Few embryologists have since felt such a scruple. The adaptation
to gill-breathing is obvious; is gill-breathing _now_ practised by any
mammal or bird? Certainly not. Is it destined to be practised by their
descendants at some _future_ time? To say nothing of the danger of
putting forth any such prophecy, it involves all the consequences of
descent with modification. The opponent of evolution may as well admit
at once that the gill-breathing was practised in time _past_. As an
example of the same kind taken from plants, we may quote the trifoliate
leaves of the furze-seedling, which, though absent from the full-grown
furze, are frequent in the family (Leguminosæ) to which it belongs.
The general similarity of vertebrate embryos, of insect-embryos and of
dicotyledonous seedlings, is also worthy of note. We may suppose that
early embryos, being largely or wholly dependent on food supplied by
the parent, and perhaps protected by the parent as well, escape the
pressure of the struggle for existence, and are often not urgently
impelled to produce adaptations of their own. In these circumstances it
is intelligible that features inherited from remote ancestors should
persist. If, however, early independence is demanded by the conditions
of life, the embryo may develop temporary adaptations, wanting in the
parent and in embryos of allied groups. Larval adaptation is as much a
part of the economy of nature as the retention of ancestral structures
which have been lost by the adult.
3. _Morphology._—Let us next consider the light which the Origin of
Species throws upon homologous parts. No example will serve our purpose
better than the very familiar one of the fore-limbs of different
vertebrates, the arm and hand of man, the wing of the bat, the wing of
the bird, the pectoral fin of the fish, and the paddle of the whale.
These limbs, adapted for actions so diverse as grasping, running,
flying, and swimming, nevertheless exhibit a common plan, evident at a
glance, except in the pectoral fin of the fish. But why a common plan?
Of what advantage is it to an animal that its wing, paddle, or hand
should reproduce the general plan of a fore-foot? Why should the digits
of the land vertebrates never exceed five? Why should the thumb never
have more than two free joints? It would be hard to find a satisfactory
answer to these questions in any book earlier than the _Origin of
Species_; no student of the _Origin of Species_ finds any
difficulty in answering them all. The common plan has been transmitted
from type to type by inheritance, and its features are derived from an
unknown common ancestor.
The new conception, that structures inherited from remote ancestors
may be incessantly modified by the conditions of life and by mutual
competition, is the key to the chief problems of morphology. No limited
collection of examples can substantiate so wide a proposition as
this. Those who have made themselves familiar with old text-books of
comparative anatomy will recollect how dry, or else how inconclusive,
was pre-evolutionary morphology, how vague were the references to some
ideal archetype, or to climate, or to the ancient conditions of the
earth's surface; how often exclamations of admiration for the marvels
of nature or Providence were substituted for clear explanations.
Cuvier, it is true, was both precise and reasonable; but how little he
was in a position to explain! His "empirical" comparative anatomy could
throw no direct light upon origins or transformations; his "rational"
comparative anatomy was practicable only in a few easy cases.
4. _Geographical Distribution._—The facts of distribution were
handled in the _Origin of Species_ with great originality. It was
shown that they support, and indeed require, some doctrine of organic
evolution. The succession in the same area of the same types—armadillos
succeeding armadillos in South America, marsupials succeeding
marsupials in Australia—was enough of itself to render independent
creation highly improbable. This was not all. Darwin's mind being
charged with facts and reasonings, the accumulations of many years of
travel and meditation, he sketched in rapid outline conclusions which
have given a new form to the distribution question. The subject had
hitherto been treated by collecting masses of facts and interpreting
them by recent physical geography; Darwin showed that the _history_
of the continents and islands may be far more influential than soil,
elevation, or climate.
The scientific discussion of the facts of distribution is as old as the
sixteenth century, when L'Obel pointed out that the mountain plants of
warm countries descend to low levels in the north. Linnæus remarked
that fresh-water plants and alpine plants are often cosmopolitan.
Another early and well-founded generalisation is the statement of
Linnæus that the plants common to the old and the new world are all
of northern range. Buffon made the same remark about the animals,
and offered the probable explanation—viz., that since the two great
land-masses approach one another only in high latitudes, it is only
there that animals have been able to cross from one to the other.
In the nineteenth century theories involving prodigious changes of
land and sea were much in the minds of naturalists. Darwin lost his
temper (a rare thing with him) over the land-bridges, hundreds, or
even thousands, of miles long, which were created in order to explain
trifling correspondences in the population of distant countries. A
belief in the comparative stability of the great continents and
oceans has since prevailed, and it is now recognised that the means of
dispersal of species are greater than was once supposed.
