FIXATION OF NITROGEN BY FUNGI 179 



gillus niger that confirms the results of the earher investigators. 

 She states that the amount of fixation by molds is so imper- 

 ceptibly small as compared with that of bacteria as to throw 

 doubt upon the reliability of the Kjeldahl method for making 

 such determination with sufficient accuracy. Two of the six 

 sources of error mentioned by her, as found in the use of this 

 method are : 



(1) inaccurate titrations (standardization) of t^ solutions as 

 commonly used in this method. 



(2) lack of sharpness in color indicators. These two sources 

 of error are largely eliminated by the colorimetric method. 



The work and results of Latham^ present the most striking 

 puzzle; first in the enormous amount of fixation given in some 

 cases, and secondly in the great variance in her figures, e.g., 

 from 44.9 to 193.6 mg. in 50 cc. of culture solution. Her state- 

 ment that nitrogen is consumed by the fungus from the culture 

 solution in proportion to stimulation, is the characteristic point 

 in her work but does not seem to receive full explanation. 



Lipman^ is the most recent investigator to report fixation by 

 Aspergillus niger and his results are far from small, but seem to 

 be consistent. He has nothing special to say in regard to any 

 special methods by which these large results are obtained. 



When we turn to the list of those who have reported negatively 

 on Aspergillus niger we are confronted by a dearth of data 

 except in the work of Czapek already mentioned. His work 

 was not directed specially toward the question of fixation but 

 is limited to the simple statement that no fixation could be 

 detected though diligently sought for. 



From Winogradsky^ we have very little more than the bare 

 negative statement; but this statement, from so prominent an 

 authority on this subject, together with that of Czapek must 

 carry great weight. 



^ Latham, Marion E., Nitrogen assimilation of Sterigmatocystis nigra and the 

 effect of chemical stimulation. Bull. Torr. Bot. Club 36: 235-255. 1909. 



* Lipman, Chas. R., Nitrogen fixation by yeasts and other fungi. Jour. Biol. 

 Chem. 10: 169-182. 1911-12. 



^ Frohlich, H., Stickstoffbindung durch einige auf abgestorbenen Pflanzen 

 hiiufige Hyphomyceten. Jahrb. f. Wiss. Bot. 45: 256-302. 1908. 



