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Title: USDA Bulletin No. 816 - Street Trees
Author: Mulford, F. L.
Language: English
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Emphasis shown as _Italics_ and =Bold=.
UNITED STATES DEPARTMENT OF AGRICULTURE
=BULLETIN No. 816=
Contribution from the Bureau of Plant Industry
Wm. A. Taylor, Chief
-------------------------------------------------------
Washington, D. C. [Illustration] January 19, 1920
-------------------------------------------------------
=STREET TREES=
By
=F. L. MULFORD, Horticulturist=
Office of Horticultural and
Pomological Investigations
-------------------------------------------------------
CONTENTS
Page
Importance of Shade Trees 1
Public Control of Street Trees 6
Planning for Trees on City Streets 8
Spacing Trees 9
Conditions for Tree Growth 10
Kinds of Trees Suitable for City Streets 14
Qualities Necessary 14
Trees for Different Regions 16
Trees for Special Purposes 20
Descriptions of Street Trees 20
Culture of Street Trees 43
Selection of Individual Trees 43
Preparation of Holes 44
Planting 45
Pruning 50
Stakes and Guards 51
Later Care 52
Care of Mature Trees 53
Pruning 53
Feeding 55
Spraying 55
[Illustration]
WASHINGTON
GOVERNMENT PRINTING OFFICE
1920
=BUREAU OF PLANT INDUSTRY.=
William A. Taylor, _Chief_.
K. F. Kellerman, _Associate Chief_.
James E. Jones, _Assistant to Chief_.
J. E. Rockwell, _Officer in Charge of Publications_.
Office of Horticultural and Pomological Investigations.
SCIENTIFIC STAFF.
L. C. Corbett, _Horticulturist in Charge_.
Truck Crop Production Investigations:
J. H. Beattie.
F. E. Miller.
C. J. Hunn.
B. J. McGervey.
Irish Potato Production Investigations:
William Stuart.
C. F. Clark.
W. C. Edmundson.
P. M. Lombard.
J. W. Wellington.
L. L. Corbett.
Truck Crop Improvement Investigations:
W. W. Tracy.
D. N. Shoemaker.
Landscape Gardening and Floriculture Investigations:
F. L. Mulford.
W. Van Fleet.
Bulb Culture Investigations:
David Griffiths.
Fruit and Vegetable Utilization Investigations:
J. S. Caldwell.
C. A. Magoon.
C. W. Culpepper.
Fruit Production Investigations:
H. P. Gould.
L. B. Scott.
C. F. Kinman.
George M. Darrow.
E. D. Vosbury.
Grape Production Investigations:
George C. Husmann.
Charles Dearing.
F. L. Husmann.
Elmer Snyder.
G. L. Yerkes.
Fruit Breeding and Systematic Investigations in Pomology:
W. F. Wight.
Magdalene R. Newman.
Fruit Improvement through Bud Selection:
A. D. Shamel.
Nut Investigations:
C. A. Reed.
E. R. Lake.
Fruit and Vegetable Storage Physiology:
L. A. Hawkins.
R. C. Wright.
J. R. Magness.
J. F. Fernald.
Extension Work (in cooperation with States Relations Service):
W. R. Beattie.
C. P. Close.
UNITED STATES DEPARTMENT OF AGRICULTURE
[Illustration] BULLETIN No. 816 [Illustration]
Contribution from the Bureau of Plant Industry
WM. A. TAYLOR, Chief
Washington, D. C. [Illustration] January 19, 1920
=STREET TREES.=
By F. L. Mulford, _Horticulturist, Office of Horticultural
and Pomological Investigations_.
-----
CONTENTS
Page
Importance of Shade Trees 1
Public Control of Street Trees 6
Planning for Trees on City Streets 8
Spacing Trees 9
Conditions for Tree Growth 10
Kinds of Trees Suitable for City Streets 14
Qualities Necessary 14
Trees for Different Regions 16
Trees for Special Purposes 20
Descriptions of Street Trees 20
Culture of Street Trees 43
Selection of Individual Trees 43
Preparation of Holes 44
Planting 45
Pruning 50
Stakes and Guards 51
Later Care 52
Care of Mature Trees 53
Pruning 53
Feeding 55
Spraying 55
-----
IMPORTANCE OF SHADE TREES.
The comfort to be derived from shade trees has long been recognized. The
early settlers of this country saved fine trees about their homes, on the
village greens, along the country roads, and in the fields. Later, as
villages grew, the householders planted trees adjoining their properties,
and the result has been the beautiful elm-shaded villages of New England,
the maple-shaded towns of New York and the Ohio Valley, and the oak-shaded
streets of the Southeastern States. (Fig. 1.)
With time, the villages and towns became cities, and the woodlands were
largely destroyed. Conditions for tree growth were less favorable in the
cities, and nurseries had to be depended upon for planting material. With
these changed conditions the native trees of a region became less dominant
in the city planting and were largely replaced by those trees listed in
nursery catalogues which took the fancy of each property owner along the
street. (Fig. 2.) The quickest growing trees were considered first, and
as some of these made a big showing the first few years and were easily
transplanted, they have become the dominating trees in street planting
from the Atlantic to the Pacific and from the Great Lakes to the Gulf of
Mexico. (Figs. 2, 10, and 13.) A few have planted better and more lasting
trees (figs. 1, 3, and 4); but the tree growth on the streets of the
average town or city is ragged and unkempt in appearance, while that of
the suburb or small village is not much better unless the planting has
been done under municipal control and the plantings on a street have been
confined to a single kind of tree.
[Illustration: P15311HP
Fig. 1.--An oak-shaded street in the South. Willow oaks in Birmingham,
Ala., in late summer.]
[Illustration: P18826HP
Fig. 2.--A street with mixed plantings. The trees are of different
kinds, some unsuited for the purpose, planted at varying distances
apart, according to the inclination of the property holders. A street in
Stockton, Calif., photographed in early summer.]
[Illustration: P12515HP
Fig. 3.--American elms on a city street in midsummer. All these trees were
planted at one time at uniform distances apart by the Commissioners of
Washington, D. C.]
The advent of such civilizing agencies as the telegraph, the telephone,
the electric light, and the trolley car have added each its share toward
the mutilation or destruction of the good trees that were in existence
at the time of their coming. Faulty methods of pruning also have caused
much disfigurement and ruin. (Figs. 5 and 21.) To this mutilation has been
added the unnecessary destruction of many trees in centers of business
(fig. 6), because they excluded a little daylight, or made a store
less prominent, or were somewhat in the way of using the sidewalk for
merchandise.
In spite of all these troubles tree planting has continued because people
love trees, enjoy well-shaded streets, and are willing to make efforts to
get them. The trees on well-shaded streets are not only pleasing, but also
contribute toward the health of the community by transpiring moisture into
the atmosphere and by producing a restful effect on eyes and nerves. Red,
especially, is known to have an exciting effect on human beings, and where
city streets are well-shaded it makes less prominent those colors that
might otherwise prevail and offend.
[Illustration: Fig. 4.--Trees 18 years old on adjacent streets: _A_, Pin
oaks; _B_, ginkgos; _C_, Norway maples. Note the differences in size.]
Good shade is so appreciated that its presence adds a value to adjoining
properties. Real-estate men recognize this factor and plant shade trees
as early as practicable on land which they develop. That the beauty of a
city is improved by good street trees is becoming recognized more and more
and is finding expression in the desire of garden clubs, civic improvement
associations, and boards of trade for information on this subject.
Success in planting street trees can be attained only by planning and
controlling the planting as a whole, by selecting the most suitable
varieties, by securing trees in the best condition and planting them
properly, and by giving the necessary later care.
While towns were small, conditions for tree growth favorable, and
woodlands plenty, so that native trees were easily obtained and started,
the practice of each householder planting his own trees as he saw fit gave
good results. As towns became larger and impervious pavements took the
place of earth roads, the conditions for tree growth became more severe
and the results from the individual planting of trees less uniform. In
large cities the conditions to be met are so extreme that it has become
practically impossible for the average householder to grow street trees
successfully, or to do so only at excessive cost. Then, too, a lineman
in a few minutes often undoes what the individual has achieved with care
and years of patient waiting (see fig. 5). The trees and the lines are
both needed by the public, but when provided by individual initiative
at private expense, but trimmed for the benefit of electric lines by
employees of corporations intent on maintaining service at the least cost,
the trees suffer unduly.
[Illustration: P16692HP
Fig. 5.--A tree mutilated by linemen. An otherwise beautiful red oak in
Louisville, Ky., as it appeared in midsummer.]
In order to have good shade trees at a reasonable cost which receive
timely and efficient attention, with the effective control of wire lines,
the care of the trees needs to be vested in some adequate authority.
PUBLIC CONTROL OF STREET TREES.
Providing shade on city streets is as much a municipal function as
providing lights or sidewalks and should, therefore, be cared for by
public officials. All street trees should be directly under the care of
duly appointed officers, who should be responsible for their planting
and care, as well as for their pruning or removal. Negative control by
requiring permits for planting, pruning, and removal is little better than
no control.
[Illustration: P16986HP
Fig. 6.--A desert of asphalt in the business center of a city having less
than 100,000 population.]
The officials in charge should have the necessary authority and should be
required to initiate and carry forward planting and all other needed work
connected with the establishment and maintenance of street trees. Probably
the most satisfactory way of securing supervision is through an unpaid
commission of three or five members, which in turn employs an executive
officer. In a small place a commission of three persons may be best, one
being appointed every 2 years for a 6-year term. In large places five
members may be better, and the ideal term would be 10 years. A compromise
would be a 5-year term, a new member being appointed each year. The great
need of long-term appointees is that it takes two or three years for a
member of such a board or commission to see and realize the things needed
to be done and the policies that should be carried out. Because it takes a
long time to get results in growing street trees, the policies should be
as nearly continuous as possible and the terms of the members long enough
to insure a majority of experienced persons on the board at all times.
The method of appointing the commissioners is not so important as that
each shall be selected from the territory as a whole rather than from a
part of it. In some places where the term of service is 10 years, each
one's successor is appointed by the remaining commissioners, subject to
confirmation by the court. Where this is done a member is not permitted to
succeed himself. In other places the commission is appointed by the court;
in others, it is elected by the city legislative body or is appointed by
the mayor subject to the approval of the legislative body. The important
point is to keep the administration as nearly as possible on a purely
business basis.
A good board can accomplish nothing without liberal funds. There are two
methods of providing these: (1) By an appropriation from the general tax
levy and (2) by direct assessment against the properties, collectible
with the other taxes. If the funds are provided by appropriation, a
fixed minimum, expressed in millage of the tax rate, should be provided
in the organization of the commission. This minimum should be such that
a fair amount of maintenance work can be done when no other funds are
available. Councils that appropriate money sometimes hamper boards by
withholding appropriations. Work of the nature of tree planting should
not be permitted to suffer or be lost by a year's neglect. The fund
provided by this minimum amount should not be so large that regular
additional appropriations will not be needed to carry on the work
properly, as this will give a desirable point of contact of the commission
or board with the ordinary channels of expressing public sentiment in
the district interested. The minimum appropriation mandatory should be
sufficient to prevent injury from lack of care of work already begun.
A period of minimum care and attention while a board and the people or
their representatives are coming to a new understanding of one another's
position is not necessarily a detriment, provided a reasonable maintenance
has been possible in the interim, but without such care the results are
ruinous and work would better not be started than be undertaken with the
possibility of such a period of neglect occurring.
It is probably desirable to assess the cost of tree planting against
the adjacent property owners at a proportional cost per front foot and
to provide for maintenance out of a general fund. Boulevards and other
unusual developments are sometimes maintained with satisfactory results by
regular assessments against the abutting properties.
After a proper governing board is provided, the securing of a competent
executive is a matter of ordinary business procedure. It is usually
desirable that he shall be not only a good executive but also a man with
a knowledge of trees and trained in their care, so that he may be a
competent adviser of the board as well as its executive.
[Illustration: P18857HP
Fig. 7.--Increased attractiveness due to trees on a city street, as shown
by contrasting the two sides of the thoroughfare. If trees like red oaks,
American elms, or the Eucalyptus in the distance had been used, the effect
on this wide street would have been comparable to figure 3. The trees in
the left foreground are umbrella trees. Merced, Calif.; midsummer.]
PLANNING FOR TREES ON CITY STREETS.
With the help of one who knows trees and the local conditions to be
met, the town should be studied and a suitable kind of tree selected
for each street or for a large portion of a street (figs. 1 and 3),
and as conditions warrant the plan should be carried out as outlined.
Mixed plantings of different sorts of trees (figs. 2 and 7) are not as
pleasing and effective as the use of a single species for considerable
distances. The use of only one or two kinds for a whole town is likely to
be monotonous, and it is also undesirable because the variety most used
may become subject to serious disease or insect attacks. The species and
varieties of trees suitable for city planting are few enough, if all are
used, so an endeavor should be made to include as many different kinds as
practicable, assigning one variety for a long stretch of street unless
there is a marked change in its character, in which case a change of trees
would be warranted.
