Studies of Bacillus Radicicola of Canada Field Pea 33 



such is the case, and also to determine the media most favorable for 

 maintaining the vitality of the organism, the following experiments were 

 made. 



The term virulence has been used by previous investigators to mean 

 the ability of the organism to penetrate the root and produce nodules. 

 Since the term virulence in this connection, as also suggested by Edwards 

 (in Marshall's Microbiologic), does not correctly apply to the legume 

 bacteria, the term injecthig power will be used throughout this paper. 



Bej^erinck (1890) was the first to isolate a pure culture of an organism 

 from a nodule. Prazmowski (1890), Frank (1889), and Nobbe and others 

 (1891), stimulated by Beyerinck's success, were also able to obtain pure 

 cultures from the nodules of various legumes, and to produce nodules by 

 inoculating the plants with the pure cultures. The experiments on the 

 inoculation of legumes by pure cultures at once raised a question as to 

 the classification of the nodule-forming organism, which question is in- 

 timately connected with the subject of the infecting power of the organism 

 and the resistance of the plants. Do all the different organisms from 

 the various species of legumes belong to several species, or do they belong 

 only to one species but to several races or varieties? Can the organism 

 from one species of legumes cause nodules on a different species of legumes? 

 Is the relation between the legume and the organism a case of symbiosis 

 or a case of parasitism? Does the organism have the biological or physio- 

 logical character called virulence as understood by pathologists, and can 

 this be altered or destroyed without injuring or destroying the other 

 physiological activities? Do the host plants have a resistance in a patho- 

 logical sense, and can this resistance be altered by the environmental 

 factors without altering the morphology, the structure of the tissues, 

 and the physiological activities of the plants? Is the resistance against 

 the entrance of the organism into the root tissues different from the 

 resistance against the development of the organism inside the root tissues? 

 These and similar questions formed the foundation of the numerous 

 investigations that were undertaken subsequently to the isolation of the 

 pure culture of the nodule-forming organism, and nodule production by 

 pure cultures. 



Even before the isolation of the nodule-forming organism by Beyermck, 

 it was observed by Hellriegel (1886) that when peas, vetch, beans, clover, 

 serradella, and lupines were inoculated with an infusion from the same 



