gs in such a way as to catch the most sunlight. The leaves
take up the carbonic acid gas from the air, decompose it under the
influence of light and combine it with the minerals and water
brought up by the roots from the soil. The resulting chemical
combinations are the sugars and starches used by the cambium layer
in building up the body of the tree. A green pigment, _chlorophyll_,
in the leaf is the medium by which, with the aid of sunlight, the
sugars are manufactured.

[Illustration: FIG. 88.--Roots of a Hemlock Tree in their Search for
Water.]

The chlorophyll gives the leaf its green color, and this explains
why a tree pales when it is in a dying condition or when its life
processes are interfered with. The other colors of the leaf--the
reds, browns and yellows of the fall or spring--are due to other
pigments. These are angular crystals of different hues, which at
certain times of the year become more conspicuous than at others, a
phenomenon which explains the variation in the colors of the leaves
during the different seasons.

It is evident that a tree is greatly dependent upon its leaves for
the manufacture of food and one can, therefore, readily see why it
is important to prevent destruction of the leaves by insects or
through over-trimming.

The root: The root develops in much the same manner as the crown. Its
depth and spread will vary with the species but will also depend
somewhat upon the condition of the soil around it. A deep or a dry
soil will tend to develop a deep root, while a shallow or moist soil
will produce a shallow root, Fig. 88.

The numerous fine hairs which cover the roots serve the purpose of
taking up food and water from the soil, while the heavy roots help
to support the tree. The root-hairs are extremely tender, are easily
dried out when exposed to the sun and wind, and are apt to become
overheated when permitted to remain tightly packed for any length of
time. These considerations are of practical importance in the
planting of trees and in the application of fertilizers. It is these
fine rootlets far away from the trunk of the tree that have to be
fed, and all fertilizers must, therefore, be applied at points some
distance from the trunk and not close to it, where merely the large,
supporting roots are located. In the cultivation of trees the same