140 SOILS 



These phenomena, the Y and T forms and the pouch-like 

 threads, have been puzzles to bacteriologists, for they 

 are not characteristic of any other bacteria known. It 

 has been doubted whether the organizations should be 

 called bacteria." 



But whether these are bacteria or not, the fact remains 

 that they are responsible for nitrogen fixation, and 

 hence, they are soil builders and world benefactors. 



Suggested ways in which fixation is done. We are 

 certain of this fact : nitrogen is fixed in the soil in a form 

 in which it is assimilable by plants and especially usable 

 by the legumes. We are not certain, on the other hand, 

 of the manner in which this fact is accomplished. 



Four theories have been suggested, as follows : 



1. The bacteria (bacillus radicicola) fix the nitrogen. 



2. Legumes fix the nitrogen, the bacteria being the 

 stimulus of the act. 



3. A combined act of the legume plant and tubercle 

 bacteria in assimilating nitrogen already fixed in the soil 

 by other bacteria but unassimilable until legume and 

 tubercle bacteria act on it together. 



4. Symbiosis : A combined act of the legume plant and 

 tubercle bacteria in gathering nitrogen from the air. 



In case of either theory, the legume plant is inseparably 

 associated with bacteria. The question arises : How is 

 the work done? 



The first theory allows one conclusion : bacteria do 

 the work entirely of themselves. The only value of the 

 legume is its offering a suitable dwelling spot for the 

 workers. While some evidence points to this theory, but 

 few accept it as an explanation of nitrogen fixation. 



The second theory, that the legumes fix the nitrogen 

 after being stimulated by the bacteria associated with 

 them, is not generally held, although its advocates boldly 