Where trees are already on a street, the problem of planning for the
future is frequently much complicated, especially if there are several
kinds in good condition. Where there is but one good kind, gaps can be
replanted with young trees of that sort. If there are poor trees of a good
variety or trees of a poor or short-lived variety it would be advisable
to remove these and do all the replanting at one time, so as to have the
trees on the street as nearly uniform as possible. Where there are several
good varieties in good condition the sensible thing is to care for the
trees that are there and then, after careful study, decide on one variety
for all future plantings on that street.
[Illustration: P14631HP
Fig. 8.--Trees 20 feet apart that should be at least 60 feet apart.
Sycamores in Washington, D. C., as they appear in late winter.]
SPACING TREES.
A common fault in all street planting is to put the trees too near
together. (Fig. 8.) This is more evident where the work has been done by
the abutting property owners than by municipalities.
After trees are started and have attained some size it is extremely
difficult to get them removed, even where the good of the remaining trees
demands it. The removal of a fairly good tree merely because it is short
lived in order to make room for a good one that will be permanent does not
appeal to the average citizen. Where trees which have been planted by the
property holder come under city control a strong feeling of proprietorship
still remains, which is outraged by the suggestion of the removal of even
poor trees. Where all the work is under city control good work is often
hampered by a strong public sentiment against the removal of trees, even
though they are poor or crowding.
Because of this difficulty it is extremely important that young trees be
planted farther apart than at that time seems reasonable. If they are
planted as far apart as is proper for mature trees the distance will be
so great as to make planting seem a joke. If they are planted half the
distance apart they should be when mature, good results would follow if
the intermediate trees were removed when they nearly touch those to be
left. As the intermediate trees would probably not be removed, or not
until too late for the good of the remaining ones, planting had better
be sufficiently far apart in the beginning to avoid the necessity of
later removals. In the beginning the trees will be too far apart and when
mature too close together, but it seems to be the alternative imposed by a
misguided public opinion.
There is scarcely a community that would permit the removal of
interplanted trees from a street of fine elms, oaks, or other worthy
varieties without a protest that would be the almost sure political
death of the administrative authorities responsible, no matter how great
the need or how much expert support they might have. If short-lived
intermediate trees were used they would not be likely to be taken out
before they died, and they probably would not die before they had
irreparably injured the permanent trees. The removal of surplus or
interplanted trees can be made with least shock to the community by
gradually narrowing the tree tops by severe pruning from year to year on
the sides next the permanent trees until finally they are so narrow they
may be removed and leave only small openings between the permanent trees.
Even this method will not materially lessen the public protest at the
final removal.
A common practice is to set street trees 35 feet apart. If it were
practicable to remove one-half the trees at the proper time this would be
a good distance, but in the eastern half of the United States and on the
Pacific slope 50 feet apart is close enough for most varieties, and for
the larger growing trees 60 to 70 feet would be better.
CONDITIONS FOR TREE GROWTH.
In order to grow, trees must have a soil of suitable texture, in proper
mechanical condition, that contains sufficient available mineral elements
and plenty of organic matter, and, last but not least, a constant supply
of moisture and air. In addition to these there must be in active growth
in the soil many forms of organic life that are in various ways preparing
the material in the soil for the use of the larger plants. Not only must
these things be present, but others that are deleterious must be absent,
whether the substance is hurtful in itself or whether it is an excess of
one that is otherwise beneficial.
Above the soil three things must be present--air, sunlight, and
moisture--and, as in the soil, harmful things must be absent in order to
have success. Among the deleterious substances are sulphur and other fumes
and soot and other products from incomplete combustion.
[Illustration: P14633HP
Fig. 9.--The irregularity in the size of the trees shown is due to a
part of the first planting having been killed by illuminating gas from
defective pipes. Norway maples as seen in Washington, D. C., in late
winter.]
Some of the more obvious things with which a city tree has to contend are:
Water-tight pavements, both on the sidewalk and street, that prevent the
admission of air and water; the removal of the topsoil in street grading,
thus forcing the tree to exist on the good soil provided in the hole;
careless digging near the tree for gas, water, and electric service, and
especially for the placing of curb-stones; the saturation of the soil with
illuminating or sewer gas from defective pipes (fig. 9); the pouring of
salt water from ice-cream freezers into gutters, where it may find its way
into the soil near tree roots; the gnawing of the trunks by horses; and
the cutting of the tops by linemen and tree trimmers.
Because of the uncongenial conditions for the growth of trees on city
streets comparatively few kinds are satisfactory for such use. Among
those available are some that will grow under extremely trying conditions.
Kinds can be found that will thrive wherever it is suitable for human
beings to live. If it is impossible to grow trees on a street, as a health
measure that street should be closed for human use until conditions are so
improved that it will support trees.
[Illustration: P15298HP
Fig. 10.--A business center relieved by a parking with Carolina poplars.
Macon, Ga.; late summer.]
More kinds will thrive under suburban conditions where only a small
portion of the roadway is covered by an impervious coating, where the
parking spaces are liberal, and where the street is lined with open lawns
than under the conditions in a city, where the street is covered with a
water and air proof coating and the sidewalks with an impervious material,
where parking spaces are limited, and where adjoining lawn areas are small
or lacking. By a careful selection of kinds, all conditions in a city can
be met. In some places bad conditions could have been improved greatly by
a little forethought; in others, such conditions can be bettered. These
details, like many other matters connected with city planning, have been
ignored, but should be considered immediately, especially by villages and
small cities. Figure 6 shows how an opportunity for creating a beauty spot
has been lost sight of, while figure 10 shows how a city has utilized less
ground to increase the comfort and attractiveness of its business center.
[Illustration: P15278HP
Fig. 11.--A street well proportioned in width of roadway, sidewalk, and
parkings, with willow oaks on the left, American elms on the right, and
young Carolina poplars near the roadway that should be removed. Columbus,
Ga.; midsummer.]
[Illustration: P14359HP
Fig. 12.--A street with too much pavement and too little parking space.
Carolina poplars in Baltimore, Md., in midautumn.]
A common mistake in ambitious young cities and many old ones is to pave
more of the width of the street for traffic purposes than, is likely ever
to be needed. By reducing the roadway and throwing the remainder into
liberal parking spaces much is added to the attractiveness and comfort
of a city. A contrast in the two methods of treatment is illustrated
in figures 11 and 12. The recommendation that the roadway prepared for
travel be made narrow is not to be interpreted as a reason for lessening
the area dedicated to the public use; in fact, in most cities, especially
in the northeastern quarter of the United States, too little space has
been reserved from houseline to houseline (fig. 13). By reserving more
room between the houses and the street for use as lawns and gardens the
conditions would be made more livable, opportunity would be offered for
widening the public way without prohibitive expense if traffic or business
demanded it, and the growing of street trees would cease to be a serious
problem.
[Illustration: P16842HP
Fig. 13.--A street with too little room from houseline to houseline. Note
the more attractive appearance of the side with trees. Norway and silver
maples in Frederick, Md., in midsummer.]
KINDS OF TREES SUITABLE FOR CITY STREETS.
QUALITIES NECESSARY.
Compared with the whole number of trees used for ornamental planting, the
number of kinds suitable for street planting is very small. For use under
city conditions a tree must be adapted to the climate and to the soil upon
which it is to be grown. It must have healthy foliage that withstands
dust and smoke and a root system not easily affected by unusual soil
conditions, by restricted feeding areas, or by root pruning when street
improvements are made. The top should be in proportion to the width of
the street upon which it is used, and it should be rather high headed or
easily trained to that form and of open growth without being too spreading
or sprawling.
Of minor consideration is the character of the foliage masses, whether
dark or light, heavy and somber or open and airy, and also whether they
have vivid autumn colorings. Only in the most southern parts of the
country and in western California should evergreen trees be considered
for street planting, and then only the broad-leaved evergreens, such as
magnolias and live oaks. In the North the lack of sunshine during the
short cloudy days of winter makes it desirable to admit all the light
possible. Even in the South the question of sunshine should be considered
when selecting varieties.
[Illustration: P12536HP
Fig. 14.--Narrow upright trees (Lombardy poplars) on a Barrow Conditions,
it is better street. Washington, D. C.; midsummer.]
Narrow streets should be planted with columnar trees (fig. 14) or
sometimes with small trees. Broad streets may be planted with spreading
trees (figs. 3 and 16), or, if provided with a central parking space, with
moderate-sized trees in the center and on the sides, or with trees on the
sides suited to the space and formal trees in the center. (Fig. 15.)
[Illustration: P18856HP
Fig. 15.--Formal trees in a central parking, but appropriate trees wanting
on the sides of the street. Canary Island date palms in Merced, Calif.;
midsummer.]
As a rule, trees native to the locality that have been successfully grown
in other cities should be given the preference. When a choice must be made
between untried native trees and those tested in a city or town under
different soil or climatic to give the native trees the first trial. There
are many native trees that are promising which have not been planted on a
sufficient scale or under sufficiently varied conditions to demonstrate
their real value for street planting over any considerable area. Many of
the trees mentioned in this bulletin may prove valuable far beyond the
areas for which they are suggested. The burr oak, the swamp white oak, the
scarlet oak, the chestnut oak, the white oak, the sour gum, and others may
be found on further trial to be as valuable as those already demonstrated
to be valuable over large areas. Those mentioned have all been tested in a
small way.
Caution should be used in selecting trees with conspicuous flowers and
those with edible fruits or nuts, as in many parts of the country such
trees are badly mutilated by the public. Even horse-chestnuts, although
the nuts are not edible, are often broken by boys clubbing the trees.
That public opinion can prevent such vandalism is in evidence all along
the Pacific coast and at a few places in the East. Every effort should be
made to create a sentiment that will protect these attractive additions to
street adornment, but where the sentiment does not exist it is better to
avoid the planting of such trees except in a limited way.
[Illustration: P15394HP
Fig. 16.--Live oaks, the handsomest southern street tree for broad street:
Biloxi, Miss.; late summer.]
Besides the native trees there are many introduced trees that have proved
valuable and many more that are worthy of trial.[1] A fair trial of
promising introduced trees should be made, and the native kinds should be
thoroughly tested.
[1] As examples of this are a number of new elms such as _Ulmus
pumila_ and _Ulmus densa_, besides lindens, poplars, and _Koelreuteria
paniculata_, while _Pistacia chinensis_ is suitable for warm regions.
The Office of Foreign Seed and Plant Introduction of the United States
Department of Agriculture will be glad at any time to suggest new trees
that are promising for any region.
TREES FOR DIFFERENT REGIONS.
To simplify the discussion of kinds of street trees likely to prove
satisfactory, the United States has been arbitrarily divided into the
regions shown in figure 17. An endeavor has been made to make each
division cover an area having similar growing conditions, so that the
trees suggested will be likely to thrive in all its parts. A discussion
of the strong and weak points of the different kinds will be found with
the description of the kinds farther on in this bulletin.
_Region 1._--Region 1 comprises the mild humid portion of the northern
Pacific coast east to the Cascade Mountains, including the western
third of Washington and Oregon and a portion of northern California.
The trees native to western Europe are adapted to this region, as the
climatic conditions are quite comparable. Most of our American trees
also succeed here.
Some of the desirable varieties for street planting in region 1 are
the Oregon, Norway, sycamore, and sugar maples; California walnut;
tulip; European linden; basswood; sycamore; London plane; white and
European ashes; English and American elms; English, red, and pin oaks;
ginkgo; and the black locust.
[Illustration: Fig. 17.--Outline map of the United States, showing the
regions within which essentially similar conditions for tree growth exist.]
_Region 2._--Region 2 is that portion of California lying between
the Sacramento and San Joaquin Valleys and the Pacific Ocean. Many
varieties of trees will succeed here if given water. Because of the
lack of water, unless specially irrigated the more drought-resistant
species should be used.
Among the deciduous trees useful for this region are the London plane;
the California and common sycamore; English, Huntingdon, and American
elms; Oregon, Norway, sycamore, and English maples; white, green, and
European ashes; red, English, and pin oaks; European linden; basswood;
California walnut; honey and black locusts; horse-chestnut; Albizzia;
and the Japanese varnish tree, or Sterculia.
Evergreen trees which will probably be successful in region 2 are the
Eucalyptus[2] in variety, acacias, rubber, magnolia, California live
oak, Victorian and poplar-leaved bottle trees, and in the southern
portions the California pepper, silk oak, and jacaranda. Palms are
much planted, but they do not make good street trees except where a
formal effect instead of shade is desired.
[2] Some cities have ordinances against the planting of certain trees
because their roots sometimes obstruct sewers. Among these trees are the
Eucalyptus in California and some of the poplars in several of the States.
_Region 3._--Region 3 comprises the Sacramento and San Joaquin Valleys.
The deciduous trees for this region are the California walnut; London
plane; California and common sycamores; Oregon, Norway, and sycamore
maples; white, European, and green ashes; red, English, valley, and
pin oaks; European linden; basswood; English and Huntingdon elms;
honey locust; and horse-chestnut. Chinaberries and Texas umbrellas are
much planted in these valleys, but are not good street trees. Olives
and palms are suitable only for formal effects, while eucalypti are
satisfactory but are liable to make trouble with defective sewers.
