1916] 
DUGGAR AND DAVIS—NITROGEN FIXATION 415 
first-mentioned fungus, and 4.6 to 11.1 mg. in the last-named 
species. This appears to be the total amount fixed after 
growing for a period of months in 600 се. of Cohn’s solution 
with various sources of carbon. For 100 се. the nitrogen quan- 
tities would therefore be .97-1.67 and .77-1.85 mg., respec- 
tively. Fixation by Gymnoascus is also mentioned. With 
respect to analytical methods the exact procedure is not given, 
and one might, perhaps, without being too critical, wish to 
have had assurances regarding the purity of cultures, the 
nature of the vessels (‘‘ballons’’) used, and how the sample 
for analysis was taken, especially in view of the following 
remark made in regard to the amount of fixation in one of 
the series with bacteria: ‘‘Ils auraient été sans doute plus 
accusés si la dessiecation des matériaux n'avait pas fini par 
amener la mort des bactéries." 
Puriewitsch (795) used Aspergillus niger and Penicillium 
glaucum in a nutrient salt solution containing also 3 per cent 
tartarie acid, variable amounts of cane sugar, also small 
amounts of ammonium nitrate. He obtained a mean nitrogen 
fixation of 4.51 mg. for Aspergillus, and 3.26 mg. for Penicil- 
lium. It is not stated whether these amounts are calculated 
on the basis of 100 ce. of solution, or whether they were for 
25-50 ce., the quantities which appear to have been used in 
the different cultures. At the same time he reported that the 
amount of fixation inereased with the concentration of sugar, 
but did not increase in direct proportion to the increase in 
weight of the mycelium. It is not clear, though quite possible, 
that these results were obtained with pure cultures. More- 
over, since in some of the cultures, at least, dry weight de- 
terminations of the fungous felt were made, the conclusion is 
unavoidable that herein might be a possibility of error. Like- 
wise, the division of some of the experiments into ‘‘(a)’’ and 
“(b)” suggests that the whole of the solution was not em- 
ployed in the analysis. The results were subsequently eriti- 
cized by Czapek (701) and Heinze (706) on other grounds. 
The fact that fungi may make an appreciable growth on 
media eontaining a very low minimum of nitrogen, without 
nitrogen gain, has been pointed out by some investigators, 
