THE STRUGGLE TO LIVE
Every plant and animal is _exposed to unfavorable conditions_. It is
obliged to contend with these conditions in order to live.
[Illustration: FIG. 3.--A BATTLE FOR LIFE.]
No two plants or parts of plants are identically exposed to the
conditions in which they live. The large branches in Fig. 1 probably
had more room and a better exposure to light than the smaller ones.
Probably no two of the leaves in Fig. 2 are equally exposed to light,
or enjoy identical advantages in relation to the food that they receive
from the tree.
Examine any tree to determine under what advantages or disadvantages
any of the limbs may live. Examine similarly the different plants in
a garden row (Fig. 3); or the different bushes in a thicket; or the
different trees in a wood.
The plant meets its conditions by _succumbing to them_ (that is, by
dying), or by _adapting itself to them_.
The tree _meets the cold_ by ceasing its active growth, hardening its
tissues, dropping its leaves. Many herbaceous or soft-stemmed plants
meet the cold by dying to the ground and withdrawing all life into the
root parts. Some plants meet the cold by dying outright and providing
abundance of seeds to perpetuate the kind next season.
[Illustration: FIG. 4.--THE REACH FOR LIGHT OF A TREE ON THE EDGE OF A
WOOD.]
Plants _adapt themselves to light_ by growing toward it (Fig. 4); or by
hanging their leaves in such position that they catch the light; or,
in less sunny places, by expanding their leaf surface, or by greatly
lengthening their stems so as to overtop their fellows, as do trees and
vines.
The adaptations of plants will afford a fertile field of study as we
proceed.
=Struggle for existence= and =adaptation to conditions= are among the
most significant facts in nature.
The sum of all the conditions in which a plant or an animal is placed
is called its =environment=, that is, its surroundings. The environment
comprises the conditions of climate, soil, moisture, exposure to light,
relation to food supply, contention with other plants or animals. _The
organism adapts itself to its environment, or else it weakens or dies._
Every weak branch or plant has undergone some hardship that it was not
wholly able to withstand.
SUGGESTIONS.--The pupil should study any plant, or branch of a plant,
with reference to the position or condition under which it grows, and
compare one plant or branch with another. With animals, it is common
knowledge that every animal is alert to avoid or to escape danger,
or to protect itself. =2.= It is well to begin with a branch of a
tree, as in Fig. 1. Note that no two parts are alike (Chap. I). Note
that some are large and strong and that these stand farthest towards
light and room. Some are very small and weak, barely able to live
under the competition. Some have died. The pupil can easily determine
which ones of the dead branches perished first. He should take note
of the position or place of the branch on the tree, and determine
whether the greater part of the dead twigs are toward the center of
the tree top or toward the outside of it. Determine whether accident
has overtaken any of the parts. =3.= Let the pupil examine the top of
any thick old apple tree, to see whether there is any struggle for
existence and whether any limbs have perished. =4.= If the pupil has
access to a forest, let him determine why there are no branches on
the trunks of the old trees. Examine a tree of the same kind growing
in an open field. =5.= A row of lettuce or other plants sown thick
will soon show the competition between plants. Any fence row or weedy
place will also show it. Why does the farmer destroy the weeds among
the corn or potatoes? How does the florist reduce competition to its
lowest terms? what is the result?