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.