STUDIES ON AZOTOBACTER CHROOCOCCUM BEIJ. 355 



When this same organism was grown in 100 cc. of a 2 per cent 

 mannitol solution in large Fernbach flasks it fixed the following 

 quantities of nitrogen: 

 Experiment 29-31 . 



Incubation in days 

 8 17 



Check uninoculated (mgm. N2 found) 0.66 0.97 



Inoculated (mgm. N2 found) 3.61 7.47 



Nitrogen fixed (mgm.) 2.95 6.50 



Incubation was done on a klinostat where the solution was 

 kept in continual movement and the layer of solution was never 

 above 0.5 cm. deep. (Bonazzi, 1919.) The organism proved 

 itself to be a nitrogen fixer in the ordinary sense of the term, as 

 it was found capable of utilizing the atmospheric nitrogen. 

 The mannitol in these cultures was not all consumed and it was 

 impossible to study the nitrogen fixation per gram of mannitol 

 consumed. 



From the work of the various investigators quoted in the first 

 part of this memoir, it can be seen that Azotohacter chroococcum 

 maj^ utilize nitrates when grown in their presence. From the 

 data reproduced as table 1 of this contribution Hills draws the 

 following conclusion: ''In regard to the fixation of nitrogen by 

 these strains of Azotobacter it was found that nitrogen was 

 assimilated both in presence and absence of nitrates. It 

 seems evident that sodium and ammonium nitrate in the 

 amounts studied did not prevent the fixation of the atmospheric 

 nitrogen. In fact the presence of these salts seemed to stimulate 

 the process." Again emphasis is placed on this interpretation 

 when the author states: "However in contrast to the work 

 of Stoklasa, both strains of Azotobacter assimilated more atmos- 

 pheric nitrogen in presence than in absence of these salts." 



From table 1 of the present memoir, where Hills' data are 

 recalculated we see that such conclusions are wholly unjustified. 

 Especially is this true when we consider that the analytical 

 method used for the determination of nitrates includes the 

 nitrite nitrogen as well. This speaks against the assumption 

 that "the reduction of nitrates by Azotobacter takes place with 



