272 



Microbes and You 



Fig. 48. Root nodules on Alsike clover. {From Plant Life. A 

 Textbook of Botany, D. B. Swingle, 2nd ed. Copyright 1942, D. Van 

 Nostrand Company, Inc., New York.) 



The genus Azotohacter includes organisms which live inde- 

 pendently in the soil ( non-symbiotically ) and which can fix atmos- 

 pheric gaseous nitrogen. When the pH falls below about 6.0, 

 however, Azotohacter cease fixing nitrogen until conditions become 

 more favorable for their development. 



The tremendous amount of nitrogen suspended over every acre 

 of ground throughout the world is largely wasted as far as plants 



