The life of every tree depends upon its success in holding its leaves out
into the sunlight. The tree which exposes the greatest amount of leaf
surface to the sun makes the greatest growth. The shape of their tops is
a character in which trees differ widely. We shall come to know many of
them in winter time better than in summer, by the distinct shapes
revealed when the foliage is gone. In any bare tree, the purpose of all
of the branching and branching again, is plainly seen. Each twig and
branch reaches out toward the outer surface of the dome, or pyramid. Here
the buds in winter are waiting to open, when spring comes, into leafy
shoots. These will cover the tree top with a dome of green greater than
the one of the previous summer. Their work through the growing season
will lengthen every branch and every root, and add a layer of wood under
the bark of trunks and branches and roots.
The most remarkable tree shape is that of the Lombardy poplar. The tall
trunk is clothed with many short, close-branched limbs, which do not
spread, as in ordinary tree forms, but grow upright, so as to lie almost
against the main trunk. The upper branches are overlapped and crowded by
those below them, and so on down the trunk. The result is a tree shaped
like a capital I. In summer time, the heart-shaped leaves cover the twigs
on the outside of this spire, but the beauty of the tree top is marred by
the dead branches which have been smothered by the crowding.
A young Lombardy poplar is handsome as it stands covered with its
twinkling leaves. It grows rapidly, and is especially striking and
effective in clumps of round-headed trees. It is like an exclamation
point. Architects always like to have a few of these trees dotted about
the grounds to keep company with tall chimneys and distant church spires.
There is no shade under trees of this form, though miles of them are
planted along roadsides where they stand like tin soldiers, all alike.
The older trees look very ragged, for they are unable to shed their dead
limbs, and as old age comes on they send up suckers from the roots that
form a little forest around the parent tree.
Scattered over fallow fields of worthless ground, the red cedars are
allowed to grow. They are the evergreen counterparts of the slim Lombardy
poplars. Sometimes the red cedar broadens into a pyramid, wide at the
base, but we are all familiar with the green exclamation points, dotted
over the hillsides, wherever birds have dropped the blue berries full of
seeds.
The pointed firs with their horizontal branches becoming longer and
longer towards the ground, are good examples of the pyramid form so
common among evergreens. This is the shape of the spruces, and the pines,
and the hemlocks, until storms have broken their branches, and taken away
the symmetry of the top. The pin oak and the honey locust send out
horizontal branches of graduated lengths from the central shaft,
imitating the evergreens in shape.
The evergreen magnolia of the South has a dome like an old-fashioned
beehive, pyramidal, and regular when it grows in sheltered places. Such a
dome is the hard maple’s in the North.
Some trees branch low, and their short trunks break into great limbs
whose ample spread forms a dome much broader than its height. The white
oak in the North and its evergreen counterpart, the live oak of the
South, illustrate this noble form. Somewhat like them, but with its dome
elevated upon a tall trunk, is the American elm with the fan top. The
lines of the elm branches are all curves from the arching limbs that rise
out of the trunk to the flexible twigs which droop at the extremities of
the branches. The dome of a white oak is made of angular limbs. Even the
twigs are likely to be crooked. No one would confuse the elm with an oak.
Round-headed trees are many. Go from the apple tree in the orchard to the
red and Norway maples along our streets. A great many trees find this
form best adapted to spreading their leaves out towards the sun. Many
oaks and ash trees, the hickories and birches, and the beeches have
widely spreading limbs forming tops that are oblong in shape. There are
trees so irregular in habits of growth that we shall never know them by
their forms alone.
The winter is the best time to study tree shapes, for then the framework
is revealed. The trees to study are those which stand apart from others,
so that they have been able to take their natural shapes. These we shall
find growing on the streets, and in yards, and parks, and in open spaces
in the woods. Where trees crowd each other in growing, their branches
chafe and clash in storms, destroying the buds and leaves, and bruising
the tender bark. Such limbs die of these injuries, and the whole shape of
the tree top is changed by its losses.
[Illustration: Fruiting branch of the cockspur thorn]
[Illustration: Clustered thorns on trunk of honey locust tree; Flowers
and foliage of the black locust]
It is hopeless for lower limbs to live in a dense pine forest. The top
branches form so thick a wall of shade that lower branches die from lack
of sun. It is the same with broad-leaved trees. In any dense woods, the
trees stand bare as telegraph poles, lifting small heads of foliage at
the top, and competing there with their neighbour trees for sun and air.
It is only when set apart from other trees that a trunk can keep its
lower branches hale and strong as those at the top.
The weeping habit gives us some strange tree forms. The Camperdown elm
forms a shady summer-house on many a lawn by arching limbs which droop to
the ground on all sides of the main trunk. The weeping mulberry has the
same habit. Weeping birches and willows have such light foliage, and such
fine, flexible twigs, that they look like fountains of green as they
stand among the other trees.
All weeping trees are made by grafting in the nursery rows. They are not
grown from seeds, and it is not true that they “weep” because of being
planted up-side-down! This preposterous notion is not uncommon.