HOW PLANTS FEED AND GROW 31 



carbohydrates, such as the sugars, starches, fats, and oils, and 

 woody fiber, or cellulose, are made only by green plants, and by 

 them only in the green parts, that is, principally, in the leaves. 

 Under the influence of the sun's rays upon the green mate- 

 rial (chlorophyll] the carbon dioxide of the air, which enters the 

 leaves through the stomata, is broken up into its constituents, 

 carbon and oxygen. These are then combined with the elements 



FIG. 1 6. Seed formation and food storage in corn 



Pollen from the tassel (at right) falls upon the silk of the ear (at left), and fertilization 

 results. As the ovules ripen into grains they are stored with food material 



which compose water hydrogen and oxygen. Although the 

 details of this process are not yet fully known, it is known 

 that by successive steps the elements composing water and car- 

 bon dioxide hydrogen, oxygen, and carbon are built into 

 grape sugar, or glucose, and later into starch ; it is also known 

 that much oxygen is released into the air by the work of chloro- 

 phyll. Sugar is soluble in the cell sap and is easily transported 

 through the plant to any place where it is needed. The sugar 

 which a corn plant makes can easily be found in the stalk at 

 flowering time. Indeed, if the ears be stripped off, so that the 



