CHAPTER VI 



HOW THE LEAF GETS FOOD FROM THE AIR 



What is the work of the leaf ? We often hear that 

 the plant gets all its food from the soil. This is not so. 

 Some of its food comes from the soil, but it gets most of 

 its food from the air through the leaves. The first 



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thing it does with the air food is to make starch from 

 it by the aid of sunlight. And so we find starch in every 

 active leaf. All the substance of the plant is made 

 from the starch by the soil food which comes up from 

 the roots. So the first work of the leaf is to make 

 starch from the air food. 



How the leaf takes up air food. The root must 

 have as great a surface as it can to take up the 

 little water the soil contains. The leaf must spread 

 out as great a surface as it can to take up the little 

 food the air contains. The leaves of a large tree 

 may have several hundred square feet of leaf sur- 

 face, but the real absorbing surface is inside the leaf, 

 and is many times greater, just as the absorbing sur- 

 face of our own lungs is greater than the outer surface 

 of our bodies. The cells or chambers of which it is 



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