The discovery, about the year 1846, of the marks of ancient glaciers
in all parts of northern Europe, and the acceptance of an Ice Age, had
a still greater influence upon the teaching of naturalists. Edward
Forbes[46] put forth a glacial theory to account for the present
distribution of plants of northern origin. Glacial cold, he maintained,
had driven the arctic flora far southward. When more genial conditions
returned, most of the northern plants retreated towards the Pole, but
some climbed the mountains and gave rise to an isolated alpine flora.
Darwin, whose unpublished manuscripts had anticipated Forbes's theory,
believed that the whole earth became chilled during the Ice Age, and
that the fauna and flora of the temperate zone reached the tropics. His
argument, which is contained in chap. xi. of the _Origin of Species_,
is now generally accepted in principle, though opinions differ on many
points of detail. Some think that he extended too widely the effects
of glacial cold, exaggerated the resemblance of the arctic and alpine
fauna and flora, and attributed the extinction of the northern species
in the intermediate plains too exclusively to climatic causes.
One paragraph in the extremely condensed discussion on geographical
distribution which we find in the _Origin of Species_ calls attention
to the dominance of forms of life "generated in the larger areas
and more efficient workshops[47] of the north." The power which
inhabitants of the great northern land-mass of the old world, and
in a less degree those of North America, possess, and have long
possessed, of driving out the inhabitants of the southern continents
is one of the most important factors in the peopling of the earth with
new races of land-plants and land-animals. Races of men, modes of
civilisation, religious faiths, all follow the same rule, which has no
doubt prevailed ever since land came to predominate in the northern
hemisphere and water in the southern hemisphere. In the life of the sea
and the fresh waters no dominance of northern forms has been detected.
5. _Palæontology._—We must not claim for Darwin more than a modest
share in the vast extension of palæontological knowledge which the
last fifty years have created. A profusion of new materials has been
acquired by the diligence of collectors working on a scale previously
unattempted. But though the accumulation of materials is the work
of others, the interpretation has been guided by the principles of
Darwin. The evolution of the horse has now been so fully worked out
that it would bear the whole weight of a doctrine of descent with
modification, though it could not by itself reveal the process by which
the modification had been effected.
_Darwin on Adaptations._—The adaptation of living things to their
surroundings has always been a favourite branch of natural history,
underrated only by those whose studies are little calculated to inflame
the curiosity. Many eminent naturalists have made the interpretation
of natural contrivances their chief aim. Darwin equalled the best of
his predecessors in accuracy, range, and ingenuity, while he surpassed
them all in candour. No one has done so much to vindicate the study
of adaptations from all suspicion of triviality, for no one before
him had seen so clearly how all new species arise by adaptation of
pre-existing ones. It is by adaptation that new forms of life arise; it
is inheritance which preserves old ones.
Socrates, Swammerdam, and Paley had drawn from the adaptations of
nature proofs of the omnipotence and beneficence of the Creator.
Darwin, while admitting that every organism is exquisitely adapted
to its own mode of life, believed that the adaptations have been
perfected by slow degrees, and that they cannot be proved to have
been consciously devised. This interpretation deprives the theologian
of valued arguments, but at the same time rids him of difficulties.
Even before Darwin's day some few natural theologians had the courage
to bring forward instances of the harshness of nature. Kirby and
Spence[48] thought that no injustice was done to certain predatory
insects by comparing them to devils. Others blessed the mercy of
heaven, which, after creating noxious animals, created others to keep
them in check. Darwin, when reflecting upon the odious instincts which
urge the young cuckoo to eject its foster-brothers, some species of
ants to enslave others, and a multitude of ichneumons to lay their eggs
in the bodies of live caterpillars, found it a relief to be able to
shift the responsibility to an unconscious natural process.[49]
In his autobiography Darwin remarks that he had thought it almost
useless to endeavour to prove by indirect evidence that species had
been modified until he was able to show how the adaptations could be
explained. Some of them alarmed him by their difficulty; to suppose
that the eye, with all its inimitable adjustments, had been formed
by an unconscious natural process seemed to him absurd until he had
traced a good many intermediate steps between the mere colour-spot and
the eye of the eagle. He writes to Asa Gray (September 5, 1857) that
the facts which had done most to keep him scientifically orthodox were
facts of adaptation, the pollen-masses of Asclepias, the mistletoe with
its pollen carried by insects and its seeds by birds, the woodpecker
exquisitely fitted by feet, tail, beak, and tongue to climb trees and
capture insects.
The student of adaptations has no longer a moral thesis to maintain; he
tries to understand how a contrivance acts, what advantage it confers
upon its possessor, and by what steps it was perfected. The minute
variations of species are as capricious as the form of the stones
which accumulate at the foot of a precipice; natural selection turns
fortuitous variations to account for the advantage of the species as
a builder might turn to account the shapes of the stones. Man himself
can employ variations for frivolous or even base purposes, as when he
produces toy-spaniels or bull-dogs.[50] The adjustments of organic
structures often move our wonder by their perfection. One reason why
they so far exceed the adjustments made by wind, frost, or moving water
is that the process has been so protracted; in a worm or an insect we
see the last stage of an adaptation which has been continuously at
work for untold geological periods. Another reason is that the thing
adapted is alive, sensitive, and capable of responding to the subtlest
imaginable influences.
