e food
from the air. The plant can become and remain green only under the
influence of sunlight. So finally the plant owes its life to the power
of the sun, just as in one way or another we all do. Plants in a dark
place soon lose their green color, grow pale and sickly, and finally
die. All green leaves and the young green twigs are able to take food
from the air. The food they thus take is carbon dioxide, the very thing
both plants and animals breathe out as a waste, and whose presence in
large quantities makes air unfit to breathe. But the plant must have the
carbon dioxide and can get it only from the air, so it is constantly
withdrawing this harmful substance from the air and converting it into
plant tissue. It consumes only part of the carbon dioxide, however, for
the oxygen that is tied up in the carbon dioxide is set free and given
back to the air, only the carbon being retained. So the plant is
continually taking in the destructive carbon dioxide and giving out the
wholesome oxygen, thus keeping the air pure and fit for us to breathe.
In short, the plant eats with its roots and with its leaves. With its
roots it eats certain things it finds in the earth, and with its leaves
and other green parts it eats the suffocating gas we breathe into the
air.

This important function of the plant, in supplying the oxygen we need
and in destroying the harmful carbon dioxide, can be illustrated in many
graphic ways. We depend upon the plants for our very existence in this
respect: they stand between us and destruction from excessive
accumulations of carbon dioxide. On the other hand, the carbon dioxide
is so important to the plant that it could not exist without it. All the
carbon it gets is obtained from this source. Wood is largely carbon; a
charred stick which retains its full size and shape is almost pure
carbon. Thus the breath of our bodies is converted by the plant into the
wood from which we construct our houses, furniture, etc. In a certain
sense the chair we sit upon is made of the breath of our bodies. Besides
these debts to the plant, we finally owe to it the food we consume,
which comes from the plant, even meat being but vegetable matter one
step removed. The plant changes the chemicals which the animal cannot
use in their crude form, into plant substances which animals can use.
Thus the vegetable and animal kingdoms are mutually dependent upon each
other. Neither could exist, at least in its present condition,