ZOOGENESIS 



securely locked up in the various minerals of which 

 they are composed, all of the chemical elements which 

 make up the substance of the bodies of the plants and 

 animals. These are released and freed by the destruc- 

 tion of the rocks by air, water, heat and frost. It is 

 the continuous destruction of the rocks and the release 

 thereby of the elements necessary for the formation 

 of their bodies that makes possible the existence both 

 of plants and animals. 



The finely divided particles of rock form soils which 

 cover the mountain sides and the valley floors, and 

 more deeply all of the more level regions of the land. 

 Soils are of many different types, and their ability to 

 support life is dependent upon the temperature, sea- 

 sonal changes and rainfall of the region as well as 

 on the type. 



On the soils grow plants of all descriptions, some- 

 times in small amount as on coarse gravels or on 

 areas of shifting sands, but sometimes in great abun- 

 dance forming extensive forests and broad grass 

 covered plains. 



Obtaining all the materials necessary for their 

 growth from the soil and air and water are the green 

 and comparable plants alone. By means of the green 

 substance, known as chlorophyll, and allied sub- 

 stances, these plants are able to form organic out of 

 inorganic compounds. No form of animal life is able 

 to exist on inorganic foods. 



So all of the animals living on the land depend for 

 their existence on the green plants, either directly or 

 indirectly. Every portion of a green plant — leaves, 



b9] 



