"You must remember," said Fred, "that the foot- stalk, ribs, and veins all form channels for the upward flow of the earth-food. And now I want you to think of something else. What becomes of the carbonic acid gas which is always being formed, in the air?""Oh, I know," said Norah. "The plants take it in. Then I suppose it is the carbonic acid gas that is absorbed by the breathing pores of the leaves.""Yes, it is," said Fred. "The breathing pores absorb carbonic acid gas from the air. In the leaves this gas is broken up. The plant takes for its own use a part of it, which we call carbon or charcoal,and breathes out the rest to the air again. The carbon is absorbed by the sap, which now becomes air-food as well as earth-food, and is carried away into all parts of the plant."SUMMARY
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