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

growing plants.



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.





=EXERCISE=



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

carbon?





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