_Darwinism and Non-biological Studies._—The theory of organic
evolution has already produced a visible effect upon non-biological
studies. Bagehot has applied Darwinian principles to the interpretation
of history and politics. Philologists recognise a process very like
that of natural selection in the modification of words. The usages
of language are inherited from generation to generation; one idiom
competes with another, that persisting which best suits the temper
or the convenience of the nation. Philology has like zoology its
chains of descent, its breeds or dialects, its species or languages,
its fossils (dead languages), its dominant and declining forms, its
vestiges (such as letters, still retained, though no longer sounded).
Psychology is already in part experimental and evolutionary, and seems
as if it would attach itself more and more closely to physiology,
detaching itself in the same measure from metaphysics. The change may
be attributed to two growing convictions: (1) That the experimental
method is more trustworthy than the speculative; and (2) that the mind
of man is not a thing apart, but an enhanced form of powers manifest in
the lower animals. Sociology finds its most practicable and its most
urgent sphere of work in the problems of selection and race, which are
naturally examined in the light of Darwinian principles. The new study
of Comparative Religion aims at the impartial examination of all forms
of religious experience, and is evolutionary in proportion as it is
scientific. One of its conclusions, by no means universally accepted
as yet, is the recognition of conscience as "the organised result of
the social experiences of many generations" (Galton). Comparative
Religion can already show in outline how by slow degrees magical rites
passed into polytheistic worship, how polytheism became simplified and
elevated, and how ethical motives at length became influential if not
predominant.
Pasteur's Experimental Study of Microbes.
The same difficulty arises with Pasteur as with Darwin; his life-work
has already been described often and well. Readers unversed in science
have only to turn to the _Vie de Pasteur_, written by his son-in-law,
Vallery-Radot, to find a luminous account, giving just so much detail
as makes the discoveries intelligible and interesting. If shorter
sketches are demanded, they exist. We must therefore above all things
be brief, and content ourselves with reminding the reader of facts
which, in spite of their recent date, are as well known as anything in
the history of science.
Chemists will claim Pasteur as one of their number, and we do not
dispute the claim. Trained in experimental methods by the chemical
laboratory, he devoted his best powers to the study of living things,
and, without ceasing to be a chemist, became one of the greatest of
biologists.
Pasteur's chief work was of course the experimental investigation of
living particles which float in the air—what we may call _live dust_.
Before his day such particles had been seen, named, and classified;
some few had been studied in their action and effects. Most of them
are plants of low grade, simplified to the last point for the sake of
minuteness, on which their ready dispersal depends.
_Yeast._—Van Helmont, early in the seventeenth century, when the
microscope had not yet become an instrument of research, attempted to
investigate the fermentation of beer, and made acquaintance with the
properties of the gas which is evolved, his _gas silvestre_, which
was afterwards called fixed air, or carbonic acid. Leeuwenhoek about
1680 examined yeast by his microscopes, and discovered that it is made
up of globules which often cohere, and that these globules give off
bubbles of gas. Then comes a long interval, during which nothing was
done to elucidate the process of fermentation. It was not till 1837
that Caignard-Latour and Schwann, independently of each other, showed
that yeast-globules multiply by budding, and are therefore to be set
down as living things, probably plants of a simple kind. Twenty years
more passed without sensible progress; during this time chemists were
striving to prove that the alcohol was produced by contact-action, and
that the globules were of no practical importance. By the year 1860
Pasteur was engaged upon the problem. It is well known that he arrived
at a firm conviction that living yeast-cells are essential to the
production of alcohol. It has since been discovered that the enzyme
(unorganised ferment of older writers) secreted by living yeast-cells
can change sugar into alcohol after the cells themselves have been
destroyed, and that other plants besides yeast-cells secrete the same
enzyme when deprived of oxygen.
_Bacteria._—Another and even more important chapter in the history of
air-wafted organisms was opened by the indefatigable Leeuwenhoek. In
1683 he wrote a letter to the Royal Society which makes mention for
the first time of bacteria, which he found upon his own teeth, and
described as minute rods; some of them moved with surprising agility.