Acacias grow especially well in this region except in the extreme
north.
_Region 4._--Region 4 includes the country from the Sacramento and San
Joaquin Valleys to the crest of the Sierra Nevada Mountains. It varies
in elevation and correspondingly in temperature and the amount of
available moisture.
Where there is sufficient moisture, the deciduous trees recommended
for region 3, except the valley oak and possibly the California
sycamore, may be used. Where there is less moisture the thornless
honey locust, black locust, green ash, hackberry, poplars, ash-leaved
maple, and the American elm if it can be watered the first few years
may be planted. In the warmer sections the chinaberry and Texas
umbrella may be used.
_Region 5._--Region 5 comprises the hot semiarid country of southern
California and southwestern Arizona which is dependent on irrigation.
The best deciduous trees for this region are those suggested for the
drier portions of region 4. With ample irrigation the deciduous trees
recommended for region 3 might grow.
Among the evergreens the Texas palmetto, Parkinsonia, and the
Washingtonia and some other palms can be used where other trees do
not succeed. The red and desert gums may be used also in the drier
regions. With ample irrigation the evergreens suggested for region 2
should succeed.
_Region 6._--Region 6 comprises the intermountain section and extends
from the crest of the Cascade and Sierra Nevada Mountains eastward to
the eastern base of the Rocky Mountains. The region includes great
variations in growing conditions, often in very short distances. As a
whole it is semiarid, and in most places trees can hardly be expected
to thrive without more or less irrigation, although in some of the
mountain valleys and on some of the mountain slopes almost ideal
conditions for tree growth exist.
In the drier parts of the region only those deciduous trees that are
weeds under more congenial conditions can be grown. Those that can
be planted with the greatest hope of success are the thornless honey
locust, black locust, green ash, hackberry, and where the others do
not succeed, the poplars and ash-leaved maple. If it can be watered
for a few years the American elm usually can be grown, and in the
southern half of the region the Mississippi hackberry will probably
succeed. Near the southern border, on lower elevations, the chinaberry
and Texas umbrella can also be planted. In the locations most favored
naturally or where irrigation is possible, the trees suggested for
region 9 can be used.
Evergreens that may be used for the drier portions of the southern
part of region 6 are the Parkinsonia and the Texas palmetto.
Native trees may be found that will prove of greater value for limited
areas than any suggested. Cities and towns contemplating street tree
planting would do well to consult the nearest State agricultural
experiment station or the United States Department of Agriculture if
it is thought possible that something better has been found than the
trees suggested.
_Region 7._--Region 7 is the northern part of the Great Plains area
from the foot of the Rocky Mountains at about the 5,000-foot contour
line east to the ninety-eighth meridian. It is rather uniform in
general conditions, the character of soil having no wide divergence
and the elevation increasing gradually from south to north and east
to west. The rainfall gradually increases from west to east until at
about the ninety-eighth meridian the conditions are more favorable for
tree growth.
The trees to be relied on are the thornless honey locust, common
hackberry, black locust, green ash, ash-leaved maple, the poplars,
the Chinese elm, and the American elm if it can be watered the first
few years after transplanting. The mossy-cup oak is another tree
worth testing in a small way, as it is native a little east of the
ninety-eighth meridian. The basswood and Norway maple would probably
succeed if supplied with plenty of water.
_Region 8._--Region 8 is the southern part of the Great Plains.
In addition to the deciduous trees recommended for the northern Great
Plains (region 7) the Mississippi hackberry, Texas umbrella, and
chinaberry may be successfully grown.
Evergreen trees that may be used in region 8 are the Texas palmetto
and Parkinsonia.
_Region 9._--Region 9 is the upper Mississippi Valley, including
the area from that already considered to Lake Michigan and south to
southern Kansas. It is more favorable to tree growth than regions 6
and 7.
Trees which will succeed here are the American elm; red, pin,
mossy-cup, and other native oaks; white ash; sycamore; basswood; and
Norway and sugar maples.
_Region 10._--Region 10 includes the northeastern part of the country
from eastern Illinois to the Atlantic Ocean, and extends southward
through the Appalachian Mountains. It is most favorable for tree
growth.
The best trees for street planting in region 10 are the red and pin
oaks, London plane, sycamore, the staminate form of the ginkgo,
basswood, tulip, Norway maple, white ash, thornless honey locust,
American elm, and in the southern portion of the region on light land
the sweet gum. The red and sugar maples are among the best trees for
suburban conditions. The hackberry will grow, but should be discarded
in favor of better varieties. The mossy-cup and chestnut oaks are
worthy of trial on gravelly soils in the suburbs.
_Region 11._--Region 11 includes the lower Mississippi Valley and the
country east of the southern Appalachian Mountains, extending from the
light lands near the South Atlantic and Gulf coasts to the northern
limits of the distinctively southern flora.
The typical street trees of this region are the willow oaks (fig. 1)
and water oaks, the former a valuable street tree, the latter good
when young but comparatively short lived, with no advantages over the
willow oak. Other good trees are the red, Spanish, laurel, Darlington,
and pin oaks, tulip, sweet gum, American elm, red and Norway maples,
and the ginkgo.
_Region 12._--Region 12 is the land near the coast from Wilmington, N.
C., to the Mexican border, exclusive of the southern part of Florida.
Good deciduous trees for this region are the willow, laurel,
Darlington, and Spanish oaks, tulip, sweet gum, sycamore, London
plane, American elm, and the staminate form of the ginkgo. The honey
locust, red or scarlet maple, Norway maple, and the hackberries are
not so good.
The live oak is the characteristic tree of region 12 (fig. 16) and is
the pride of the cities that have used it. Even though an evergreen,
it is an excellent street tree, as it is large, spreading, and open.
The palmetto and palms thrive and may be used for producing formal
effects. The evergreen magnolia is a good broad-leaved evergreen.
_Region 13._--Region 13 consists of the southern part of Florida. The
deciduous trees suitable for this section are the willow, Spanish, and
southern red oaks; American elm; Mississippi hackberry; and in the
southern half of the region the Poinciana.
Evergreen trees are better suited to region 13 than to, any other
portion of the United States except possibly southern California.
Among the best are the live and laurel oaks, evergreen magnolia,
camphor, rubber, silk oak, or grevillea, and casuarina. Eucalypti are
planted to some extent in Florida, but the climate is such that only
on the drier grounds of the interior are they likely to succeed, and
even there they are not to be compared with other excellent species of
trees that may be cultivated successfully.
TREES FOR SPECIAL PURPOSES.
In the heart of a city, where the greatest difficulty is experienced in
getting trees to grow, the ailanthus will probably thrive when nearly all
other kinds fail. The sycamore and the London plane are also good for such
places. The Carolina poplar will frequently grow under these conditions,
and its use may sometimes be warranted.
For very narrow streets the Lombardy poplar is the best tree. (Fig. 14.)
Trees suitable for use within the reach of ocean spray or on sandy lands
near the coast are the red oak and the red or scarlet maple south to
Charleston, S. C., while the sweet gum and the live oak are equally good
from Norfolk southward and along the Gulf of Mexico. The red oak, sweet
gum, red maple, and eastern live oak are all grown successfully along
the Pacific Ocean, while the California live oak can be used from San
Francisco southward. The trees that endure the most alkali appear to be
the bladder-nut tree,[3] London plane, peppermint gum,[4] blue gum,[5]
the Washingtonia and other hardy fan palms, Canary Island date palm, the
camphor tree, and _Acacia cyclops_ and _Acacia retinodes_. Only the first
two withstand severe freezing weather. The red oak and the red maple are
worth testing for these conditions.
[3] _Koelreuteria paniculata_.
[4] _Eucalyptus amygdalina_ Labill.
[5] _Eucalyptus amygdalina angustifolia_.
DESCRIPTIONS OF STREET TREES.
ACACIA.
The acacias, or wattles, are a large group mostly of small trees with
showy yellow flowers. Although much used in California, many of them are
too small to make satisfactory shade trees, and because of shallow rooting
they are injurious to sidewalks. They also stump-sprout badly. They thrive
in regions 2 and 3 and in restricted portions of regions 1 and 5.
The Australian blackwood,[6] blackwood acacia, or wattle, is a strong,
upright tree, growing to a height of 75 feet and forming a well-shaped
head. It is badly affected by citrus scale, and on this account its
planting is sometimes prohibited.
[6] _Acacia melanoxylon_ R. Br.
The black wattle[7] is a strong-growing round-headed tree that reaches a
height of 40 feet and has dark-green leaves.
[7] _Acacia decurrens mollis_ Lindl.
The green wattle[8] is a rapid-growing tree, reaching a height of 60 feet
and forming a round head with finely cut leaves.
[8] _Acacia decurrens_ Willd.
The silver wattle[9] is much like the black wattle except that its leaves
and young branches are covered with a whitish down.
[9] _Acacia decurrens dealbata_ F. Muell.
AILANTHUS.
The ailanthus,[10] or tree of heaven, is a tall, broad, handsome tree that
is especially valuable in the heart of closely built or smoky cities.
The staminate and pistillate flowers are borne on separate trees. Only
the pistillate trees should be used, as the odor of the blossoms of the
staminate ones is very objectionable for about 10 days in late spring.
These may be produced by grafting from pistillate trees or by propagating
from suckers or root cuttings from such trees if they have not been
grafted. The ailanthus may not succeed in regions 5 and 13.
[10] _Ailanthus altissima_ (Mill.) Swingle (_A. glandulosa_ Desf.).
ASH.
There are three kinds of ash trees that are useful for street planting.
The white ash[11] is a large oval-headed tree, reasonably satisfactory
on rich lands in regions 1, 2, 3, 4, 9, 10, 11, and 12, but it is better
adapted to suburban than urban conditions.
[11] _Fraxinus americana_ L.
The green ash[12] is one of the few successful trees in regions 6, 7, and
8 and may succeed in region 5. It grows well throughout the remainder of
the United States, but is of less value than other trees there. It is much
smaller than the white ash, with a broad round top.
[12] _Fraxinus lanceolata_ Borck.
The European ash[13] is a large, handsome, round-headed tree suited to
regions 1, 2, 3, and 4.
[13] _Fraxinus excelsior_ L.
CAMPHOR.
The camphor tree[14] is a large, handsome, oval-headed evergreen that will
succeed in the southern half of region 2, in regions 3, 5, and 13, and in
the warmer parts of region 12. It will endure more frost than the orange,
and where it is successfully grown it is deservedly popular.
[14] _Cinnamomum camphora_ (L.) Nees and Eberm.
CHINABERRY.
The chinaberry,[15] sometimes known as the China tree, is a small,
round-headed, short-lived tree that will grow in regions 2, 3, 5, 8, 11,
12, and 13 and near the southern edge of region 6. It is too short lived
to be considered for planting where other trees will grow.
[15] _Melia azedarach_ L .
The umbrella tree,[16] or Texas umbrella, is a small, compact form of the
chinaberry with an umbrella-shaped top. It is useful for formal effects,
as in the parking on a wide street where taller trees are used on the
side. It will grow in regions 2, 3, 5, 8, 11, 12, and 13 and in the
southern parts of region 6.
[16] _Melia azedarach umbraculiformis_ Berckmans and Bailey.
ELM.
The elms are large, handsome shade trees suitable for use over a wide
range of territory.
[Illustration: P12460HP
Fig. 18.--An American elm with crotches liable to be split by heavy winds.
Note the supporting chains.]
The American elm[17] sometimes called the white elm and water elm, is
one of the handsomest American shade trees. (Fig. 3.) It has been the
standard street tree of New England, giving to the roadsides and village
streets the characteristic appearance which is so attractive to summer
visitors.
[17] _Ulmus americana_
The American elm is tall and spreading, and where planted as near together
as is customary on streets and country roads the effect of the mature
trees is that of an arch formed by the growing together of their spreading
tops. It is of rapid growth and long lived.
This elm drops its leaves very early in the fall, but it comes into leaf
early in the spring. Because of its manner of branching it is especially
liable to be split by heavy winds. This trouble may be lessened by
selecting and planting specimens with a close, compact habit of growth or
possibly also by great care in training young trees. Two limbs separating
from one another by a very small angle, that is, when they start to grow
in nearly the same direction, make a crotch that is liable to split. (Fig.
18.) Where two limbs separate at nearly a right angle or where three or
more limbs of about equal size grow from a common point or very nearly so,
the crotch is likely to be much stronger. Careful pruning and training to
provide a proper system of branches may be especially helpful with this
elm.
Because of the attacks of the elm leaf-beetle[18] and the European elm
bark louse,[19] many handsome trees have been severely damaged or killed
before communities were properly equipped for fighting them, for with
careful spraying these insects may be kept in check. However, on account
of the existence of these pests and because they are gradually spreading
to new territory, tree planters should consider carefully whether it
is advisable to plant the elm in their localities. Where there is no
danger from these insects, this elm is one of the best of street trees.
