CHAPTER XXIX 



MICROBES AS ENRICHERS OF THE SOIL 



WHATEVER other agencies are used in keeping up 

 the fertility of the soil, an all important part ia 

 played by microbes. 



First, the ash of all plants is mineral. The 

 bones, too, of all animals are mostly mineral. 

 Both plants and animals, therefore, require min- 

 eral substances in their food. The animal derives 

 this substance from the plant, the plant from the 

 soil, and the soil from the rock. 



But before the soil can furnish this substance 

 in a form which can be appropriated as food by the 

 plant, the rock must be crumbled and ground to 

 powder. The molecules of the powder, too, must 

 be separated into their atoms and the atoms re- 

 combined into other molecules forming the various 

 mineral salts. The crumbling and powdering are 

 done by chemical and physical forces, air and 

 sunshine, moisture and drouths, heat and cold, 

 torrential stream and cataract, and the grinding 

 power of the iceberg. But the breaking up of the 

 molecules and the forming of new ones are affected, 

 in part at least, by microbes. 



Second, all other food furnished plant life by 



in 



