162 THE RELATIONS OF PLANTS TO ANIMALS 



directly upon plants, he eats the flesh of plant eating animals, 

 which in turn feed directly upon plants. And so it is the world 

 over; the plants are the food makers and supply the animals. 



Carbon dioxide 

 (C0 2 ) 



Ammonia 



Animals 



and plants without 



chlorophyll 



organic substances 



and set free energy 



in the process in 



form of heat 



Water 

 (H 2 0) 



Ammonia 



Carbon dioxide 

 ( (C0 2 ) 

 Water 



NH.O) 



Plants 



with chlorophyll 



buildup complex 



organic substances 



They store up 



energy from the sun 



in the process 



and 



M 



Energy from sum JSnergy set free 



as heat. 

 The relations between green plants and animals. 



Green plants also give a very considerable amount of oxygen to 

 the atmosphere every day, which the animals may use. 



The Nitrogen Cycle. The animals in their turn supply much 

 of the carbon dioxide that the plant uses in starch making. They 



also supply, some of the 

 nitrogenous matter used by 



X^nimai Life" ' " D^rhp^sing Bacteria. the plants, part being given 



if \ ^5^. the plants from the dead 



" * Free bodies of their own rela- 



tives and part being pre- 

 pared from the nitrogen of 

 the air through the agency 

 of bacteria, which live 

 upon the roots of certain 

 plants. These bacteria are 

 the only organisms that 

 can take nitrogen from 

 the air. Thus, hi spite of all the nitrogen of the atmosphere, 

 plants and annuals are limited hi the amount available. And the 



The nitrogen cycle. Trace the nitrogen from 

 its source in the air until it gets back again 

 into the air. 



