16 Martin J. Prucha 



A pure culture of the organism was isolated from a nodule found on one 

 of the plants grown under sterile conditions. This organism was again 

 tested as to its ability to produce nodules on Canada field peas. Fifteen 

 Canada field pea plants were grown under sterile conditions again, in a 

 similar manner to that described above. Five were inoculated with this 

 organism, five were inoculated with the original organism, and five were 

 left as controls. Agam all the plants inoculated with both the cultures 

 developed nodules on their roots, while the controls had none. The 

 organism that was isolated on October 10, 1910, therefore, was the causal 

 organism of nodules on Canada field pea plants, and as far as could be 

 determined by laboratory methods it was also a pure culture. 



The two cultures of the organism — the one isolated originally, and 

 the other isolated from a nodule of a plant grown under sterile coiiditions 

 — were studied in the laboratory with respect to their morphology and 

 their physiological activities. An exhaustive study of this phase was not 

 undertaken, the study being carried only far enough to show whether 

 the two cultures were the same organism. The study consisted in propa- 

 gating the two cultures on various media and in comparing and describing 

 their cultural and biochemical features. The descriptions were recorded 

 on the Descriptive Chart adopted for such use by the Society of American 

 Bacteriologists (1907). 



Morphology oj the organism 



Bacillus radicicola of Canada field pea produces no spores when prop- 

 agated on the artificial media in the laboratory. In a young culture on 

 artificial media, the organism is in the form of small rods about one micron 

 long. In this form it is able to multiply by fission, like other bacteria. 

 Under certain conditions — for example, with the addition of certain 

 nutrients, such as sugar, to the media — some of these small rods develop 

 into large cells, which are generally called bacteroids. Some of the bac- 

 teroids assume the characteristic X and Y forms, the same as are found 

 in the nodules. The development of the bacteroids seems to be largely 

 a matter of nutrition, and the bacteroids are not a degenerate form, but 

 a normal form, of the organism. 



In a culture twenty-four hours old on an agar slope the organism is 

 very motile. As the agar-slope culture gets older, fewer and fewer of the 

 organisms show motility, until in a culture about two weeks old no motility 