Consultation with the nearest State agricultural experiment station or
with the Entomologist of the United States Department of Agriculture would
be advisable in order to determine this point.
[18] _Galcrucella luteola_ Mull.
[19] _Gossyparia spuria_ Mod. (Data regarding both insects furnished by
the Bureau of Entomology.)
The best specimens are to be found in the northern part of region 10,
although the elm is being grown all over the United States and is proving
a valuable street tree even in towns and villages of regions where the
rainfall is as low as 15 inches. It is not recommended for planting in
regions 3 and 5.
The English elm[20] is a tall, oval-headed, compact, handsome tree with
leaves smaller than the American elm and which stay on much later in the
fall. In regions 1 and 2 it is at its best, in the former equaling the
American elm and in the latter excelling it. It also thrives in regions 3
and 10 and in the eastern part of region 11.
[20] _Ulmus campestris_ L.
The Huntingdon elm[21] is a comparatively round-headed European variety.
[21] _Ulmus hollandica vegeta_ (Lindl.) Rend.
It is a large, handsome tree with good foliage and is more compact in
growth than the American elm. It succeeds well in regions 1, 2, 3, and 4.
The wahoo, or winged elm,[22] is native to the South Atlantic and Gulf
States near the ocean. It has larger leaves than the American elm and is
not as spreading in its growth, but it succeeds well on city streets in
regions 11, 12, and 13.
[22] _Ulmus alata_ Michx.
EUCALYPTUS.
There are a large number of species of Eucalyptus, many of which can be
used for street planting in regions 2, 3, and 5. Some cities prohibit
their planting because their roots are liable to penetrate defective
sewers, and in other cities they must be kept at least 70 feet from a
sewer, though even this distance may not prove permanently effective.
The roots of any tree are liable to find their way into a defective
sewer, but the trees mentioned are especially noticeable because of their
vigorous root growth. It may be questioned whether a tree should be
condemned for this growth, as it may be better to have a defective sewer
thus revealed than to continue a menace to public health.
Eucalypti are also being planted in southern Florida, but on account of
the moist climate there it is not to be expected that they will succeed
as well as in the other regions mentioned. They are tall, handsome,
quick-growing trees, usually bearing two kinds of leaves at some time in
their development.
The blue gum[23] is one of the best eucalypti and the one most commonly
used in California. It is tall, globular headed, handsome, and will
survive several degrees of frost, but it will not withstand the heat of
the deserts in region 5. Its roots are especially liable to invade sewers.
[23] _Eucalyptus globulus_ Labill.
The desert gum[24] is one of the trees most resistant to heat and cold,
and it makes a handsome avenue tree. It has pendent branches that have a
tendency to severe splitting with age, but with early attention this may
be overcome largely. It may prove especially valuable for region 5.
[24] _Eucalyptus rudis_ Endl.
The manna gum[25] is another Eucalyptus which withstands several degrees
of frost and makes an excellent roadside tree. Some forms shed their bark
in long bands that leave the trunks almost white. Many people consider it
a dirty tree on this account.
[25] _Eucalyptus viminalis_ Labill.
The red gum[26] grows with a broad head, is one of the most resistant of
the eucalypti to frost, drought, and heat, and succeeds wherever any of
these trees can be grown in regions 2, 3, or 5, but is most useful in
region 5.
[26] _Eucalyptus longirostris_ F. Muell.
The sugar gum[27] is a drought-resistant variety, but it does not
withstand cold. It is a common roadside tree in southern California, but
becomes straggling with age.
[27] _Eucalyptus corynocalyx_ F. Muell.
GINKGO.
The ginkgo,[28] or maidenhair tree (fig. 4, _B_), is a native of Japan
that thrives in a cool climate or a hot, moist one and succeeds in regions
1, 9, 10, 11, 12, and 13. It is extremely erratic in its behavior,
sometimes growing well, sometimes practically not growing at all, but
where it succeeds it is very disease resistant, and it withstands severe
windstorms remarkably well. The leaf is peculiar in appearance, resembling
in outline a much enlarged leaflet of maidenhair fern with a corrugated
surface. The tree is conical when young, but as it reaches maturity its
top usually fills out, making a broad, almost flat-topped, handsome tree.
Only the staminate form should be used, because the pistillate form bears
fruits the flesh of which is slippery and dangerous when it drops to the
pavement, and to some people it is somewhat poisonous to the touch. Ginkgo
trees, therefore, would need to be secured by budding or grafting from the
mature staminate form.
[28] _Ginkgo biloba_ L.
HACKBERRIES.
The hackberry,[29] or sugarberry, is especially valuable in regions 6, 7,
8, and 9, as it grows satisfactorily where there is comparatively slight
rainfall. It is also much used in region 11, but should be superseded
there by other varieties that are better. It is of moderate size with an
oblong head and of rather open growth. It is comparatively short lived.
Its leaves are much like those of the elm.
[29] _Celtis occidentalis_ L.
The name sugarberry comes from the sweet black berries that are borne
in the early fall. The tree is sometimes affected by a fungous trouble
known as witches'-broom. This trouble causes large numbers of small
sprouts to start from the affected portion, which gives the infected tree
an unsightly appearance. The hackberry should not be planted where this
trouble is prevalent.
The Mississippi hackberry[30] is a large, open, oblong-headed tree with
smoother leaves than the common hackberry. It is useful in the southern
part of region 6, in region 8, and to some extent in regions 11 and
12. It thrives well under the same adverse moisture conditions as the
common hackberry. The trunk and the large branches have little wartlike
projections of the bark scattered irregularly over them. The small twigs
are sometimes more or less spotted or winged in the same way. The tree is
rather larger than the common hackberry and apparently is less subject to
witches'-broom.
[30] _Celtis mississippiensis_ Bosc.
HONEY LOCUST.
The honey locust[31] is a large, open, round-headed, fine-foliaged tree,
admitting much light through its top. (Fig. 19.) The common form has stiff
spines 2 to 6 inches long, or even longer. There is also a form without
spines, which is the one that should be used for street planting. It is a
useful tree in regions 1, 2, 3, 9, 10, and 11, but is especially valuable
for planting in regions 6, 7, and 8, and may prove useful in region 5.
[31] _Gleditsia triacanthos_ L.
[Illustration: Fig. 19.--A street shaded with honey locusts, as seen in
late summer. Washington, D. C.]
HORSE-CHESTNUT.
The horse-chestnut[32] has handsome blossoms that are very showy, and
when in bloom an avenue of these trees commands attention. It is a close
relative of the buckeye, or Ohio buckeye, which is also a handsome tree,
though less desirable. It is objectionable because it is likely to be
broken by boys clubbing it for its nuts, which are inedible, or where
its leaves are affected with a midsummer blight which makes it unsightly
during the remainder of the season. It is a medium-sized round-headed
tree that does much better under suburban than under city conditions. It
thrives in regions 1, 2, 3, and 10.
[32] _Aesculus hippocastanum_ L.
LINDEN.
The basswood,[33] or linden, is a large round-headed tree that is
excellent for roadsides in suburban locations and does well on city
streets if the conditions are not too severe. On account of the dark upper
surface and the lighter under surface of the leaves and the sweet-scented
blossoms in early summer it is much admired. It is not as reliable as
some of the other shade trees, as when young it is sometimes attacked at
the base of the trunk by a fungous growth that kills the tree. When once
established it forms handsome avenues. It is suited to regions 1, 2, 3, 4,
7, 9, 10, and 11.
[33] _Tilia americana_ L.
The linden,[34] or European linden, has much smaller leaves than the
American linden, or basswood, with more contrast between their upper and
lower surfaces. It is not much different in size, but is a little more
compact in growth and holds its leaves longer in the fall. It is a useful
tree for street planting in regions 1, 2, 3, 4, 9, 10, and 11.
[34] _Tilia platyphyllos_ Scop.
LOCUST.
The locust,[35] or black locust, is one of the desirable street trees
in regions 6, 7, 8, and probably in region 5, as it thrives with
comparatively little moisture. It makes a moderate-sized oval head that
bears sweet-scented white flowers in late spring or early summer. Its
greatest drawback is its liability to serious injury and disfigurement
by the locust borer,[36] but with proper care this injury can be
prevented.[37] In some parts of the East it is also subject to a leaf
miner[38] that gives its foliage a burned appearance. In region 3 it holds
its seed pods for several years and thus becomes very unsightly.
[35] _Robinia pseudacacia_ L.
[36] _Cylene robiniae_ Forst. (Data furnished by the Bureau of Entomology).
[37] See U. S. Dept. of Agriculture Bulletin 787, entitled "Protection
from the Locust Borer."
[38] _Chalepis dorsalis_ Thunb.
MAGNOLIA.
The evergreen magnolia[39] is one of the few good evergreen trees for
street planting, but it is adapted only to regions 1, 2, 3, 11, 12, and
13. There are but few conditions that warrant the planting of a tree
having foliage as thick as this, because of the dense shade, which is
especially undesirable in winter. It grows to be a large oval-headed tree
and bears beautiful large white blossoms in late spring or early summer.
[39] _Magnolia grandifolia_ L.
MAPLE.
Among the maples are some undesirable trees much used for street planting
and some that are valuable only in restricted areas or under special
conditions. The maples are not as satisfactory for street planting as
usually has been supposed, few of the species being suitable for this
purpose and these only in a limited way. The ash-leaved maple, or box
elder,[40] is native to all of the country east of the Rocky Mountains
except the regions near the South Atlantic and Gulf coasts. It is a small,
quick-growing tree that will thrive almost anywhere, but it reaches
maturity early. Because of its early decay and of its being subject to
destruction by wind, it should not be used for street planting where other
trees succeed. It would be a good tree for interplanting were it safe
to risk taking out some of the trees at the right time. The objection
to using these trees is that they would be so likely to look larger
and better than the permanent trees at the time they should be removed
that public opinion would probably resent their removal. There may be
conditions requiring the use of this tree in regions 6, 7, and 8, but it
should be grown only when the other trees suggested for these regions will
not succeed.
[40] _Acer negundo_ L.
The English maple[41] is small, round-headed, with small dark-green
leaves, useful in regions 1, 2, 3, and 4.
[41] _Acer campestre_ L.
[Illustration: P20042HP
Fig. 20.--A Norway maple, as seen in late winter, showing its poor shape
when trimmed to a high head.]
The Norway maple[42] is round-headed and eventually reaches large size,
but, as compared with most of the other maples, it is slow growing (fig.
4, _C_). The persistence of its tendency to form a low head makes it
difficult to give it a high head of desirable shape (fig. 20). It is
also very thickly branched, and its foliage, being heavy and dark-green,
permits but little light to pass through. On this account it is rather
undesirable for street planting. By severe pruning of the interior of
the head this defect may be somewhat overcome. The tree is practically
disease and insect free, with the exception of a liability to infestation
by a leaf aphis[43] which produces yellow spots on the leaves and causes
them to drop prematurely; also, the honeydew which they produce is so
abundant at times as to cover the leaves and wet the sidewalk beneath the
tree, the leaves under certain weather conditions becoming blackened with
dust accumulating and a fungus growing in the secretion, thereby giving
the tree an unsightly appearance. This aphis, however, is not always
present and does not seriously injure the tree. The Norway maple comes
into leaf later than most of the other maples, but holds its leaves later
in the fall. They usually assume a bright yellow hue before they drop. The
leaves are preceded by an abundance of yellow-green blossoms. On account
of its dense shade and masses of fine fibrous roots it is difficult to
grow grass under this tree. Its good shape and attractive dark-green
foliage make it popular for street planting in spite of its dense, low
head. It will succeed in regions 1, 2, 3, 4, 9, 10, 11, and 12.
[42] _Acer platanoides_ L.
[43] _Periphyllus lyropictus_ Kess. (Data furnished by the Bureau of
Entomology.)
The Oregon maple[44] is the large-leaved maple of the northern Pacific
slope. It forms a large round head, and with its unusually large
dark-green leaves makes a very attractive street tree that succeeds well
in regions 1, 2, 3, and 4. It is valuable and worthy of more extended
cultivation on the Pacific coast.
[44] _Acer macrophyllum_ Pursh.
The red maple,[45] scarlet maple, or swamp maple is one of the most widely
distributed of American trees. It is found from Canada to the Gulf of
Mexico and west to the Rocky Mountains. Its leaves are the smallest of any
of the eastern native maples, but it grows large and the trees are usually
of rather upright outline. It is better adapted to suburban conditions
than to city streets and is one of the few trees that succeed well near
the ocean. It has bright-red blossoms before the leaves appear. The young
leaves and fruits are also red. The mature leaves begin to color early,
some branches coloring as early as the middle of July, assuming brilliant
reds and yellows and staying on later than those of the sugar maple. It is
a handsome tree that is not as much used as it deserves to be in regions
1, 9, 10, 11, 12, and 13.
[45] _Acer rubrum_ L.
[Illustration: P12542HP
Fig. 21.--Silver maples severely headed back, an improper way to treat
trees, especially silver maples, except under very unusual conditions.
