Studies of Bacillus Radicicola of Canada Field Pea 77 



tion, and the products of their metabohc activities, may exercise an in- 

 jurious influence on the nodule organisms and thus prevent them from 

 multiphcation and distribution through the soil. 



The influence of artificial media on the power of Bacillus radicicola to 

 cause nodules is of considerable importance, in view of the fact that 

 inoculation for leguminous crops with pure cultures is extensively prac- 

 ticed and the pure cultures have to be propagated on some media. Frank 

 (1899), m commentmg on the low efficiency of nitragin, suggested that 

 probably the medium (gelatm) on which the cultures were propagated 

 and kept was not favorable for the organisms, and that this might be the 

 cause of the low efficiency of nitragin. Hiltner (1900) finally substituted 

 liquid media for the gelatin, and was able to obtain better results from 

 the legume inoculation. Siichting (1904) found that not onl}' the gelatin 

 media are injurious to the bacteria — a point shoT\Ti by Hiltner — but 

 the agar media also may be unfavorable. Moore (1905) made the ob- 

 servation that the nodule-forming bacteria increase most rapidly on a 

 medium rich in nitrogen, but that the resulting growth is usually very 

 much reduced in infecting power. Lewis and Nicholson (1905), on the 

 other hand, state that the presence or absence of nitrogen in the culture 

 media is not the determining factor in maintaining the activitj^ of the 

 germ. 



A reasonable conclusion from the investigations mentioned above 

 seems to be that some artificial media are more favorable than others 

 for the propagation of B. radicicola, and that the amount of growth is 

 not always directly proportional to the nodule-producing efficiency of 

 the organism. With this conclusion the ex|3eriments in Part III are in 

 accord. In addition to this, the experiments point to the conclusion 

 that B. radicicola of Canada field pea does not possess " virulence " in 

 a pathological meaning of the word. The ability to cause nodules is so 

 closely bound up with the general vitality of the bacteria that our means 

 and methods cannot detect any variations, if such there are, in their 

 nodule-producing ability. The writer's opinion is that every living 

 nodule-producing organism in a vigorous condition, will, if given a chance, 

 cause nodule development no matter on what kind of media it has been 

 propagated. The propagation of the organisms on different media does 

 not measurably affect their nodule-producing efficiency. The organisms 

 die sooner on some media than on others, and the loss of the nodule- 



