CELLULOSE AS A SOURCE OF ENERGY FOR NITROGEN FIXATION. 



31 



NITROGEN FIXATION BY AZOTOBACTER ALONE AND IN ASSOCIA- 

 TION WITH BACILLUS ROSSICA, WITH BOTH DEXTROSE AND 

 CELLULOSE AS A SOURCE OF ENERGY. 



Three nutrient solutions were employed in this experiment 



composition of these solutions is as follows: 



'Potassium phosphate, diliasic 2;ram . . 



Magnesium sulphate do 



Sodium chlorid do . 



Calrium carbonate do 



Dextrose do 



Cellulose do 



Tap water c c. . 



The 



Solution A . 



1 



1 

 1 



2 



10 

 1 

 1, 000 

 Solution B. The same as solution A with the addition of 0.05 per cent of 



ammonium sulphate. 

 Solution C. The same as solution A with the addition of 0.1 per cent of 

 ammonium sulphate. 



The results of this experiment are shown in Table II. 



Table II. — Nitrogen fixation by Azotobacter alone and in association with Bacillus 

 rossica, with both dextrose and cellulose as a source of energy. 



Considering, first, the results of Azotobacter chroococcum alone it is 

 seen that in the nutrient solution to which no combined nitrogen was 

 added this organism gave an average gain of 6.83 milUgrams for each 

 500 cubic centimeters of solution. In solution B the nitrogen gained 

 amounted to but 3.36 milUgrams, which is less than half the gain 

 shown by this organism in solution A; however, since the gain for 

 A. chroococcum in solution C is almost four times as great as in solution 



[Cir. 131] 



