28 



CIECULAE NO. 131, BUEEAU OF PLANT INDUSTEY. 



In 1904 Moore in nitrogen-fixation studies with Bacillus radicicola 

 in nutrient solutions secured a fixation of 0.2 to 2.2 milligrams for 

 each 100 cubic centimeters of nitrogen-free solution. When 0.01 

 per cent of ammonium phosphate was added the gains sometimes 

 amounted to 3.1 milligrams to each 100 cubic centimeters of solution. 



Stoklasa in 1908 secured the following results with a solution con- 

 taining 2 per cent of mannite and 0.2 per cent of sodium nitrate 

 held under aerobic conditions at 20° C. and inoculated with Azoto- 

 hacter chroococcum: 



From this experiment Stoklasa concluded that Azotobacter does 

 not assunilate free nitrogen in tlie presence of nitrate. It would seem, 

 however, that there was a slight gahi in nitrogen, as the moculated 

 flasks in every test show an mcrease over the average of the two 

 sterile flasks, though the gains indicated are possibly withm experi- 

 mental error. 



Bacillus radiohacter under similar conditions was found to be a 

 violent denitriiier, liberating in 10 days 76.3 per cent of the nitrate 

 added. 



Bredemann in 1909 in studymg the nitrogen-fixing properties of 

 Clostridium iMsteuricnum and Bacillus amylohacter in peptone-dex- 

 trose solutions secured the following results: 



Organism. 



Quantity 

 of solution 

 employed. 



Clostridium pasteurianum. 



Bacillus amylobacter. 



Cubic centi- 

 meters. 



500 



500 



Peptone 



nitrogi^n 



added. 



MiiU- 



I gramx. 



I 1.600 



{ 7.983 



[ 39.915 



f 1.600 



7. 983 



39.915 



79. ■<25 



Nitrogen 

 gained. 



MiUi- 

 grams. 

 20.656 

 IS. 423 

 17. 031 

 22. 656 

 14. 5S:5 

 16. 871 

 10. 731 



Nitrogen 

 gained 

 per gram 

 of dex- 

 trose em- 

 ployed. 



Mill- 

 grams. 

 2.07 

 1.84 

 1.70 

 6.02 

 3.24 

 4.22 

 2.75 



In another table Bredemann shows the nitrogen-fixing power of 

 Clostridium pasteuricnum in dextrose solutions to which no combined 

 nitrogen was added as varying from 0.8 to 1.3 milligrams to each 

 gram of dextrose consumed; Bacillus amylohacter in a similar solu- 



[Cir. 131] 



