CELLULOSE AS A SOUECE OF ENEEGY FOE NITEOGEN FIXATION. 29 



tion gcive 0.7 to 2.84 milligrams to each gram of dextrose used. It 

 would app?ar. therefore, that comparatively large quantities of pep- 

 tone liad a stimulating effect on the nitrogen-fixing properties of 

 Clostridium pasteurianum and Bacillus amylohacter. 



In 1909 Latham secured unusually high fixation wdth Asperc/illus 

 niger in nutrient solutions containing from 115.4 to 156.3 milligrams 

 of nitrogen as ammonium nitrate for each 50 cubic centimeters of 

 solution; however, when the nitrogen added amounted to 160.3 

 milligrams to each 50 cubic centimeters of solution there was a loss 

 of nitrogen. Latham concludes that the critical point with regard 

 to the nitrogen supply for Aspergillus niger is slightly below 160.3 

 milligrams to 50 cubic centimeters of solution. The percentage of 

 nitrogen added to these solutions is much greater than the total 

 percentage found in soils or in most plant tissues, and yet the nitrogen 

 gains seciu'ed are very liigh for this organism. 



Stahel in 1911 in studying the nitrogen-fixing power of various 

 molds in nitrogen-free and nitrogen-containing solutions secured a 

 decided stimulating effect by the addition of nitrogen as potassium 

 nitrate in quantities from 0.002 to 0.016 per cent. 



After a somewhat careful review of the literature bearing upon the 

 effect of combined nitrogen on the nitrogen-fixing power of micro- 

 organisms it seems to the writer that there are not sufficient data to 

 show that the presence of considerable quantities of combined nitro- 

 gen in the culture media reduces or destroys the nitrogen-fixing 

 properties of organisms which show a pronounced nitrogen-fixing 

 power in nitrogen-free solutions. On the contrary, the data ob- 

 tamable seem to indicate that the nitrogen-fixing power of some 

 organisms may be greatly stimulated by the addition of nitrogen 

 to the culture medium. 



EFFECT OF AMMONIUM SULPHATE UPON THE NITROGEN-FIXING 

 POWER OF AZOTOBACTER CHROOCOCCUM AND AZOTOBACTER 

 BEIJERiNCKII IN NUTRIENT SOLUTIONS. 



The nutrient solution employed in this experiment was prepared 

 according to the formula recommended by Ash by, except that 15 

 grams of mannite to the liter were added. After a thorough mixing 

 the solution was divided into two equal parts; one portion then re- 

 ceived an addition of 1 gram of ammonium sulphate to the liter. 

 The solutions were distributed in 1-liter Erlenmeyer flasks, 200 cubic 

 centimeters being placed in each flask. After sterilization, two flasks 

 from each lot of solution were reserved for initial nitrogen and the 

 remaining solutions inoculated witli Azotohncter chroococcum or A. hei- 

 jerincMi and incubated for 18 days at 30° C. The results are sho\vn 

 m Tuble I.^ 



1 The nitrogen determinations included in tliis and in the following tables were made by Dr. T. C. Trescot, 

 of the Bureau of Chemistry, U. S. Department of Agriculture. 

 £Cir. 131] 



