I 



¥ 



¥ 



V 



1902] CONTRIBUTIONS TO THE BIOLOGY OF RHIZOBIA 1 1 1 



making the inoculations I noticed in several of the streaks a 

 very slight, translucent, glistening growth, which at once 

 reminded me of similar prrowths observed in mv former investi- 



gations. Upon microscopic examination I found numerous 

 organisms, some simple and irregular in form, some Y-shaped, 

 some twice and three times forked, resembling the rhizobium of 

 the sweet clover to which I gave the name Rhizobium fnntabile 

 m 1892. Of these few small growths I made a number of test- 

 tube cultures. These cultures developed very slowly, but 

 steadily, producing (upon agar media) a transparent, glistening, 

 slightly elevated, smooth-margined growth of about the tenacity 

 (not stringy) and consistency of syrup. There was no color, 



^ odor, or gas formation noticeable. Repeated microscopic 



examinations showed these cultures to consist of organisms 

 having the morphological characteristics of R. jmitabilc of sweet 

 clover. These morphological characteristics, combined with the 

 very peculiar development of the cultures, led me to assume 

 that I had at last succeeded in obtaining pure cultures of R, 

 mittabile. H. B. Carey, working in the same laboratory, suc- 

 ceeded in obtaining numerous similar cultures from M. alba 

 tubercles by the fractional culture method. The evidence, 

 though requiring further proof, is sufficient to justify this report. 

 Inoculation experiments on M, alba growing in carefully steril- 

 ized soil are now in progress, which will be reported upon in the 

 second paper. 



^licroscopic examination of pure cultures showed the rhizobia 

 in various stages of septation, budding, and branching. The 

 organisms are absolutely non-motile, showing more irregularity in 

 form, size, and branching than in their normal state within the 



^ tubercle. They are embedded in a considerable quantity of 



mucilaginous substance, which does not, however, form a dis- 

 tmctly circumscribed layer about the cell wall. Naturally the 



\ study of the mode of multiplication is a comparatively easy task 



with pure cultures. It multiplies by bi-septation, multi-septation, 

 and by budding and subsequent septation. In comparatively 

 rare instances there is evidence of budding resembling that of 



