How A Plant Feeds From The Air
If you partly burn a match you will see that it becomes black. This
black substance into which the match changes is called _carbon_. Examine
a fresh stick of charcoal, which is, as you no doubt know, burnt wood.
You see in the charcoal every fiber that you saw in the wood itself.
This means that every part of the plant contains carbon. How important,
then, is this substance to the plant!
You will be surprised to know that the total amount of carbon in plants
comes from the air. All the carbon that a plant gets is taken in by the
leaves of the plant; not a particle is gathered by the roots. A large
tree, weighing perhaps 11,000 pounds, requires in its growth carbon from
16,000,000 cubic yards of air.
Perhaps, after these statements, you may think there is danger that the
carbon of the air may sometime become exhausted. The air of the whole
world contains about 1,760,000,000,000 pounds of carbon. Moreover, this
is continually being added to by our fires and by the breath of animals.
When wood or coal is used for fuel the carbon of the burning substance
is returned to the air in the form of gas. Some large factories burn
great quantities of coal and thus turn much carbon back to the air. A
single factory in Germany is estimated to give back to the air daily
about 5,280,000 pounds of carbon. You see, then, that carbon is
constantly being put back into the air to replace that which is used by
The carbon of the air can be used by none but green plants, and by them
only in the sunlight. We may compare the green coloring matter of the
leaf to a machine, and the sunlight to the power, or energy, which keeps
the machine in motion. By means, then, of sunlight and the green
coloring matter of the leaves, the plant secures carbon. The carbon
passes into the plant and is there made into two foods very necessary to
the plant; namely, starch and sugar.
Sometimes the plant uses the starch and sugar immediately. At other
times it stores both away, as it does in the Irish and the sweet potato
and in beets, cabbage, peas, and beans. These plants are used as food by
man because they contain so much nourishment; that is, starch and sugar
which were stored away by the plant for its own future use.
Examine some charcoal. Can you see the rings of growth? Slightly
char paper, cloth, meat, sugar, starch, etc. What does the turning
black prove? What per cent of these substances do you think is pure
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