Washington, D. C.; midsummer.]
The silver maple,[46] also called the soft maple, white maple, and swamp
maple, is probably more used for street planting through the whole
United States than any other tree, and with one exception it is the
least desirable. It is usually planted because it is a quick-growing
tree, but it is not more rapid in growth than several other much better
trees. There are three serious objections to its use as a street tree.
The first is its brittle wood, which at an early age is easily broken
by ordinary windstorms and causes it when a comparatively young tree to
become unsightly. The second is its shallow rooting, which has a tendency
to destroy pavements and also makes it difficult to grow grass near the
trees. The roots also will grow into sewers. The third is the tendency to
decay; the tips of the limbs frequently die, leaving the whole top of the
tree bare of leaves, and the wood decays quickly, especially if the bark
is broken. For this reason it does not stand pruning as well as most other
street trees, and it probably has been pruned more ruthlessly than any
other tree, unless it is the Carolina poplar. It should never be severely
deheaded or, as it is popularly called, "dehorned" (fig. 21), as the stubs
will practically never heal over, and from these cuts decay will start,
which in a very few years will rot the center of the limbs and trunk and
thus destroy the tree. Although it forms a large round head with an open
top and its foliage is pale green above and almost white beneath, making
a very delightful shade, on account of its weaknesses it should never be
used for street planting where other trees can be made to grow.
[46] _Acer saccharinum_ L.
The sugar maple,[47] or hard maple, is especially adapted to gravelly
soils in regions 1, 10, and 11, the northern parts of regions 2 and 3, and
the eastern and southern parts of region 9. It is oval-headed, large, and
handsome, having red blossoms which individually are inconspicuous but
which in mass are showy early in the spring before the leaves appear. The
leaves come early, but in late summer they begin to turn brilliant yellow
and red and drop before most other leaves. The sugar maple does not thrive
under city conditions, but is admirably adapted to suburban conditions.
[47] _Acer saccharum_ Marsh.
Although the sycamore maple[48] is similar in appearance to the Norway
maple, it is not a satisfactory street tree in the eastern United States.
It succeeds, however, in regions 1, 2, 3, and 4.
[48] _Acer pseudoplatanus_ L.
[Illustration: P15662HP
Fig. 22.--A sugar maple (on the left) and a white oak (on the right), each
32 years old and nearly the same size.]
OAK.
Of the trees used for street planting the oaks are best. They probably
have not been more widely planted because of the prevalent belief that
they are slow growers and because in the North they are rather difficult
to transplant. Although some of the handsomest species, like the white oak
and live oak, are slow growers, those suitable for street planting are
comparatively rapid-growing. The white oak and sugar maple shown in figure
22 are each 32 years old and although differing in shape are practically
the same size, yet the sugar maple is considered a sufficiently
rapid-growing tree to be planted frequently as a street tree, while
the white oak is seldom so used. The oaks are hardy, most of them are
long lived, and for the most part they are free from disease and insect
attacks. Some of the southern species are subject to attacks of mistletoe.
The California live oak[49] is an evergreen suitable for use in region 2
and succeeds adjacent to the ocean. It is also useful in region 3 and in
the western part of region 5. It is easily transplanted if handled young,
and especially so when planted from pots.
[49] _Quercus agrifolia_ Nee.
The chestnut oak[50] is a native of gravelly soils on eastern mountains
and is suitable for gravelly soils in suburban locations in regions 9, 10,
and 11. It is a large, handsome tree.
[50] _Quercus montana_ Willd. (formerly _Q. prinus_).
The Darlington oak[51] is a form of laurel oak especially desirable for
street planting. It is large, round-headed; the leaves are a trifle
smaller and not quite so nearly evergreen as the laurel oak. It is
found wild about Darlington, S. C., where a good form of the laurel oak
appears to have been introduced as a shade tree in the early part of the
nineteenth century. (Fig. 23.) Its range of usefulness lies in regions 11
and 12.
[51] _Quercus laurifolia_ Michx.
The laurel oak[52] is a large, oval-headed tree that is not as rugged and
irregular as the live oak, but is suitable for street planting in regions
11, 12, and 13. It has large, thick, glossy leaves, and in the warmer
regions it is almost evergreen. It is readily transplanted, but as it is
not so common in the woods as the willow oak and the water oak, it has not
been so much used as a street tree.
[52] _Quercus laurifolia_ Michx.
[Illustration: P15461HP
Fig. 23.--A Darlington oak as seen in late summer, Darlington. S. C.]
The live oak[53] (fig. 16) is probably the noblest and most majestic of
the oaks of regions 12 and 13. It is evergreen and of slow growth, but
wherever it is found, whether on streets or in public parks, it is the
pride of the people. Although an evergreen it is sufficiently open-headed
to make a good street tree. When it becomes old it is spreading and as
a rule does not form as high a head as the willow oak and the laurel
oak. Compared with other southern oaks it is difficult to transplant.
It is of sufficient merit to be used on broad streets, and especially
on boulevards, where the good of the future as well as the present is
considered.
[53] _Quercus virginiana_ Mill.
[Illustration: P14413HP
Fig. 24.--A street shaded with red oaks, Washington, D. C.; midsummer.]
The burr oak,[54] or mossy-cup oak, is native in the northeastern United
States and west of the Mississippi River on the hills lying between the
river bottoms and the prairies west to the western parts of the Dakotas
and Nebraska and central Kansas and Texas. It is a large; handsome tree
that should prove satisfactory under suburban conditions in regions 7, 8,
9, 10, and 11 and on fertile well-watered soils.
[54] _Quercus macrocarpa_ Michx.
The pin oak,[55] sometimes called the swamp oak, is a tall tree, conical
when young, oval at maturity, with a drooping habit of the lower branches.
The leaves are quite finely divided and are of a bright glossy green.
The tree comes into leaf late in the spring and holds its foliage late
in the fall. One objection to the pin oak for street planting is that on
many specimens the dead leaves hang on through the winter. It is adapted
to narrower streets than the red oak, as its habit of growth is not so
spreading. On account of the tendency of the limbs to droop, particularly
as they get older, it is desirable that a good strong leader should be
developed, so that the lower limbs may be removed from time to time as
conditions require. The pin oak thrives on wet and on heavy clay soils, as
well as on a wide range of other soils. Figure 4 shows pin oaks, Norway
maples, and ginkgos 18 years old on adjacent streets, and illustrates the
rapid growth of this oak. At the time of planting these trees the pin oaks
were thought to have the poorest location. This tree is adapted to regions
1, 2, 3, 4, 9, 10, and 11.
[55] _Quercus palustris_ L.
The red oak[56] (fig. 24) is probably the best tree for street planting
in regions 1, 9, 10, and 11 and is satisfactory in regions 6, 7, 8, and
12. It is a large, oval, open-headed tree of rapid growth. Under good
conditions a young red oak will grow 4 feet in a single season. Like the
other oaks it is slow in coming into leaf in the spring, but holds its
foliage late in the fall. The leaves usually turn a brilliant red before
they drop. It is comparatively free from insect and fungous attacks, and
it is one of the few trees really suitable for planting close to the
ocean, as it thrives on sandy lands only a few feet above high tide or
within the reach of ocean spray.
[56] _Quercus maxima_ (March.) Ashe (formerly _Q. rubra_).
The scarlet oak[57] is a large, open, round-headed tree. Its leaves are
more deeply divided than those of the red oak. As its name indicates, the
leaves turn a brilliant scarlet in autumn, being even more gorgeous than
the red oak. This tree is adapted for street planting and is especially
desirable for suburban conditions in regions 1, 9, and 10.
[57] _Quercus coccinea_ Muench.
The swamp Spanish oak[58] is adapted to regions 11, 12, and 13. It belongs
to the red oak group, but is larger than the other oaks suggested for
street planting. It is well adapted to suburban locations, but apparently
it has not been tested under severe city conditions.
[58] _Quercus rubra_ L. (formerly _Q. falcata_, and certain forms
separated by some botanists as _Q. pagodaefolia_ Ashe).
The valley oak[59] is a beautiful tree for regions 2 and 3 and the more
favorable parts of region 5. When transplanted young, especially if taken
from a pot, it is easily established where there is opportunity to water
it for a few years.
[59] _Quercus lobata_ Nee.
The water oak[60] is frequently confused with the willow oak and the
laurel oak, as these three oaks are not distinguished from one another
except by close observers of trees. It is probably more used than any
other tree in the cities of region 12 and the adjoining portions of region
11. It is the weed of the southern oaks and one of the weeds of the street
trees of the Southern States. It is comparatively short lived and seems
to be more subject to attacks of mistletoe and more easily affected by
windstorms than the willow oak, the Darlington oak, and the laurel oak.
The planting of this tree should be avoided, because it is less desirable
than the other oaks mentioned.
[60] _Quercus nigra_ L.
[Illustration: Fig. 25.--Leaves of some of the southern oaks; _A_, Live
oak; _B_, willow oak; _C_, laurel oak; and _D_, water oak.]
The willow oak[61] (fig. 1), sometimes erroneously called the water oak,
is one of the best of the quick-growing oaks for use in regions 11 and
12. It is frequently used with the water oak for street planting and in
the mind of the average planter is confused with it. It is, however, a
distinct tree, which can be distinguished readily from the water oak. It
is longer lived and is its equal in every other respect. Trees of this
variety which apparently have been planted about 80 years are found in
excellent condition, while water oaks planted at the same time have either
entirely disappeared or are showing marked evidences of decline. Figure
25 shows the characteristic appearance of the leaves of these nearly
related species of oaks. That the willow oak is readily transplanted in
the South when of comparatively large size is proved by the success with
which trees 12 feet high are dug from the woods and planted on the street
(fig. 26). In the extreme South this tree is nearly half evergreen. Its
foliage does not assume the bright colors of the trees of the red oak
class.
[61] _Quercus phellos_ L.
[Illustration: P15321HP
Fig. 26.--Recently transplanted willow oaks, showing trees taken from the
woods as they appeared near the end of the second summer. Montgomery, Ala.]
PALM.[62]
[62] The palms are treated on the basis of notes furnished by Dr. O. F.
Cook, of the Bureau of Plant Industry.
Several varieties of palms are used more or less for street planting in
regions 2, 3, 5, 12, and 13. Though sometimes effective as a formal street
decoration (fig. 27), they can hardly be considered shade trees.
PALMETTO.
Palmettos, or sabals, abound in region 12 near the coast; succeed
in regions 3, 5, and 13; live in region 2; but are seldom grown
satisfactorily close to the Pacific coast. They can be used effectively
for formal plantings along some streets, park drives, or in liberal
central parking spaces in boulevards, but they are not useful as a
substitute for shade trees. They should have then leaves and damaged roots
cut off in transplanting and should be set about 3 feet deep in their new
location.
The Carolina palmetto[63] is a native of and useful in regions 12 and 13,
where it sometimes attains a height of 60 or 80 feet. It will thrive in
regions 3 and 5, but is used less there.
[63] _Inodes palmetto_ (Walt.) Cook.
The Texas palmetto[64] is especially valuable for southern Texas, where it
is indigenous, and it is likely to succeed generally in regions 3, 5, and
12. It grows to a height of 40 feet and in appearance is quite distinct
from the Carolina palmetto, the leaf segments being much broader and less
drooping.[65]
[64] _Inodes texana_ Cook.
[65] The Texas palmetto. _In_ Jour. Heredity, v. 8, no. 3, p. 123, pl.
1917.
[Illustration: P18989HP
Fig. 27.--A formal planting on a city street. Palms with interplantings.
Redlands, Calif., in midsummer.]
The Victoria palmetto[66] is another hardy species, probably a native of
Mexico, but grown for many years at Victoria, Tex. It is similar to the
native Texas species and worthy of general planting in the same region.
A feature of this species is that the persistent leaf bases remain alive
and green for many years instead of turning yellow or brown, as in the
Carolina palmetto.
[66] Cook, O. F. A new ornamental palmetto in southern Texas. _In_ U. S.
Dept. Agr., Bur. Plant Indus. Cir. 113, p. 11-14. 1913.
WASHINGTONIA PALM.
Washingtonia palms are a very conspicuous feature of street and
ornamental planting in southern California. Two species are represented,
_Washingtonia filifera_ Wendland and _W. robusta_ Wendland. The first is
a native of the canyons and barren slopes that surround the Coachella
Valley of southern California, while the other species probably was
brought by way of the Isthmus of Panama from the region of San Jose del
Cabo, the extremity of Lower California, in the early days of travel.
The name _robusta_ alludes to the fact that this species grows much more
rapidly in height than _W. filifera_, though the trunk is more slender.
Both species are hardy and thrive well through regions 2, 3, and 5, and
also in regions 12 and 13. _Washingtonia robusta_ requires less heat than
_W. filifera_, but both will endure several degrees of frost. Even in
California _Washingtonia robusta_ is distinctly preferable for localities
near the coast. In the vicinity of San Diego the leaves of _Washingtonia
filifera_ become badly infested with a parasitic fungus that does not
attack _Washingtonia robusta_.
