1902] 



CONTRIBUTIONS TO THE BIOLOGY OF RHIZOBIA 



113 



I > 



f 



t 



4 



especially if the media are not wholly translucent or transparent. 

 In liquid media there is a whitish sediment of rhizobia. There is 

 evidence that grow^ths on solid media become less translucent 

 with age. 



The following is a brief summary of results of the present 



series of experiments : 



1. Rhi zob in f n miitabile C2i\\ be isolated and develops in artifi- 

 cial culture media, forming a translucent, colorless, glistening, 

 semi-liquid growth. 



2. It develops slowly, requiring from four to six days to pro- 

 duce a perceptible growth. 



3. It is essentially aerobic. 



4. It multiplies by biseptation, multiseptation, and a modified 

 form of budding. 



5. It apparently does not develop true spores. 



6. It is devoid of all active motion. 



7. It undergoes great changes of form and size, with age and 

 also in different culture media. See figures. 



8. Refractive bodies (sporoids) occur in the older organisms, 

 and seem to be characteristic of the species. Their origin and 

 function are as yet undetermined. 



9. While of slow growth, it does not seem to be readily 



destroyed. It maybe completely overspread by a foreign germ, 



but as soon as conditions become unfavorable for the latter the 



rhizobium is found to be still active and continues to grow and 

 multiply. 



Northwestern University, 



Chicago. 



EXPLANATION OF PLATE L 



The illustrations are from pen and ink drawings, made on a uniform scale 

 by means of an Abbe camera lucida. The drawing paper was placed on a 

 level with the base of a Leitz instrument. Magnification by means of a B. 



and 



a, Rhizobium miitabile from young root tubercle of Melilotus alba, 



b, R. mntabiU grown in agar beef broth. 

 c> R, muiabile grown in beef broth. 



d, R. mutabile grown in Melilolus alba extract solidified by agar. 





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