176 Nitrogen Fixation by Yeasts 



with which Zikes worked and which fixed considerably more 

 nitrogen. 



That fixation should further have taken place in cultures repre- 

 senting the various classes of organisms experimented with, 

 confirms the writer in the belief which he has held ever since these 

 investigations were begun that the power of fixing atmospheric 

 nitrogen though perhaps not a universal one among the lower 

 plants is yet a very widespread power among the fungi. The 

 fixation of nitrogen by true yeasts is, so far as the writer is aware, 

 the first one described as such in the literature on the subject and 

 adds another class of organisms to the now rapidly growing list 

 of those which seem to be possessed of that power. It must 

 also be mentioned here that the culture solution used above 

 while a very good one for organisms of the Azotobacter group is 

 not necessarily a satisfactory one for the organisms studied and 

 was only employed because of the fact that so many different 

 organisms were used and further obviously that no information 

 is available as to what constitutes a good medium for nitrogen 

 fixation for each class of organisms tested. It is possible, for 

 example, that the alkaline reaction of the culture solution which 

 is so necessary to the fixation of nitrogen by Azotobacter may be 

 rather a hindrance than otherwise to the nitrogen fixing powers 

 of Aspergillus niger or even the yeasts. Despite that, however, 

 we have evidence of a power of nitrogen fixation, more or less 

 pronounced, in each of these classes of organisms. 



Series II. 



Owing to the fact that the zymologist values dextrose so highly 

 as a medium for fermentation by yeasts, it was decided to arrange 

 a series like the preceding but to substitute dextrose for mannite. 

 The solutions were distributed in 100 cc. portions in 500 cc. 

 Erlenmeyer flasks as described in the first series, and after the 

 requisite sterilization and cooling were inoculated from the beer 

 wort cultures of the organisms tested. The incubation was 

 carried out in the same manner as in the preceding series, after 

 which the solutions were analyzed for nitrogen according to the 

 modification of the Kjeldahl method above described. The 

 results of the analyses follow: 



