286 



DISTRIBUTION OF BACTERIA 



legumes (Fig. 58). It 

 is now known that the 

 nitrogen fixation is 

 brought about by the 

 bacteria which produce 

 these nodules. The 

 knowledge which has 

 been gained in recent 

 years has opened up a 

 number of problems, 

 the solution of which 

 would be of the great- 



V^fiHRP^^'- est im p rtance to a & ri ~ 



'^-'\ i^V culture. Some ' soils 



^/-Jtem inlwlk-Qh. . ,*N 



seem to lack the proper 



kind of nodule bacteria, 

 and it is necessary that 

 fields where leguminous 

 crops are to be grown, 

 such as clover or alfalfa, 

 should be inoculated 

 with the particular bac- 

 teria (Fig. 59). At- 

 tempts have been made 

 to put up cultures of 

 these bacteria in a form 

 which would make them available for the farmer. Up to the 



FIG. 58. Tubercles on the roots of an old 

 alfalfa plant. After 



