Jan. 28, 191S 



Nitroge n-A ssimilating Bacteria 



221 



mitted, however, that the evidence seems to favor the former contention — 

 namel)?-, that nitrates do not cause the bacteria to lose their nodule- 

 producing power. 



In order to determine whether or not nitrates weaken these organisms, 

 the following experiments were made: Slopes of mannit agar (in test 

 tubes) containing various amountsof sodium and calcium nitrates as indi- 

 cated in Table XXIX were inoculated with B. radicicola. These cul- 

 tures were incubated at 28° C. for one week, when transfers were made 

 to fresh nitrate media and incubated at 28° C. for another week. At 

 the expiration of this time, three 4-day-old seedlings of alfalfa were 

 inoculated with three drops of a suspension of the organism in 5 c. c. 

 of sterile distilled water. The same slope cultures were incubated at 

 28° C. and used for all subsequent inoculations in this experiment. 

 The inoculated seedlings were placed in the greenhouse under cheese- 

 cloth covering. The temperature here during the daytime averaged 

 approximately 30° C. The seedlings were examined for the first appear- 

 ance of nodules and in no case did they appear before 18 to 20 days. 

 A total count of nodules on all plants was made at the end of 45 days. 

 Three subsequent inoculations were made under the same conditions. 

 In this way organisms in contact with nitrate for varying lengths of 

 time could be used. The results of the inoculation experiments are 

 given in Table XXIX. 



Table XXIX. — Influence of nitrates on the infecting power of Bacillus radicicola 



From the results given in Table XXIX it is very evident that under 

 the conditions of the experiment the legume organisms did not lose 

 their power of producing nodules when grown on a medium containing 