OTHER HARDY FAN PALMS.
The species most commonly used for street and ornamental planting in the
California coast districts is the Chinese or windmill palm.[67] This palm
has a slender trunk clothed with brown fibers, flat fan-shaped leaves,
and rather straight radiating segments. The same species is hardy at New
Orleans and Charleston, and even at Laurens, S. C., at an altitude of 600
feet, but it does not thrive in the sandy soil of Florida.
[67] _Trachycarpus excelsa_ (Thunb.) Wendl.
The vegetable hair palm,[68] a native of Spain, Sicily, and North Africa,
is similar to the Chinese palm but smaller and more compact and with
large, sharp spines on the petioles of the leaves. When young it suckers
from the base, like the date palm, so that clusters of it may be formed.
[68] _Chamaerops humilis_ L.
The Guadeloupe Island palm[69] is one of the most popular species in
southern California in the region of Santa Barbara, Los Angeles, and San
Diego. This palm is a native of Guadeloupe Island, of! the coast of lower
California, and is not known to occur elsewhere in the wild state. It
is well adapted to the cool coast climate of California, but not to the
interior valleys. It is smaller than the Washingtonia palms, with a rather
short trunk, 15 to 20 feet high, and a dense crown of fresh green leaves.
[69] _Erythea edulis_ (H. Wendl.) S. Wats.
The California blue palm,[70] formerly placed in the same genus with
the Guadeloupe Island species, is very distinct in habits as well as
in general appearance, having bluish or grayish green leaves, strongly
toothed petioles, and long, slender inflorescences. The trunk is very
robust, often 2 to 3 feet in diameter, and is said to attain a height
of 30 to 40 feet in Mexico. Several of these features are shared with
the Washingtonia palms. It also has the ability to grow in the dry, hot
interior valleys (regions 3 and 5). In Texas the blue palm has proved
hardy at San Antonio, and even as far north as Austin.
[70] _Glaucothea armata_ (formerly known as _Erythea armata_). See Cook,
O. F., Glaucothea, a new genus of palms from Lower California. _In_ Jour.
Washington Acad. Sci., v. 5, p. 236-241. 1915.
DATE PALM.
The Canary Island date palm[71] is the most popular palm for park or
street planting, being more hardy than the true date palm, larger and more
vigorous in growth, and producing no suckers from the base of the trunk.
Well-grown specimens in the California coast districts (region 2) with
trunks from 2 to 3 feet thick and immense crowns of spreading deep-green
leaves are among the most imposing forms of plant life. Though less robust
in other regions, the species is very hardy and adapted for planting
anywhere in the palm belt (regions 3, 5, 12, and 13).
[71] _Phoenix canariensis_ Hort.
The true date palm[72] is adapted to the warmer parts of regions 3 and 5,
but it is much inferior to the Canary Island species for ornamental use
because the foliage is less attractive, due to its habit of sending out
suckers from the base of the trunk.
[72] _Phoenix dactylifera_ L.
THE COCONUT AND ITS RELATIVES.
The true coconut palm is confined to a narrow belt along the coast of
southern Florida, but other species of cocos are planted in the coast
districts of California. The species that is most prominent in park and
street plantings around San Diego, Los Angeles, and Santa Barbara is
usually known as _Cocos plumosa_ or _Cocos romanzoffiana_, and is a rather
tall, slender palm with a long-jointed trunk about 1 foot in diameter
and long, spreading, feathery, deep-green leaves. Another series is
represented by _Cocos yatay_ and several similar species, often called
_Cocos australis_ in nursery catalogues. They have short, thick trunks,
very glaucous grayish or bluish foliage, and fleshy edible fruits, highly
flavored, somewhat like pineapples. These gray-leaved species are very
hardy. Another coconut relative is the Chilean molasses palm,[73] which
has a massive trunk 3 or 4 feet in diameter, specimens of which are
growing at a few places in California.
[73] _Jubaea chilensis_ Baill.
OTHER PINNATE PALMS.
The amethyst palm, a native of Australia, is commonly planted in
California. It usually appears in lists and nursery catalogues as
_Seaforthia elegans_ or _Archontophoenix alexandrae_, but it is now
recognized as distinct from both of these species and has received a new
name, _Loroma amethystina_. It is the only pinnate-leaved palm, except
certain species of Phoenix and Cocos, that grows freely in the open air
in the coast districts of California, from Santa Barbara to San Diego.
In habit and general appearance Loroma is more like the royal palm,
though with a smaller trunk and fewer leaves. The pinkish purple drooping
inflorescence is very attractive and develops into a large cluster of
scarlet berries.
The royal palms, species of Roystonea, are perhaps the most striking
ornamental members of the whole group. They can be grown in southern
Florida and even exist in the wild state in some of the hammocks below
Miami.
PEPPER TREE.
The California pepper tree[74] is much used in regions 2 and 3 and in the
western part of region 5. It is a moderate-sized broad-headed tree with
fine foliage, which gives it a light, airy appearance. During the fall
and winter it is covered with scarlet berries, which in contrast with the
persistent foliage produce a pleasing effect.
[74] _Schinus molle_ L.
[Illustration: Fig. 28.--A pavement heaved by the roots of poplar trees.]
POPLAR.
Poplars are not desirable for street planting. Their wood is brittle and
easily broken by ordinary windstorms, and their roots run near the surface
and are likely to interfere with pavements, as shown in figure 28, while
those of some varieties are especially liable to make trouble in sewers
by filling them with a mass of fibrous roots if access is once gained.
Vigorous root growth is encouraged by the moisture from a leak, and the
roots ultimately find their way inside.
The southern cottonwood,[75] Carolina poplar, and the northern
cottonwood[76] are so similar in their adaptability for street planting
purposes that they will be discussed together. They are easily propagated,
easily transplanted, are quick-growing, and where they reach maturity
under normal conditions form very large oval-headed handsome trees, but
under the artificial conditions existing in cities it is necessary to
prune them quite severely when young to remove the long vigorous growths
and make the heads more compact. This pruning stimulates more vigorous
growth, which must be removed or they will form long branches with heavy
tops, that are especially liable to be injured by windstorms. The more
they are pruned the greater the tendency to an undesirable form of growth.
They begin dropping their leaves early in the summer and lose them very
early in the autumn. Their root growth is especially vigorous, so that
they are liable to make trouble in sewers in the manner already mentioned.
It is largely on this account that many cities prohibit the planting of
these trees. Except in regions 6, 7, or 8 or in locations where smoke and
fumes in the air prevent the growing of other trees, they should not be
planted.
[75] _Populus deltoides_ Marsh.
[76] _Populus virginiana_ Fouger.
The Lombardy poplar[77] is a tall columnar tree adapted for use on very
narrow streets (fig. 14). It is short lived in many places, due largely to
the European poplar canker, but otherwise is a satisfactory tree for these
conditions in all parts of the United States. The trees may be planted as
close together as 30 feet.
[77] _Populus italica_ (Du Roi) Moench.
None of the other poplars have much to recommend them for street planting.
RUBBER TREE.
The rubber tree[78] is a large-headed handsome evergreen, suitable for
regions 3 and 5 and the southern parts of regions 2 and 13 when the use of
an evergreen tree is warranted.
[78] _Ficus elastica_ Roxb.
SILK OAK.
The silk oak,[79] or Australian fern, is a large, handsome tree that
succeeds well in regions 2, 3, and 13; also in region 5 if provided with a
reasonable amount of moisture, as it stands drought remarkably well. It is
covered in early summer with orange-colored flowers.
[79] _Grevillea robusta_ A. Cunn.
SWEET GUM.
The sweet gum[80] is adapted to regions 11, 12, and 13, especially on
sandy lands. It forms an oval-headed, handsome tree with star-shaped
leaves that assume a particularly brilliant hue in the autumn. It is
better adapted to suburban conditions than to the heart of a city. Toward
the northern limits of its successful cultivation it is difficult to
transplant, while in the warmer sections of the country it can be moved
with comparative ease. It should be transplanted only in the spring.
[80] _Liquidambar styraciflua_ L.
SYCAMORE.
The sycamore[81] also called the buttonwood and buttonball tree, is a
large, open, spreading, quick-growing tree native along water-courses.
It is adapted to regions 1, 2, 3, 4, 9, 10, 11, 12, and 13 and is worth
testing in regions 5, 6, 7, and 8. Its habit of shedding its outer bark
in large flakes, leaving the white new bark showing in large patches,
makes it a conspicuous tree wherever grown. The fruits are balls 1 inch
or more in diameter and are sometimes objected to because they make dirt
when falling; also the shed bark is considered objectionable. It is such
a strong-growing handsome tree and succeeds so well under city conditions
that it is being planted more and more frequently. It will stand more
pruning and shaping than any other street tree. Without pruning it is
too large for ordinary streets unless spaced at almost double the usual
planting distance, with the trees staggered along the street instead
of being planted opposite. Its high head and open habit of growth are
distinct advantages for street planting. Its foliage, too, is a light
green, which gives an impression of airiness with the shade. It is subject
to attack by a fungus that kills the leaves while still small or partially
mutilates them, giving them an unsightly appearance. In some places this
trouble is quite serious.
[81] _Platanus occidentalis_ L.
The California sycamore[82] is a native of California adapted to regions
1, 2, 3, and 4 and portions of region 5. It is similar in general
characteristics to the sycamore.
[82] _Platanus racemosa_ Nutt.
The London plane tree[83] is one of the Old World forms of sycamore.
According to Alfred Render,[84] "the true oriental plane is rare in
cultivation, the tree usually planted under this name being _Platanus
acerifolia_" It it more compact in habit of growth and has the other good
qualities of the sycamore. It is being more and more used on city streets
and is proving satisfactory in regions 1, 2, 3, 4, 9, 10, 11, and 12. It
will probably succeed in the warmer parts of regions 6 and 7 and also in
regions 5 and 8. It is a more desirable tree for ordinary use than the
sycamore, on account of its more compact habit and comparative freedom
from disease, though it is tender in the northernmost sections.
[83] _Platanus acerifolia_ (Ait.) Willd.
[84] Bailey, L. H., ed. New York, 1916. Standard Cyclopedia of
Horticulture, v. 5, p. 2707.
TULIP TREE.
The tulip tree[85] is also sometimes called the tulip poplar or yellow
poplar, though the latter names are unfortunate, as the tree is not
a poplar or even closely related to the poplars. It is a large,
rapid-growing tree suitable for suburban conditions in regions 1, 2, 10,
11, and 12. The leaves are of unusual form, the upper half appearing to
have been cut away, leaving a notch about where it would seem the middle
of the leaf should be. The color is a light green. The roots are unusually
soft and tender, and therefore the tree needs to be transplanted quickly
and with great care. Small sizes should be planted, especially near the
northern limits of growth. It should be transplanted only in the spring.
If after transplanting it the top should die and a new vigorous shoot
should put out from the root, it would be desirable to form a new top from
this shoot rather than to transplant another tree.
[85] _Liriodendron tulipifera_ L.
CULTURE OF STREET TREES.
SELECTION OF INDIVIDUAL TREES.
Nursery-grown trees should be used for street planting, and they should
have been transplanted at least every two years while in the nursery.
This is to insure a thorough root pruning and the production of numerous
fibrous roots close to the trunk. Trees not frequently transplanted form
a few long roots that are largely cut off when the tree is dug. Trees
growing in the woods form a few very long roots, and when an attempt is
made to dig them only a little of the root next the trunk is obtained,
while most of the roots, including the fibrous ones, are left in the
ground. If woodland trees are wanted for street purposes, most kinds
should be grown for a few years in a nursery in order to form a good root
system before being planted on the streets.
In addition to a good root system, the tree should have a straight
trunk for the variety, with a good set of branches, called the head,
the bottom branches being from 7 to 9 feet from the ground. Trees which
naturally head low should be started with a higher head than those
varieties that have a tendency to an upright growth. A good head for a
shade tree is a leader or upright branch with three or more side branches
about equally spaced around the tree. The trees should be healthy, free
from scars, and also free from evidences of insects or diseases. In the
presence of insects, trees should be thoroughly fumigated along approved
methods before leaving nurseries, to insure against the introduction and
distribution of pests. Weakened vitality resulting from transplanting and
subsequent neglect will frequently invite attack by bark-boring insects
which seriously damage or kill the trees. Mulching and watering will often
prevent this damage.
Opinion as to the size to plant differs somewhat, but for average
conditions trees from 10 to 12 feet high and with trunks or stems from 2
to 2-1/2 inches in diameter[86] are very satisfactory in most varieties
used for street purposes. With such varieties as elms sycamores, and some
southern oaks, somewhat larger trees can be used equally well, while
smaller trees would be better in the regions of limited rainfall both
east and west of the Rocky Mountains and for tulip trees and sweet gums,
especially in the northern portion of their range of usefulness.
[86] Designated by nurserymen as "caliper."
PREPARATION OF HOLES.
