BACTERIA FOR LEGUMES 137 



inhabit alfalfa, melilotus and the bur clovers. It seems 

 necessary to have separate inoculation for cowpeas and 

 soybeans, while sainfoin, which has nearly always been a 

 failure in America, is probably a failure in most instances 

 through lack of inoculation. Red clover, alsike clover 

 and little white clover seem to take the same bacteria, 

 while it is doubtful whether crimson clover can get along 

 without its specific bacteria. 



One can tell "how it is done" as easily as one can de- 

 fine the nature of electricity. What we can see is that 

 the bacteria attack the rootlets which very graciously 

 build out fleshy coverings for them, "nodules" or "tu- 

 bercles." These nodules vary in size from that of a very 

 small seed to the size of a pea or larger. The nodules, 

 are full of nitrogen and inhabited by millions of bacteria. 

 These bacteria are continually reproducing, growing, dy- 

 ing, giving up their nitrogen to the soil and plants. The 

 bacteria obtain their nitrogen from the air that enters all 

 good, dry, pervious soils. When you stop to think of it, 

 nearly all leguminous plants thrive best in dry soils that 

 the air easily can enter. 



How the bacteria get from one part of the soil to an- 

 other, how natural inoculation takes place, we do not 

 know. Probably it is done mainly by the washing of 

 soils and perhaps sometimes by the wind. Sometimes 

 the bacteria do not come until they are artificially intro- 

 duced by man. In some neighborhoods the bacteria of 

 alfalfa are found everywhere and no inoculating is need- 

 ed; in other neighborhoods, alfalfa seeding is a failure 

 unless the proper bacteria are introduced. 



