328 



GENERAL SCIENCE 



a c c 



FIG. 289. A Section of a 



cells, which by changing their shape control the amount 

 of air breathed in by the plant and also the amount of 

 evaporation of water from the leaf (Figure 289) . 



Starch Making by Leaves. The leaves also serve 



as a factory in which starch and sugar are manufactured. 



a To do this the leaves combine water 



- -+- and carbon dioxide. Since there is 



more oxygen in the air than is needed 

 to produce the carbohydrates, starch 

 and sugar, the excess oxygen is 

 breathed out by the leaves. Thus 

 plants tend to purify the air by 

 exchanging oxygen for the carbon 

 dioxide in it. The manufacture of 

 starch and sugar in the leaf is car- 

 ried on by the chlorophyll bodies 

 Leaf. within the leaves under the influ- 



a, epidermis; b, cells; ence of the energy of sunlight. The 

 sunlight and the chlorophyll bodies 

 are the agents in the production of these carbohydrates, 

 and the water and carbon dioxide are the raw materials 

 from which they are made. 



Plants that have been grown in the dark, and plants 

 that lack green coloring matter (chlorophyll) contain 

 no starch or sugar. 



Digestion in Plants. Food products in plants, as in 

 animals, may require changes before they can be used as 

 foods. Starch is a food for plants, but it is quite insoluble 

 in water and must be digested before it can be used. 

 This is accomplished by changing the starch to sugar, 

 which is dissolved by the water and carried to the differ- 

 ent parts of the plant. 

 Flowerless Plants. The flowering plants are the 