Next to the selection of a proper variety, the preparation of the hole
is the most important detail of street tree planting. Because of the
restricted area available for the spread of the tree roots, and owing to
the artificial conditions imposed by the improvement of city streets, the
soil provided for the feeding ground of the roots of the young tree must
be liberal in quantity and of the best quality. From 2 to 3 cubic yards of
soil should be provided for each tree. It is desirable to have at least 18
square feet of opening in the sidewalk, especially if it is of concrete or
other impervious material. Trees will grow with smaller sidewalk openings,
but they are not likely to thrive so well, and it is impossible properly
to prepare a hole for planting a tree without disturbing at least this
much surface soil. The proper depth of soil is from 2-1/2 to 3 feet. A
hole 3 feet deep large enough to hold 2 cubic yards of soil has a surface
area of 18 square feet. A hole 6 feet long, 3 feet wide, and 3 feet deep
will hold 2 cubic yards of soil, will have the smallest desirable surface
area, and will be of such dimensions as will best conform to the usual
sidewalk and roadway widths and thus not interfere with traffic.
The tree hole must be so drained that water will not stand in it. If the
soil is so impervious as to hold water some artificial drainage must be
provided. That portion of the depth of a hole that acts as a cistern for
holding water is valueless as a feeding ground for roots. For every cubic
foot of soil in the bottom of a hole that might thus be made valueless by
standing water, 1-1/2 cubic feet of soil should be added by increasing the
length or width of it. Under no circumstances, however, should the depth
of available feeding ground be less than 2 feet. The deeper the roots may
be encouraged to grow, the less injury is likely to be experienced from
drought.
The soil used should be topsoil from land that has been producing good
crops. This should be well enriched with rotted manure, one part of manure
to four of soil. The addition of such fertilizers as ground bone, tankage,
fish scrap, or cottonseed meal at the rate of 1 pound to the cubic yard of
soil is also helpful. Commercial fertilizers containing mostly phosphoric
acid obtained from other substances than ground bone are not to be
recommended for use in the soil about the roots at planting time. When
used they should form a surface application, worked into the soil after
planting.
PLANTING.
If trees are shipped from a distance they should be taken at once on
arrival to some point where the roots may be carefully covered with soil;
there they should be unpacked and plenty of loose moist earth worked
thoroughly around and over the roots as fast as they are taken from
the box. This temporary covering of the roots is called "heeling in."
(Fig. 29.) The tops may be either erect or laid almost on the ground in
successive rows, the tops of one row lying over the roots of the previous
rows, the object being to cover the roots thoroughly and keep them moist
until the tree is wanted for permanent setting. Not a moment of exposure
should be permitted between the box and the soil. If the roots appear dry,
they may be dipped for a few minutes before "heeling in" in a tub of water
or in thin mud.
[Illustration: P20370HP
Fig. 29.--Trees properly "heeled in."]
[Illustration: P20000HP
Fig. 30.--Trees handled in a careless manner. The roots should have been
covered with wet canvas.]
Trees in large quantities are often packed directly in cars with a small
quantity of straw about the roots. When shipped in this way extra care
(compare figs. 30 and 31) must be exercised in taking the trees to the
point where they are to be heeled in. The wagon in which they are to be
hauled should have a tight box, and wet canvas should be tied tightly over
the load. The last is important, so that there may be no chance for the
roots to dry.
When taking trees from the ground where they have been heeled in to the
place for planting, great care must also be exercised to see that the
roots are not exposed to sun or wind, but are kept closely covered with
moss, wet burlap, or canvas until planted. Lack of care in this matter
is a greater cause of loss in tree planting than carelessness in any
other particular. One city that has its own nursery and uses largely
trees that are supposed to be difficult to move, but is careful about not
exposing the roots for a moment (fig. 31), has a loss of less than 1 per
cent. If the roots once dry the trees will die, and it takes but a short
exposure to dry the roots. The holes should be prepared well in advance
of planting, so that no time will be lost when conditions are right for
putting the trees in the ground.
[Illustration: P20350HP
Fig. 31.--A load of trees and tree boxes. The roots are packed in wet moss
and a tree is not taken from the wagon until the planter and two shovelers
are at the hole where it is to be planted.]
In regions 1, 10, 11, 12, and 13 (fig. 17) the best time for planting
deciduous street trees is the month or six weeks just preceding freezing
weather in the fall. The other desirable time for planting is as soon
after freezing weather is over in the spring as the ground is dry enough
for the mechanical operations. This should be as early as possible, as the
more opportunity there is for root growth before warm weather forces the
top into growth, the better the results are likely to be. In regions 6, 8,
and 9, where the ground freezes to a considerable depth, spring planting
is to be preferred to fall planting unless it is possible to drench the
soil thoroughly for a considerable distance around the trees at planting
time and after that to mulch the soil thoroughly and also to protect the
top from the effect of drying winter winds. Where mice abound they may be
harbored in the mulch and may girdle the tree. This may be prevented by
a collar of wire netting about the base of the trunk or by banking the
earth about it. The death of trees at the time of transplanting is due to
the drying out of either roots or tops before opportunity is given them
to become reestablished in their new locations. This drying may be due to
improper exposure at the time of digging or before packing (fig. 30), poor
packing, prolonged delay in delivery, improper handling between unpacking
and planting, or the existence of conditions conducive to excessive drying
out of the plant after setting.
[Illustration: P14340HP
Fig. 32.--A city nursery.]
The atmosphere is continually claiming a tribute of moisture from all
living plants, whether the plant is in leaf and growing or is dormant.
Growing plants, and dormant plants under normal conditions, are able to
replace this moisture by absorption through the roots. In climates where
newly planted trees may obtain sufficient soil water to replace these
losses by drying, fall planting is best. Where the plants are unable to
get sufficient winter moisture, planting would better be done only in the
spring. Where the soil freezes to a depth greater than that to which the
plant roots extend, the supply of water is cut off from the roots and the
tree will be killed by drying out through evaporation from the top. Where
winter winds are very drying and the soil moisture is limited, evaporation
from the top is likely to be in excess of that supplied by the roots and
the tree is killed in the same way.
[Illustration: Fig. 33.--Setting a tree: _A_, Measuring from the curb to
get the tree in line; _B_, filling the hole: _C_, placing the box; _D_,
fastening the box.]
In regions normally adapted to fall planting, newly set trees may be
killed by a dry autumn followed by a dry winter with, high winds or by a
cold winter with so little snow that the ground freezes below the roots.
On the other hand, trees may often be successfully planted in the fall
where such practice is not usually successful by thoroughly mulching the
soil if freezing is the sole cause of the difficulty, or by drenching the
soil thoroughly and then mulching well if lack of moisture and high winds
are the causes of the trouble. Protection from the wind by wrapping the
trunk and large limbs with burlap or some other protecting material is
also desirable.
After a liberal opening has been made in the specially prepared soil the
tree should be brought, preferably from the city's own nursery (fig. 32),
but if such a nursery has not been provided, then from among the newly
received trees that have been "heeled in" as already described.
If the tree has been well handled and the roots carefully protected it is
ready for setting. It is desirable to immerse the roots in a thin mixture
of clay and water just before putting it in the hole if there is suspicion
that the roots have been exposed. This can be done before leaving the
nursery or "heeling in" ground, but the roots must be properly protected.
Any mutilated ends of roots should be removed, the top should be severely
pruned, as described later, and the tree should be placed in the hole in
line with the other trees (fig. 33, _A_) and at such a height that after
the filling is completed it will be about an inch deeper in the ground
than it was before transplanting. The roots should be spread out in as
near their original position as practicable, and soil should be carefully
worked in about them with the fingers, so that each rootlet may come in
contact with soil and not be crowded against other rootlets. When all the
roots have been placed and covered the soil should be thoroughly trampled
or tamped to bring the roots into as close contact as possible with it.
Then more soil should be put in and the ground again tamped. Of course, in
order to get satisfactory results the soil used for planting must not be
too wet or too dry. If the soil is in such a state as to hold together in
soggy masses and not spring apart again when squeezed in the hand, it is
too wet for planting. If the soil is too dry, it will not stay in contact
with the roots during the planting operations. A soil that is too dry may
be well-watered a day or two in advance of the planting, or if excessive
dryness does not make it difficult to handle, the tree may be planted and
then be thoroughly watered. After the watering 3 or 4 inches of loose
soil should be spread over the wet ground in order to prevent undue
evaporation. It should not be trampled or pounded in any way after the
water is applied. If trees planted in moist retentive soils are watered
after planting they should be provided with a mulch of similar earth. East
of the Missouri River trees planted in soil that is in good condition
usually do not need watering at the time of planting.
Trees planted from pots, cans, or boxes should have the ball of earth
taken from the receptacle handled with care, so as not to break it further
than to loosen some of the roots on the outside of the ball; then the soil
should be as carefully placed about this ball and the loosened roots as
about the roots of trees without balls. Trees planted with balls need no
root pruning and little top pruning.
[Illustration: P20367HP
Fig. 34.--A pin oak trimmed for planting. Note the bad stubs (_A, A_) on
the left-hand side of the tree.]
[Illustration: P20368HP
Fig. 35.--A sycamore trimmed for planting. Well primed, without bad stubs.]
PRUNING.
At planting time the trees should be so pruned as to remove from one-half
to three-fourths of the leaf buds. The head should be formed in the
nursery, so that at planting time the only problem is how to reduce the
amount of prospective growth the first season without destroying the form
of the head. Specific directions are difficult, because different species
of trees are so different in their character of growth. A species that
is naturally compact in growth (fig. 34) should be pruned by removing
whole branches rather than by having the ends of branches removed. One
that is open and spreading (fig. 35) will probably need the shortening
of the longer limbs as well as the removal of interior branches. The
first pruning should be the removal of such branches as can be spared.
If enough buds can not be removed in this way without leaving the head
too open, then the shortening of the branches must follow. It is usually
necessary to remove three-fourths of the limbs to accomplish this. An
expert can do this pruning or most of it more easily before the tree is
planted than afterwards. Some additional pruning may be necessary after
the tree is set.
In addition to the pruning of the top the roots may need some cutting.
Any broken pieces or ends should be removed, making a clean cut with a
sharp knife, as new rootlets put out more readily from a cleanly cut fresh
surface than from ragged breaks. If the roots are very long, without
branches or rootlets, it sometimes makes planting easier to cut off some
of the ends. As roots are the braces by which a tree is supported in the
ground, it is undesirable to reduce their length unless some positive good
is to be gained by it.
[Illustration: P20372HP
Fig. 36.--Types of tree guards.]
The best implement for cutting small limbs is a sharp knife, and for
larger limbs a fine-toothed saw. Pruning shears are sometimes used, but
they are likely to bruise the wood. If used at all, the blade should
always be turned toward the tree so that the bruise made by the supporting
bar will be on the portion cut off. Where branches are taken off, the cut
should be close to the remaining limb, so that no suggestion of a stub
will remain. (Figs. 34 and 35.) Where ends are cut from branches the cut
should be just above a bud, and the remaining bud should point in the
direction that it is desired the limb should grow.
STAKES AND GUARDS.
Under city conditions young trees need the support of a strong stake as
well as protection for the trunk. Boys like to swing around small trees
or see the tops fly up if bent to the ground. Men find them convenient
hitching posts for their horses, and horses frequently like the taste of
the bark or tear it off for the sake of having something to do.
Guards are of many forms (fig. 36), from stakes 2-1/2 inches square set 3
feet in the ground and extending 6 feet above, with heavy-netting placed
about the tree and stapled to the stake, to heavy wooden cribs of four
stakes and intermediate slats and wrought-iron patterns of many forms.
The trees should be firmly secured to the tops of the guards so that they
will not swing against them in the wind and be rubbed. This is best done
by securing the tree in place in the guard by two loops of pieces of old
garden hose, soft leather, or rope, in such a way as not to bind the tree
too tightly while keeping it from swinging much or rubbing. The essentials
are a firm support for the tree while young with reasonable protection of
the trunk from careless depredations until the tree has reached a diameter
of 6 inches or more.
LATER CARE.
If after planting, the season is dry and it becomes necessary to apply
water, the ground should be soaked thoroughly, and as soon as it has dried
sufficiently to work up loosely it should be hoed or raked to make a good
earth mulch. A mulch of strawy manure or litter may be used in place of
the earth mulch if desired. The watering should not require repeating for
a week or more.
If the weather becomes warm soon after planting and the trees come into
leaf, wither, and droop, further pruning may save them. The reason for the
difficulty is probably that the growth of the top has been greater than
the newly formed roots can support; therefore the additional pruning is
likely to restore the balance between the top growth and root growth. At
least three-fourths of the remaining young wood should be removed. This
may leave the tree looking almost like a bean pole, but if it induces a
vigorous root growth the top can easily be re-formed.
Young trees should have an annual inspection, and all crossing branches
and any that are not well placed to form a good head should be removed.