For nearly two hundred years little more was done. A few bacteria
were named and classified, and there the matter rested until Schwann
proved experimentally that putrefaction is just as much the work of
living microscopic organisms as alcoholic fermentation. In 1857 and the
following years Pasteur not only confirmed the work of Schwann, which
had been received by the majority of chemists with distrust, but went
on to show that the lactic, butyric, and ammoniacal fermentations also
depend upon the activity of bacteria. The happy thought struck him
that they might be studied alive—a possibility which he soon realised
in practice, and upon which the new science of bacteriology largely
rests. From about the year 1873 he began to occupy himself seriously
with contagion, which he suspected to be connected with specific
aerial germs. Davaine and others had years before observed in the
blood of sheep and cattle which had died of "charbon" (anthrax) minute
"bâtonnets" (bacilli). Pasteur's published results induced Davaine to
ask whether his "bâtonnets" might not be the cause of "charbon." Again,
it was Pasteur's results which induced Lister to make experiments
in the field of antiseptic surgery. Pasteur wasted no time upon the
curiosities of bacterial life. His first studies on fermentation
suggested that specific diseases may be propagated by microscopic
germs, and that such cases of spontaneous generation as had hitherto
escaped refutation might be explained by the access of live dust. The
identification and biological history of the organisms interested him
only as a step towards sure methods of controlling, and, if necessary,
destroying, them; of mitigating their virulence by inoculation; of
rendering animals immune against them; or of stamping out the disease
by isolation. All this is happily too well known for repetition here.
The story, with its many dramatic incidents, can be read in the pages
of Vallery-Radot.
Hardly less important than the bacteria which destroy life or endanger
the products of human industry are the beneficent forms, some of
which have in all ages co-operated with man, while others can only
be employed by those who possess knowledge and skill. None are so
important to our welfare as the bacteria which renew the fertility of
the soil. But for the soil-bacteria farm-yard manure would be useless
to the crop, for it is they which render it fit for assimilation.
Now the bacteria of the soil have their natural enemies, the most
mischievous being certain Protozoa, such as Amœba and its kindred.
As soon as this fact was grasped, likely remedies were thought of;
indeed, one remedy was suggested without any guidance from theory by a
vine-grower of Alsace, who treated his soil with carbon disulphide to
destroy phylloxera, and found that in so doing he had notably enhanced
its fertility. Heating to the temperature of boiling water destroys
the soil-protozoa and at the same time the bulk of the soil-bacteria.
The bacteria, however, soon multiply more than ever by reason of the
absence of their enemies, and a soil cleared of protozoa yields for
a few years appreciably richer crops. Of other useful bacteria the
briefest notice must suffice. Wine, beer, cheese, and tobacco owe to
certain of them distinct flavours, for which the customer is willing to
pay high. Leather in certain stages of manufacture, indigo, and woad
require the access of other forms. If we also bear in mind the part
which yeast plays in the every-day manufacture of bread, wine, and
beer, and the part which the vinegar-mould plays in the manufacture
of acetic acid, we shall get some notion of the industrial importance
of the various micro-organisms. Not a little of the control which we
exercise over them we owe directly or indirectly to Pasteur.
The career of Pasteur exhibits a striking unity. His first research,
which dealt with a subject so remote from the ordinary studies of the
biologist as the crystalline forms of tartrates, made him acquainted
with activities, hitherto unsuspected, of minute forms of life. The
hope of aiding the industries of Lille, Orleans, and France kept
him long engaged upon ferments. If he turned aside to examine the
superstition of spontaneous generation, it was to protect his methods
from misconstruction. An apparent break in his programme of work was
forced upon him by the silkworm pestilence. It proved to be no real
break, for pébrine and flacherie were both bacterial diseases. At a
comparatively early date (1863) he wrote that his chief ambition was
to throw light on the spread of contagious diseases; he could not then
foresee that he was destined, not only to elucidate, but in a measure
to control them. Around his tomb are inscribed words, each of which
commemorates a signal service to his fellow-men: "1848, Molecular
dissymetry. 1857, Fermentations. 1862, Spontaneous generation. 1863,
Studies of wine. 1865, Silkworm diseases. 1871, Studies on beer. 1877,
Contagious diseases of animals. 1880, Vaccination against contagious
diseases. 1885, Prevention of hydrophobia." These manifold researches
form a continuous chain, each being linked to what precedes and
follows. The devotion by which all were inspired, beginning with
devotion to science and the fatherland, ended by embracing all mankind.
* * * * *
Biology, which in the sixteenth century sent out only a few feeble
shoots, has now become a mighty tree with innumerable fruit-laden
branches. The vigour of its latest outgrowths encourages confident
hopes of future expansion.
[44] Titius of Wittenberg, who published in 1766 what is commonly
called Bode's law of planetary distances, objected to the Linnean
system on the ground that it multiplied the principle of division. (_De
divisione animalium generali_, 1760.)
[45] _Origin of Species_, chap. xiii.
[46] _Geol. Survey Memoirs_, 1846.
