BACTERIA AND PLANT FOOD 



279 



bacteria from cowpeas will not develop upon red clover. 

 Thus in a broad way we may say that each distinct legumi- 



Red Clover : Effect of Bacteria 



nous crop has a special form of symbiotic microbe and that, 

 as a rule, these microbes are not interchangeable. 



Decay of Nodules 



Another important fact is that most of these bacteria 

 are unable to live independently in the soil more than five 

 or six years after the crop on which they develop has 

 disappeared. Consequently we cannot expect to find in a 

 given soil the various germs waiting to develop upon any 

 leguminous crop that may be planted. Nor in most cases 

 is it safe to assume that enough of these germs will adhere 



