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 

 I (C0 2 ) 



Carbon dioxide 

 (C0 2 ) 



Water 



Simple Salts 



Water 

 X(H 2 0) 



Ammonia] 

 (NH? 



Plants 



with chlorophyll 



buildup complex 



organic substances 



They store up 



energy from the sun 



in the process 



and 



form 



Animals 

 and plants without 



chlorophyll 



[which tear down complex 1 Ammonia 

 organic substances I (NH 3 ) 

 and set free energy 

 in the process in 

 form of heat 



I \ 



Energy from sun. Energy 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 

 the plants, part being given 

 the plants from the dead 

 bodies of their own rela 

 tives and part being pre 

 pared from the nitrogen of 



the air through the agency 

 ^-so- 



<%>m 



Animal Life 



soil) 



Nitrites 

 'Nitric Bacteria 



of bacteria, which live 

 upon the roots of certain 

 plants. These bacteria are 

 the only organisms that 

 can take nitrogen from 

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

 plants and animals are limited in the amount available. And the 



Th3 nitrogsn cycle. Trace the nitrogen from 

 its source in the air until it gets back again 

 into the air. 



