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CONTRIBUTIONS TO THE BIOLOGY OF RHIZOBIA. 



I. RHIZOBIUM MUTABILE IN ARTIFICIAL CULTURE MEDIA. 



Albert Schneider. 



(with plate i) 



Recently I began some further work on the biology of 

 rhizobia. The investigations carried on at the Illinois Experi- 

 ment Station at Champaign in 1893 were terminated before any 

 satisfactory results were reached, and it is only recently that an 

 opportunity has again presented itself to further pursue the 

 investierations. 



The review of recent work done in the study of rhizobia will 

 ^ be given in the second paper. A fairly complete list of refer- 



ences up to and including the year 1897 ^^'^^^ t)e found in the 

 tnesota Botanical Studies of September 27, 1894, to which a 



Ml 



supplement was added in the Studies of May 29, 1897. 



Since 1886 numerous investigators, especially those of 

 Germany and France, have attempted to make pure cultures of 

 rhizobia, and some of these have stated repeatedly that cultures 

 were obtained, but not a single investigator has thus far 

 given detailed information regarding them. Other investi- 

 gators, again, declared that rhizobia were incapable of being 

 grown in artificial media ; that they were, indeed, merely 

 plasmic by-products, to which the name Bakteroiden was given 

 by Frank and other German investigators. Another source of 

 confusion and difficulty was the fact that most investigators 

 recognized only one form (or species) of rhizobium, namely, the 

 Rhizobium legtiminosartim of Frank. Without entering again 

 into a discussion of the probable number of species, I shall out- 

 line briefl3^ ^^e present preliminary investigations. 



I have made repeated attempts to obtain pure cultures of the 

 rhizobia found in the root tubercles of Melilotus alba, but with 

 either wholly negative results or only a very evanescent partial 



success. So frequent were my total failures that I became 



1902! 



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