[47] By a curious and no doubt accidental coincidence, Darwin employs
the same remarkable metaphor which had occurred to Iordanes in the
sixth century A.D. Iordanes calls the north the _officina gentium_.
[48] Introduction to _Entomology_, Introductory Letter.
[49] _Life and Letters_, Vol. I., chap. ii.
[50] Darwin, _Variation of Plants and Animals under Domestication_,
Concluding Remarks.
CHRONOLOGICAL TABLE
1200-1850
(The date of a discovery is the date of first publication, where this
is known.)
1202. Arabic numeration introduced into Europe by Leonardo of Pisa
(Liber Abaci); it spread slowly, and did not become universal till the
middle of the seventeenth century.
1214-1294. Roger Bacon.
1265-1321. Dante.
1271-1295. Travels of Marco Polo.
1304~1374. Petrarch.
1324?-1384. Wycliffe.
1340?-1400. Chaucer.
1410. Wood-engraving introduced about this time.
1423. Earliest known block-book.
1450? Mazarin Bible, printed by moveable types.
1453. Taking of Constantinople by the Turks.
1466?-1536. Erasmus.
1471-1528. Albert Durer.
1472-1543. Copernicus.
1475-1564. Michael Angelo.
1477-1576. Titian.
1483-1520. Raphael.
1483-1546. Martin Luther.
1492. First voyage of Columbus.
1497-1498. Voyage of Vasco da Gama to India by the Cape.
1516. More's _Utopia_.
1517. Luther's theses.
1519-1521. Mexico conquered by Cortez.
1519-1522. Circumnavigation of the globe by a ship of Magellan's
squadron.
1530-1536. Brunfels' _Herbarum vivæ eicones_. Confession of
Augsburg.
1532. Peru conquered by Pizarro.
1534. Society of Jesus founded by Loyola.
1539. Bock's _New Kreutterbuch_ (without figures); 2nd ed. (with
figures) 1546.
1542. Fuchs' _Historia Stirpium_.
1543. Copernicus' _De Revolutionibus Orbium Celestium_. Vesalius'
_Fabrica Humani Corporis_.
1545. Botanic garden at Padua founded.
1545-1564. Council of Trent.
1547. Botanic garden at Pisa founded.
1551. Belon's _Histoire Naturelle des estranges poissons marins_.
1551-1587. Gesner's _Historia Animalium_.
1553. Belon's _De aquatilibus_, etc., and his _Observations de
plusieurs singularitez_, etc. (Travels in the Levant.)
1554. Rondelet's _De piscibus marinis_.
1555. Belon's _Histoire de la nature des Oyseaux_. Rondelet's
_Universæ aquatilium Historiæ pars altera_.
1564-1616. Shakespeare.
1564-1642. Galileo.
1566. Revolt of the Netherlands.
1571. Battle of Lepanto (advance of the Turks checked).
1571-1630. Kepler.
1572. Massacre of St. Bartholomew.
1576. L'Obel's _Plantarum seu Stirpium Historia and Adversaria_.
1577-1580. Drake's circumnavigation.
1583. Cesalpini's _De Plantis_.
1588. The Invincible Armada.
1596-1650. Descartes.
1600. Olivier de Serres' _Théâtre d'Agriculture_.
1601. Clusius' _Rariorum plantarum Historia_.
1605. Clusius' _Exoticorum libri decem_.
1610. Galileo'smicroscope invented about this time.
1614. Napier's Logarithms.
1618-1648. Thirty Years' War.
1620. Voyage of _Mayflower_. Bacon's _Novum Organum_.
1621. Aselli re-discovers the lacteals.
1623. C. Bauhin's _Pinax Theatri Botanici_.
1626. Jardin des Plantes founded.
1628. Harvey's _De motu cordis et sanguinis_ published, the lectures
had been delivered in 1614.
1635. French Academy founded.
1638. First authenticated cure of fever by chincona bark (in Peru).
1642. New Zealand and Van Dieman's Land discovered by Tasman.
1642-1727. Newton.
1643. Barometer invented by Torricelli.
1650? Air-pump invented by Otto von Guericke. Thoracic duct discovered
by Pecquet.
1653. Lymphatic vessels discovered by Rudbeck.
1660. Royal Society founded; incorporated 1662. Boyle's _Spring of
Air and its Effects_. Ray's _Catalogus Plantarum circa Cantabrigiam
nascentium_.
1661. Boyle's _Sceptical Chemist_. Passage of blood through
capillaries observed by Malpighi.
1665. Hooke's _Micrographia_.
1666. Académie des Sciences founded. Composition of white light
discovered by Newton.
1668. Redi on the Generation of Insects.
1669. Swammerdam's _Historia Insectorum Generalis_. Malpighi's _De
Bombyce_.
1671-1677. Grew's _Anatomy of Plants_; collected in one volume, 1682.
