1916] 
DUGGAR AND DAVIS—NITROGEN FIXATION 423 
months. For each species he claims positive results, the fixa- 
tion ranging from 0.8575 mg. in the lowest to 1.8615 mg. in 
the highest, per 100 ec. of solution. The inference seems to 
be that in each case a single inoculated culture or a single con- 
trol was usually employed. It is of interest to note that 
aside from the few analyses made, the fungous felt and the 
solution were separately analyzed. 
Traaen (714) made no quantitative studies to determine N- 
fixation, but he observed the growth of 4 fungi on media prac- 
tieally nitrogen-free, and as a result of the very weak growth 
he came to the conclusion that under the conditions they could 
not possibly utilize atmospheric nitrogen. 
Using strains of Aspergillus niger and Penicillium glaucum, 
Chambers (716) was unable to demonstrate any N-fixation. 
He employed Folin’s micro-Kjeldahl method, growing the 
organisms in long Jena test-tubes and making the determina- 
tions without transfer of any portion of the culture. 
METHODS 
The organisms used in this work were Aspergillus niger, a 
strain long employed in various physiological experiments in 
this laboratory; a species of Penicillium, isolated from leaves 
and corresponding closely to Thom's idea of P. expansum; 
P. digitatum, isolated from a decaying orange; Macrosporium 
commune, isolated from dried grass culms; Phoma Betae, a 
culture obtained through the kindness of Mr. E. C. Rittue, Los 
Angeles, California; and for comparison three forms of Azoto- 
bacter, as follows, all three being furnished by Dr. J. G. Lip- 
man, A. vinelandii, A. chroococcum (from Kansas soil), and 
A. chroococcum (from Colorado soil). 
Except as to the source of nitrogen and carbon, there has 
been no great dissimilarity in the mineral nutrient solutions 
employed by European investigators. The Cohn solution or 
a modification of it has been the basis of much of the foreign 
work. We wished to have some of our experiments follow 
fairly closely the work of Saida, therefore we have used in 
1 The NE and cultural characters of this organism will be described 
in a subsequent paper 
