relationship to each other. Closer observation, however, will reveal
that the forest consists of a distinct group of trees, sufficiently
dense to form an unbroken canopy of tops, and that, where trees grow
so closely together, they become very interdependent. It is this
interdependence that makes the forest different from a mere group of
trees in a park or on a lawn. In this composite character, the
forest enriches its own soil from year to year, changes the climate
within its own bounds, controls the streams along its borders and
supports a multitude of animals and plants peculiar to itself. This
communal relationship in the life history of the forest furnishes a
most interesting story of struggle and mutual aid. Different trees
have different requirements with regard to water, food and light.
Some need more water and food than others, some will not endure much
shade, and others will grow in the deepest shade. In the open, a
tree, if once established, can meet its needs quite readily and,
though it has to ward off a number of enemies, insects, disease and
windstorm--its struggle for existence is comparatively easy. In the
forest, the conditions are different. Here, the tree-enemies have to
be battled with, just as in the open, and in addition, instead of
there being only a few trees on a plot of ground, there are
thousands growing on the same area, all demanding the same things
out of a limited supply. The struggle for existence, therefore,
becomes keen, many falling behind and but few surviving.

[Illustration: FIG. 124.--Measuring the Diameter of a Tree and Counting
its Annual Rings.]

This struggle begins with the seed. At first there are thousands of
seeds cast upon a given area by the neighboring trees or by the
birds and the winds. Of these, only a few germinate; animals feed on