1672-1679. Malpighi's _Anatome Plantarum_; collected in his Opera
Omnia, 1686.
1673. Malpighi's _De formatione pulli in ovo_. Leeuwenhoek's first
paper published by the Royal Society.
1675. Greenwich Observatory founded. Velocity of light determined by
Roemer.
1676. Willughby's _Ornithologia_.
1677. Spermatozoa discovered by Hamm.
1680. Yeast-cells discovered by Leeuwenhoek.
1682. Ray's _Methodus Plantarum_.
1683. Bacteria discovered by Leeuwenhoek.
1687. Newton's _Principia_.
1691-1694. Camerarius on the sexes of flowering plants.
1702. Hydra discovered by Leeuwenhoek.
1711-1776. Hume.
1723-1790. Adam Smith.
1725. Vico's _Scienza Nuova_.
1734-1742. Réaumur's _Histoire des Insectes_.
1736-1810. Watt.
1737. Linnæus's _Systema Naturæ_; last edition by Linnæus, 1766.
Linnæus's _Genera Plantarum_.
1737-1738. Swammerdam's _Biblia Naturæ_ published; written long
before.
1738. Linnæus's _Classes Plantarum_.
1740-1761. Roesel von Rosenhof's _Insecten-Belustigungen_ begun.
1744. Trembley's _Polype d'eau douce_ (Hydra).
1745. Bonnet's _Traité d'Insectologie_ (aphids, Nais).
1748. Montesquieu's _Esprit des Lois_.
1749-1804. Buffon's _Histoire Naturelle_, the last volumes posthumous.
1752. Identity of lightning and electricity demonstrated by Franklin.
1753. British Museum founded.
1755. Black's experiments on carbonic acid and alkalis.
1759. C. F. Wolff's _Theoria Generationis_.
1760. Lyonet's _Traité Anatomique_, etc. (larva of goat-moth).
1770. New South Wales discovered by Captain Cook.
1775. Priestley's experiments on the restoration by green leaves
of air vitiated by combustion or respiration, and on
"dephlogisticated air" (oxygen). Adam Smith's _Wealth of Nations_.
1777. Spallanzani's experiments on the spontaneous generation of
minute organisms.
1781. Uranus discovered by Herschel. Leroy's _Lettres sur les Animaux_
(first collected edition).
1784. Cavendish's _Experiments on Air_ (composition of water).
1785. Hutton's _Theory of the Earth_.
1787-1789. Lavoisier's _Méthode de nomenclature chimique_ (1787) and
_Traité élémentaire de chimie_ (1789).
1789. First French Revolution. A. L. de Jussieu's _Genera Plantarum_.
White's _Natural History of Selborne_.
1790. Goethe's _Metamorphosen der Pflanzen_.
1791. Galvani's experiments on animal electricity.
1792. Sprengel's _Entdeckte Geheimniss der Natur_. F. Huber's
_Nouvelles Observations sur les Abeilles_.
1796. Cuvier on recent and fossil elephants.
1798. Jenner's _Inquiry_ (vaccination against small-pox). Lithography
invented by Senefelder.
1799. William Smith's _Order of the Strata and their Embedded Organic
Remains_.
1799-1825. Laplace's _Mécanique Celeste_.
1800. Volta's electric pile.
1807. Dalton's Atomic theory. Davy's decomposition of potash and soda.
1811. Motor and sensory roots of spinal nerves discovered by Bell.
1812. Cuvier's _Ossemens Fossiles_.
1816. Cuvier's _Règne Animal_.
1819. Electro-magnetism discovered by Œrsted. Chamisso's _De Salpa_.
1823-1831. Pollen-tubes traced to the ovule (Amici, Brongniart, Robert
Brown).
1827. Discovery of mammalian ovum by Baer.
1828-1837. Baer's _Entwickelungs-geschichte_.
1830-1832. Lyell's _Principles of Geology_.
1835. Cell-division in plants observed by Mohl.
1837. Caignard-Latour's demonstration that alcoholic fermentation is
due to living organisms.
1839. Schwann and Schleiden's cell-theory.
1840-1849. Joule's determination of the mechanical equivalent of heat.
1841. Faraday's discovery of electric induction.
1846. Discovery of Neptune by Leverrier and Adams. Agassiz and
Buckland's announcement of extensive glaciation in Scotland.
1848. Discovery of the antheridia of ferns by Suminsky.
1849-151. Hofmeister's comparative studies of the higher cryptogams
and the flowering plants.
1809-1851. Charles Darwin.
1822-1895. Louis Pasteur.
THE SUB-DIVISIONS OF BIOLOGY
Morphology:
Anatomy.
Minute Anatomy.
Comparative Anatomy.
Embryology.
Physiology (including adaptations to the conditions of life).
