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CIRCULAR NO. 131, BUREAU OF PLANT INDUSTRY. 



A it would seem that the low gains secured in solution B are due to 

 causes other than the addition of 0.05 per cent of ammonium sulphate. 

 The average gain for Azotobacter chroococcum and Bacillus rossica 

 in solution A is but Kttle higher than for Azotobacter alone, and it 

 is believed that the gains in either case came largely, if not entirely, 

 from the dextrose, as B. rossica appeared to be unable to attack the 

 cellulose in this solution, or if the cellulose was attacked the action 

 was so slow that no destruction of the paper could be observed after 

 60 days' incubation. When 0.05 per cent of ammonium sulphate 

 was added to the nutrient solution, a partial destruction of the paper 

 occurred, and it is observed that the nitrogen gains in these solutions 

 are much higher than for those in which no destruction of cellulose 

 could be detected. In solution C, which contained 0.1 per cent of 

 ammonium sulphate, an almost complete destruction of cellulose 

 took place, and it is seen that the nitrogen gains are consistently 

 higher than for either solution A or B. The results secured mth 

 A. heijerinclcii in solution C are not materially different from those 

 secured with A. cliroococcum in this solution. 



Table lIl.^Nitrogert fixation by mixed cultures of Azotobacter and cellulose-destroying. 

 bacteria, with cellulose as a source of energy. 



' The nutrient solution employed in this experiment is the same as solution C, Table II, except that it 

 contained no dextrose. 



[Cir. 131] 



