The leaves are the stomach and lungs of the tree. Their broad
blades are a device to catch the sunlight which is needed in the
process of digesting the food of the tree. The leaves are arranged
on the twigs 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