Psychology of Animals.
Classification.
Geographical Distribution.
Palæontology.
All these divisions, except Psychology, apply both to plants and
animals. Many other modes of division have been proposed.
BIBLIOGRAPHY
[It will be readily understood that the literature of Biology is
enormous, as a single fact will show. Half a century ago Dr. Hagen
compiled a list of books and papers relating to Entomology alone.
Though far from complete, it filled a thousand pages, and if brought
down to the present date would probably fill a thousand more. The
student who tries to follow in some detail the history of any branch of
Biology must read books in half-a-dozen languages, and work continually
in large public libraries. We shall attempt no more in this place than
to mention a few books which can be procured and read by those whose
leisure and knowledge of the subject are limited.]
History of Biology or its Sub-Divisions.
Carus, V. _Geschichte der Zoologie_. 1864 foll.
The French translation by Hagenmuller and Schneider (1880) will be
preferred by some.
Cuvier, G. _Histoire des Sciences Naturelles_. Publiée par M. de
Saint-Agy. Two vols., 1841. Taken down from Cuvier's lectures, but not
revised by him.
Though far from trustworthy (the first volume especially), this
history mentions many interesting facts, and suggests inquiries which
may be pursued with advantage.
Foster, Sir M. _Lectures on the History of Physiology_. Cambridge
Natural Science Manuals, 1901.
Green, J. R. _History of Botany_, 1860-1900. A continuation of
Sachs's History. Clarendon Press, 1909.
Sachs, J. _History of Botany_, 1530-60. English translation.
Clarendon Press, 1889.
An outline of the History of Palæontology is prefixed to Zittel's
_Handbuch der Palæontologie_, Bd. 1. (1876-80). English
translation, 1900-2.
The ninth edition of the _Encyclopædia Britannica_ often contains
useful references. See for example the articles Biology, Embryology,
Medicine, Parasitism, and Zoology.
Biographical dictionaries are of course indispensable. _The Dictionary
of National Biography_, the _Biographie_ _Universelle_, the
_Nouvelle Biographie Universelle_, the _Allgemeine Deutsche
Biographie_, and the _Biographie Nationale de Belgique_ will be
frequently consulted.
* * * * *
Among the old authors who can be read for pleasure as well as for
profit the present writer would include:—
Baker, H. _The Microscope Made Easy._ Second ed., 1743.—_Employment
for the Microscope._ 1753.
Belon, P. _Observations de plusieurs singularitez et choses mémorables
trouvées en Grece, Asie, Judée, Egypte, Arabie, et autres pays
estranges._ 1553.
—— _Histoire de la nature des Oyseaux._ 1555.
Buffon, Comte de. _Histoire Naturelle._ Forty-four vols., of which
thirty-six appeared during Buffon's lifetime. 1749-1804. Selected
passages only.
Cuvier, G. _Ossemens Fossiles._ 1812. Fourth ed. in ten vols., besides
two of plates, 1834-36. Selected passages only.
Hooke, R. _Micrographia._ 1665.
Huber, F. _Nouvelles observations sur les Abeilles._ 1792. Second ed.,
two vols., 1814.
—— J. P. _Recherches sur les mœurs des Fourmis indigènes._ 1810.
Le Roy, G. _Lettres sur les Animaux._ 1781. Reprinted, 1862.
Linnæus, C., and his Pupils. _Amœnitates Academicæ._ Seven vols.,
1749-69.
Contain interesting discussions here and there among much that is now
valueless.
—— _Lachesis Lapponica; or, A Tour in Lapland._ Translated by Sir J.
E. Smith from the original diary. Two vols., 1811.
Ray, J. _Catalogus Plantarum circa Cantabrigiam nascentium._ 1660.
Réaumur, R. A. F. de. _Histoire des Insectes._ Six vols. 1734-42.
Redi, F. _Experiments on the Generation of Insects._ Translated from
the Italian edition of 1688 by Mab Bigelow. Chicago, 1909.
Roesel von Rosenhof, A. J. _Insecten-belustigungen._ 1746-61.
Turner, W. _On Birds._ 1544. Translated by A. H. Evans, 1903.
