THE NEW EVOLUTION 



inorganic substances. As they can do this only with 

 the aid of sunlight, the animal life of the entire world 

 is supported by plants growing on the surface of the 

 exposed land areas, or attached to the bottom, freely 

 floating, or suspended in water of not more than six 

 hundred feet in depth. So the sun-lit surface of the 

 land and the sun-lit surface of the sea provide the basic 

 food for all forms of life from the highest mountain 

 tops to the depths of the deepest caves and down to 

 the great abysses in the sea. 



The plants containing chlorophyll or a comparable 

 substance get the materials necessary for their growth 

 from substances dissolved in the water in the soil, or 

 in the water of ponds, lakes, rivers, or the sea, and 

 from gases in the air or dissolved in water. 



Just as water is essential to the life of every plant, so 

 also is it essential to the life of every animal. Since 

 foodstuffs are available for use by animals and plants 

 only when they are accompanied by an adequate sup- 

 ply of water, the very unequal distribution of this 

 liquid is the chief controlling factor affecting all life 

 on land. 



Some regions are extremely wet, while others are 

 extremely dry; in others the supply of water is very 

 variable at different seasons of the year, or the hu- 

 midity may vary very greatly between the night and 

 day. In the north for a greater or lesser portion of 

 the year the water becomes ice — in other words it 

 changes over into a form in which it is not avail- 

 able for use by the very great majority of plants and 

 animals. 



[44] 



