278 



TYPICAL FLOWERING PLANTS 



long as there are plenty of green plants, nor, for the 

 same reason, will there ever be enough carbon dioxide 



to poison animals. 



Another vital process 

 which the leaf shows is 

 digestion. It is difficult to 

 explain how the food is di- 

 gested in plants, but scientists 

 have proved satisfactorily 

 that digestion does take place. 

 After the food is digested, 

 it is distributed by circula- 

 tion. In the experiments it 

 was shown that the plant has 

 a vascular system, and that 

 red ink was carried to all 

 parts of the leaf. Evidently, 

 then, a plant has circulation. 

 Food to be used by the 

 plant cells must not only be 

 prepared by digestion and 

 distributed through circula- 

 tion, but each cell must take 

 from the sap what it lacks, 

 and build this food into 

 living plant protoplasm. 

 This process is called as- 

 similation and as a result of 

 it cells grow, divide, and 

 grow to full size again, 

 thereby increasing the size 

 of the plant. 



Summary of the work of the bean leaf : (1) It performs 

 respiration; (2) it performs transpiration ; (3) it manu- 



Figure 270. — Corn Plant. 

 Showing prop roots. 