Attention should be given also to all forks, and where two branches start
almost parallel to one another or at a small angle, making a fork liable
to split apart as the tree grows, one branch should be removed. Where
three branches start from almost the same point there is little likelihood
of their splitting apart, but with only two growing at a less angle than
30° there is liable to be trouble in the case of most kinds of trees. On
trees on which few but long shoots form, it may be well to remove the ends
of such shoots. As a rule, it is undesirable to use for street planting
trees with this kind of growth. Young trees should be trained into a
desirable shape by the use of a pruning knife each year, so that a saw
will not be necessary later. Some trees have a tendency to form too dense
a head. The interior branches of these should be removed and the head made
as open as possible while the work can be done with a knife. No attempt
should be made to alter the natural form of a tree but only to insure its
best development. A skillfully pruned young tree will show no evidences of
the pruning after three or four years.
CARE OF MATURE TREES.
PRUNING.
It is very little trouble to train a tree into a good shape by using the
pruning knife while the limbs are small, but it is usually difficult
to re-form a tree after it has grown to maturity. One who understands
tree growth, however, can often reshape the top of a neglected tree to
advantage, though many who make a business of tree trimming know so little
about it that they do more harm than good. More mature trees have been
hurt by severe pruning than have been helped. Of course, dead or dying
wood should be removed whenever it is found, no matter what the age of
the tree. This should be done by cutting off the limb back to the nearest
healthy crotch. A limb should not be cut off square across (fig. 21)
unless the tree is apparently in a dying condition and the whole top is
treated thus in an attempt to save its life. In such a case, a second
pruning should follow within two years, at which time the stubs left at
the first trimming should be cut off in a proper manner near the newly
started limbs. Healthy silver maples and willows are frequently cut in
this way, but the maples in particular would better be cut down at once
than to subject the public to the dangers of the insidious decay that
almost always follows such an operation on these trees and completes their
destruction promptly.
Trees that have been neglected a long time frequently have interfering
or crossing branches, or are too low headed or too densely headed for
the place where they are growing. Defects of this kind may be at least
partially remedied. The removal of limbs by cutting them off at a crotch
in such a manner that the wound is parallel with the remaining branch
(fig. 37) inflicts the least possible damage. Such a wound in a healthy
tree will soon heal over if the cut is made through the slight collar or
ring that is nearly always present at the base of a branch. The closer
this cut can be made to the trunk the better the appearance when the cut
is healed. The closer the cut the larger the wound, but the difference
is unimportant if the wood is well protected until it is healed. These
operations are entirely different in purpose and result from the "heading
in" or "heading back" so often practiced under the guise of tree pruning,
either from a false notion of forming a top or for the passage of wires.
Changing the form of a tree by pruning should not be attempted. Each
species has its own form or forms, and no attempt should be made to
change or distort a tree from its normal habit of growth. Successful
pruning will accentuate rather than disguise a tree's characteristics.
[Illustration: P20371HP
Fig. 37.--Part of a tree trunk showing proper and improper methods of
removing old limbs. Although healing has started on the stub (at the
right) it is likely to proceed very slowly. The nearer the cut is to the
tree the larger the wound but the less conspicuous the stub will be when
healed.]
All cuts should be made so that no stubs or protuberances are left to
prevent quick healing. Small wounds need no after treatment if the cut
is well made. Large wounds should have the wood of the center of the
cut well protected to prevent decay until the new growth has had an
opportunity to heal over the cut. An application made to the center of the
cut to preserve the wood should not be permitted to come near the cambium
layer or inner bark, especially of soft-wooded trees like the tulip and
magnolia, as the oil or other substances contained in the paint, tar, or
other covering may spread to the cambium layer and kill it. It is well not
to make any application within half an inch of the outside of the wound
unless the coating has been thoroughly tested.
Dead wood should be entirely removed, the cut being made through good live
tissue. Removing such wood frequently exposes decayed cavities, usually
from bad stubs or injuries which have started decay that has followed back
to the main limbs or the trunk. The treatment of such cavities is the
province of tree surgery and is discussed in another publication.[87]
[87] Collins, J. F. Practical tree surgery. _In_ U. S. Dept. Agr.
Yearbook, 1913, pp. 163-190, pl. 16-22. Published as Yearbook Separate
622, obtainable from the Superintendent of Documents for 10 cents in coin.
One source of trouble with a large tree that has developed with two trunks
or branches instead of three or more is the liability of their splitting
apart in the crotch. This is especially characteristic of the elm. Careful
attention to the early pruning of trees may eliminate this defect, but
when it exists in mature trees it is frequently advisable to connect the
branches by a strong chain (fig. 18) in order to prevent the limbs from
being torn apart.
FEEDING.
It is difficult to do anything to stimulate the growth of street trees
after they are once started, because usually the only uncovered area over
the roots is the small opening immediately about the tree; hence, the
importance of supplying the best of soil well enriched at the time of
planting. Sometimes a stimulation is desirable, which can be accomplished
by dissolving one-half to 1 pound of nitrate of soda in 50 gallons of
water and applying from 1 to 25 gallons of the liquid, depending on the
size of the tree. Unless the soil is damp at the time of application water
will be needed immediately afterward. This material should be applied only
when the tree is in full leaf and growing. If applied when the tree is
dormant it is likely to be leached from the soil before it is absorbed.
If applied late in the season, that is, within three months of freezing
weather, it would likely stimulate a late growth that would be liable
to be killed the following winter and might make the whole tree more
susceptible to injury from cold.
Water is one of the great needs of city trees, as the ground surface is
often almost completely roofed over with water-tight coverings. It is
usually a help for the pavement washings to drain into the parking space
where the tree is planted. If a curb is placed about the parking space,
frequent, regular watering is necessary where the ground is thoroughly
covered with water-tight pavements.
Where growing under suburban conditions, that is, with streets partially
pervious to water, liberal parking spaces, and adjoining lawns, street
trees will respond to all extra care given the near-by open spaces,
whether parkings, lawns, or gardens. If these are well cared for the trees
should have ample sustenance from them without any direct applications.
In order to prevent the soil about a tree from being packed too hard by
trampling it is frequently desirable on business streets to cover the soil
about it with an iron grating.
SPRAYING.
Street trees, like all other forms of vegetation, are subject to attacks
of insects and diseases. Because of the unfavorable conditions under which
they grow, spraying for biting and sucking insects and suitable treatment
for borers or other burrowing insects require especially careful attention.
In addition to a number of troubles common to street trees in general,
each species is liable to troubles of its own; hence, the need of
competent supervision by a trained man with an efficient outfit rather
than leaving; the work to individual initiative.
Because of the height which many street trees attain a powerful outfit is
required to spray them properly. One capable of maintaining a pressure
of 200 pounds per square inch is desirable. The type of spray required
for tall trees is different from that used on fruit trees and other
low plants. For low trees the ideal spray is a mist within a few feet
of the nozzle, application being accomplished by having the nozzles
near the foliage to be treated. For tall trees it is desirable that the
liquid should leave the nozzle in a solid stream, which is broken into
spray as it passes through the air. The material has to be projected
with sufficient force to reach the highest trees before being entirely
converted into mist, as it is impracticable to extend the nozzles into
the trees to reach the farthest portions, as is done with fruit and other
low trees. The spray can not be applied as uniformly as a mist, but it
is impracticable to climb into the tops of shade trees to cover every
part with a cloudlike spray. On the other hand, the mist spray is better
for small trees, as much injury may be done to low trees or to the lower
branches of high trees by the force of the stream from high-pressure
outfits.
It is estimated that in practice up to 95 per cent of the attacking
insects can be killed with insecticides carefully applied by the stream
method under high pressure.
In addition to the mechanical problem of satisfactorily covering high
trees with insecticides or fungicides there is the problem of selecting
materials that will be effective against the insects and diseases and
at the same time will not disfigure the paint or stone work of adjacent
buildings with which the materials must inevitably come in contact in
street tree spraying. It frequently happens that the most effective
remedies must be rejected because of the damage they would do to buildings
and that less efficient materials must be used.
Whitewashing the trunks of trees is a useless and unsightly
practice--useless, as it does not prevent the attacks of insects, and
unsightly, because it makes the trunks of the trees obtrusive when they
should be inconspicuous.
Banding with cotton or proprietary preparations may occasionally be
useful, but because such applications are so seldom helpful and because
some of the preparations result in injury due to constriction of the
trunks, it should not be resorted to except upon special recommendation of
an entomologist familiar with the existing conditions.
Details as to enemies to be expected, methods of treatment, and materials
to be used may be found in other publications[88] or may be obtained by
correspondence with the nearest State agricultural experiment station or
with the United States Department of Agriculture.
[88] See list on following pages.
* * * * *
PUBLICATIONS OF THE UNITED STATES DEPARTMENT OF AGRICULTURE
RELATING TO DISEASES AND INSECTS AFFECTING SHADE AND ORNAMENTAL TREES.
=AVAILABLE FOR FREE DISTRIBUTION.=
Control of Root-Knot. (Farmers' Bulletin 648.)
The San Jose Scale and Its Control. (Farmers' Bulletin 650.)
The Bagworm, an Injurious Shade-Tree Insect. (Farmers' Bulletin 701.)
The Catalpa Sphinx. (Farmers' Bulletin 705.)
The Leopard Moth: A Dangerous Imported Enemy of Shade Trees.
(Farmers' Bulletin 708.)
The Oyster-Shell Scale and the Scurfy Scale. (Farmers' Bulletin 723.)
The White-Pine Blister Rust. (Farmers' Bulletin 742.)
Carbon Disulphid as an Insecticide. (Farmers' Bulletin 799.)
The Gipsy Moth and the Brown-Tail Moth and Their Control. (Farmers'
Bulletin 845.)
Common White Grubs. (Farmers' Bulletin 940.)
The Blights of Coniferous Nursery Stock. (Department Bulletin 44.)
Forest Disease Surveys. (Department Bulletin 658.)
=FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS,
GOVERNMENT PRINTING OFFICE,
WASHINGTON, D. C.=
The Mistletoe Pest in the Southwest. (Bureau of Plant Industry
Bulletin 166.) Price, 10 cents.
The Death of Chestnuts and Oaks Due to Armillaria mellea.
(Department Bulletin 89.) Price, 5 cents.
New Facts Concerning the White-Pine Blister Rust. (Department
Bulletin 116.) Price, 5 cents.
The Huisache Girdler. (Department Bulletin 184.) Price, 5 cents.
Report on the Gipsy Moth Work in New England. (Department Bulletin
204.) Price, 30 cents.
A Disease of Pines Caused by Cronartium pyriforme. (Department
Bulletin 247.) Price, 5 cents.
Food Plants of the Gipsy Moth in America. (Department Bulletin 250.)
Price, 10 cents.
Dispersion of Gipsy Moth Larvæ by the Wind. (Department Bulletin
273.) Price, 15 cents.
The Cottonwood Borer. (Department Bulletin 424.) Price, 5 cents.
Solid-Stream Spraying against the Gipsy Moth and the Brown-Tail Moth
in New England. (Department Bulletin 4.80.) Price, 15 cents.
Protection from the Locust Borer. (Department Bulletin 787.) Price,
5 cents.
Principal Insects Liable to be Distributed on Nursery Stock.
(Entomology Bulletin 34, n. s.) Price, 5 cents.
The Locust Borer. (Entomology Bulletin 58, part 1.) Price, 5 cents.
Additional Data on the Locust Borer. (Entomology Bulletin 58, part
3.) Price, 5 cents.
The San Jose or Chinese Scale. (Entomology Bulletin 62.) Price, 25
cents.
Report on Field Work against the Gipsy Moth and the Brown-Tail Moth.
(Entomology Bulletin 87.) Price, 35 cents.
The Importation into the United States of the Parasites of the Gipsy
Moth and the Brown-Tail Moth. (Entomology Bulletin 91.) Price, 65
cents.
The Dispersion of the Gipsy Moth. (Entomology Bulletin 119.) Price,
20 cents.
The Green-Striped Maple Worm. (Entomology Circular 110.) Price, 5
cents.
The Oak Pruner. (Entomology Circular 130.) Price, 5 cents.
The Dying Hickory Trees: Cause and Remedy. (Entomology Circular
144.) Price, 5 cents.
Flour Paste as a Control for Red Spiders and as a Spreader for
Contact Insecticides. (Entomology Circular 166.) Price, 5 cents.
Three Undescribed Heart-Rots of Hardwood Trees, Especially of Oak.
(Journal of Agricultural Research, vol. 1, No. 2.) Price, 25
cents.
A Serious Disease in Forest Nurseries Caused by Peridermium
filamentosum. (Journal of Agricultural Research, vol. v, No. 17.)
Price, 10 cents.
The Chestnut Bark Disease. (Separate 598, from Yearbook of the
Department of Agriculture for 1918.) Price, 10 cents.
Practical Tree Surgery. (Separate 622, from Yearbook of the
Department of Agriculture for 1913.) Price, 10 cents.
Forest Tree Diseases Common in California and Nevada. (Forest
Service Unnumbered Publication.) Price, 25 cents.
ADDITIONAL COPIES
OF THIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D. C.
AT
15 CENTS PER COPY
* * * * *
Transcriber Notes
Illustrations were moved so as to not split paragraphs.
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