2l6 



Journal of Agricultural Research 



Vol. XII, No. 4 



Table XXVII. — Influence of nitrates on the fixation of nitrogen by Bacillus radicicola, 

 giving the increase in nitrogen — Continued 



EXPERIMENT III 



Culture 



No. 



9 



lO 



II 



12 

 13 

 14 

 15 

 16 



17 

 18 



19 

 20 



Treatment (nitrate in 100 c. c. of medium): 



None 



....do 



....do 



75 mgm. of NO3 as potassium ni- 

 trate 



....do 



....do 



150 mgm. of NO3 as potassium ni- 

 trate 



. . . .do 



....do 



75 mgm. of NO3 as sodium nitrate 



....do 



....do 



150 mgm. of NO3 as sodium nitrate 



....do 



....do 



75 mgm. of NO3 as calcium nitrate 



....do 



....do 



150 mgm. of N03as calcium nitrate 



....do 



....do 



Nitrogen 

 increase. 



Mgm. 



0. 43 



1-53 



1. 17 



I- 45 

 o. 70 

 o. 92 

 o. 62 



It has been shown that, when nitrates are added in varying quantities 

 to sterilized soil, the number of B. radicicola are increased. Provided the 

 the organism can fix a small amount of nitrogen in the absence of nitrate 

 nitrogen, is it not possible that this increase in nitrogen fixation may be 

 due merely to the increase in the number of cells ? It seems that this is 

 true according to the results in Table XXVII. It appears probable that 

 the increase in nitrogen fixed in the presence of nitrates is very likely 

 because of an increase in the number of bacterial cells and not to any 

 physiological change brought about in the organism itself. 



There was a marked increase in bacterial growth on the media con- 

 taining the nitrate compared with the same media free from nitrate. 

 The growth on the latter medium exhibited a normal, whitish watery 

 appearance, characteristic of this organism. On the cultures containing 

 nitrates a much more profuse growth occurred. In many instances a 

 pinkish tint was observed. This pigment production was especially 

 marked in the case of the culture containing the sodium salt. After the 

 first experiment had been completed, it was thought that possibly this 

 pigmentation was due to an impurity in the culture. Therefore the two 

 remaining experiments were made, using a subculture from the original. 



