RELATION OF PLANTS TO ENVIRONMENT 11 



instance of this fact is that of the farmer fertilizing his fields 

 with fertilizers composed of the remains of plants and the 

 excrements of animals. 



We have now completed the general survey of the relation 

 of green and colorless plants to that part of nature which 



INCOME OUTGO 



I. FROM SUN 



ENI 



GREEN PLANT 



FIG. 4. Organic food cycle 



What three classes of organisms are represented as concerned with the construction 



and use of foods in the world ? What part does each play in the maintenance and 



consumption of its food supply ? What distinctive relation has the green plant to the 



maintenance of the world's food supply? 



constitutes their environment. The details of the picture will 

 be filled in as we proceed in later chapters with the structure 

 and work of plants. 



Plants and the environment of animals. We are not accus- 

 tomed to think of the earth as it would be without the plant 

 life which both clothes and beautifies it. The protective, en- 

 vironmental function of plants is perfectly obvious, however, 

 without lengthy comment or discussion. The great forests form 

 a necessary environment for hundreds of species of animals, 

 ranging from the larger forms, which make their homes in 