INDEX
AFFINITY, 17, 51
Agassiz, 122
Albrecht, 61
Aldrovandi, 13
America, discovery of, 24, 112
Aristotle, 2, 16, 17 _n._, 30, 39, 45, 47, 63, 73, 102 _n._
Aselli, 21
BACON, FRANCIS, 39
—— Roger, 28
Bacteria, 137
Baer, Von, 66, 102, 104, 121, 127
Bagehot, 135
Baker, 67, 69
Barry, 106
Belon, 13
Bernard of Breydenbach, 23
Bestiaries, 6, 23
Bichât, 105
Bock, 9, 12, 37, 124
Bonnet, 45, 60
Bonpland, 118
Bossuet, 66
Brown, 105 _n._
Brunfels, 9, 12
Buffon, 40, 45, 63, 68, 71, 94 _n._, 95, 120, 130
Busbecq, 113
Butler, 67
CAIGNARD-LATOUR, 137
Caius, 19, 67
Camerarius, 48
Cesalpini, 12, 17 _n._, 34, 37, 80, 85
Chamisso, 100
Charlemagne, 25
Clodd, 65 _n._
Clusius, 111, 113
Cole, 86
Compton, 116
Copernicus, 20
DARWIN, C., 46, 66, 75, 91, 92, 120, 121, 124
—— E., 120
Davaine, 138
Descartes, 69
Dioscorides, 4
Dumas, 106
Duverney, 36
ENCYCLOPÆDIC Naturalists, 12
Erasistratus, 4
Evelyn, 111, 115, 116
Experiments of ancient Greeks, 3
FABRICIUS, 21
Fagon, 115
Flemings, 26
Fontana, 105 _n._
Forbes, 131
Fries, 17
Frisch, 37, 67
Fuchs, 9, 12
GAERTNER, 86
Galen, 4, 21
Galileo, 28
Galton, 63 _n._, 135
Geer, De, 37, 68
Gerarde, 20
Gesner, 11, 13, 17 _n._, 18, 19, 20, 113
Goethe, 80, 81, 84, 85
Greenhouses, 114
Grew, 32, 47, 86
HALES, 68, 77
Hamm, 34
Harvey, 21, 102
Hedwig, 87
Heide, 37
Helmont, Van, 77, 136
Herophilus, 4
Hofmeister, 83, 85, 108, 109, 122
Hooke, 29, 34, 37, 105
Hothouses, 114
Huber, 68, 77
Humboldt, 118
Hume, 72
Hutton, 66
INGENHOUSZ, 79
JUSSIEU, B. de, 51
—— A. L. de, 51
KANT, 120
King, 36
Kirby, 68
—— and Spence, 55, 133
LAMARCK, 46
Laplace, 120
Leeuwenhoek, 32, 40, 58, 60, 68, 86, 106, 137
Leibnitz, 45, 64
Leroy, 68, 73
Lessing, 120
Lindsay, 86
Linnæus, 48, 49, 52, 64, 80, 82, 85, 87, 90, 92, 124, 130
Lister, Lord, 138
—— M., 35, 43, 67
L'Obel, 12, 26, 124, 130
Locke, 70
Lyell, 66, 67, 94, 121
Lyonet, 34, 58, 60, 61, 67
MALPIGHI, 32, 36, 40, 45, 47, 127
Marco Polo, 23
Master, 36
Mattioli, 113
Medicine and botany, 7
Méry, 37, 38, 67
Micheli, 87
Microscope, 28, 48
Middle Ages, 5, 6, 25
Millington, 47
Mohl, 106
Montagu, 68
Montesquieu, 63, 120
Morgan, Lloyd, 74
Morison, 86
Moufet, 20
NEEDHAM, 40
Newton, 63
OLIVER and Scott, 83, 85
_Ortus Sanitatis_, 16
PALEY, 133
Palissy, 34
Pallas, 46
Parkinson, 20
Pasteur, 136
Pecquet, 22
Perrault, 36, 37, 67
Peter Martyr Angierius, 24
Physiologus, 6
Pliny, 5
Plumier, 115 _n._
Pope, 45
Poupart, 37, 38, 67
Prévost, 106
Priestley, 77
QUACKELBEEN, 113
RATHKE, 104, 127
Ray, 17 _n._, 22, 35, 38, 41, 48, 68, 124
Réaumur, 37, 40, 54, 60, 64, 68, 70, 87
Redi, 39
Rhineland, 11
Roesel von Rosenhof, 67, 69, 100
Rondelet, 13
Rudbeck, 22
SARS, 101
Saussure, De, 79
Schleiden, 105
Scott and Oliver, 83, 85
Schwann, 105, 106, 137
Seneca, 28, 113
Serres, Olivier de, 26
Smith, 35
Socrates, 133
Spallanzani, 40
Spence, 68
Spencer, 122
Sprengel, 89
Stenson, 34
Suminski, 108
Swammerdam, 29, 37, 38, 40, 70, 86, 103, 106, 133
THEOPHRASTUS, 2, 47
Titius, 124 n.
Tournefort, 38
Tradescant, 115
Trembley, 57
Turner, 18, 67
Tyson, 36
VALLISNIERI, 40
Vesalius, 20, 21
Vico, 63
Voltaire, 35
WALLACE, 120
Wallis, 22
White, 68
Wolff, 80, 82, 84, 85, 103
Woodward, 34
Wotton, 18
YEAST, 136
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