98 



PHYSIOLOGY OF THE FUNGI 



nitrogen but not able to utilize atmospheric nitrogen; (3) fungi able to 

 utilize ammonium and organic nitrogen but unable to utilize atmospheric 

 or nitrate nitrogen; (4) fungi which are able to utilize only organic 

 nitrogen and unable to utilize atmospheric, nitrate, or ammonium nitro- 

 gen. Robbins recognized that the experimental conditions might affect 

 the classification of some fungi. In spite of admitted imperfections the 

 above classification is very useful in preparing media and in discovering 

 the causes of failure of some fungi to grow on certain media. 



Nitrogen -fixing fungi. It has been shown to the satisfaction of all 

 competent investigators that various genera of bacteria {Rhizohium, 

 Azotobacter, Clostridium) contain species which are able to fix nitrogen. 



Table 18. Nitrogen Fixation by Phoma betae and Azotobacter vinlandii 

 (Duggar and Davis, Ann. Missouri Botan Garden 3, 1916.) 



No such agreement exists regarding fungi. Much of the early work on 

 nitrogen fixation by fungi was done without using proper precautions. 

 However, in several instances the experimental methods appear to be 

 beyond reproach. Duggar and Davis (1916) cultured Phoma betae and 

 Aspergillus niger in Kjeldahl flasks and determined the nitrogen content 

 after growth without removing either the mycelium or medium prior to 

 digestion. Two types of controls were used. A number of uninoculated 

 flasks which had been stored under the same conditions as the inoculated 

 flasks were analyzed for nitrogen at the end of the experiment. A culture 

 of Azotobacter vinlandii served as a positive control. The data in Table 18 

 show that A. niger did not fix nitrogen, while P. betae and A. vinlandii did. 

 However, the nitrogen-fixing power of P. betae was slight compared with 

 that of A. vinlandii. In addition, the following fungi were tested for 

 ability to fix nitrogen, with negative results: Macrosporium commune, 

 Penicillium digitatum, P. expansum, and Glomerella gossypii. For further 



