FOOD CYCLES AND MICROBES 123 



Plants feed on the water in the air. They ab- 

 sorb it largely by their roots, stems, branches and 

 leaves. They could not live and grow without it. 

 Animals living on plants appropriate the same 

 water and much more. When plants and animals 

 die and are dissolved, the water returns again into 

 the air, ready for another round in the water cycle. 



Of course there is another larger water cycle. 

 By evaporation water is drawn up by the sun into 

 the air from all the seas, and falls on the land as 

 rain, dew and snow, and returns again in rivers 

 to the seas, ready for another round in the greater 

 water cycle. 



Through the agency of their leaves, plants take 

 carbon from the air, under the influence of the 

 sun picking the carbon atoms from the molecules 

 of carbon dioxide, and appropriate it as food. 

 Animals live on plants and incorporate the same 

 food into their own systems. When both plants 

 and animals die, during the dissolution of their 

 bodies the carbon therein unites with oxygen and 

 returns again as carbon dioxide into the air, ready 

 for another round in the carbon cycle of food. 



Great quantities of oxygen are taken from the 

 air, day by day, moment by moment, to feed hun- 

 gry vegetable mouths. Every animal that breathes, 

 by virtue of lungs, spiracula, or gills, breathes oxy- 

 gen. Every fire that burns, burns oxygen. Every 

 decay of animal or vegetable substance is a slow 

 fire consuming oxygen. It is estimated that for 

 these three purposes not less than 7,000,000 tons 



