302 BOTANICAL GAZETTE [OCTOBER 
centrations of the nitrogen compound. The nitrogen assimilated 
is approximately 2 per cent of the dry weight of the mycelium in 
all concentrations where the fungus is able to use all the nitrogen, 
in this case up to and including M/250. In higher concentration, 
where the nitrogen is in excess of what the fungus can use, the 
amount of nitrogen assimilated increases up to 5.5 per cent in the 
case of the M/ro concentration. Also, the optimum growth as 
indicated by dry weight occurred where the fungus could use all 
the nitrogen, in which case the amount of nitrogen assimilated was 
2 per cent of the dry weight. 
7. The amount of combined nitrogen taken up from the air, 
by cultures standing exposed, does not seem to be sufficient to 
make appreciable difference in their nitrogen content, either in 
nitrogen-free or in nitrogen-containing media. 
8. These fungi do not seem to be able to use nitrogen in all its 
forms, since analysis failed to show that they could use that present 
in the dextrose of the culture medium. 
9. The Kjeldahl method of analysis is capable of a degree of 
accuracy which will reduce the limit of error very near to 0.1 mg. 
for each determination in analyses involving very small quantities of 
nitrogen. In analyses involving larger quantities of nitrogen, the 
error may be reduced to 0.3 of i per cent. : 
to. A very perceptible growth of mycelium is possible in practl- 
cally nitrogen-free media, but in such cases the nitrogen content 1s 
found by analysis to fall within the limit of error of the method. 
Furthermore, the mycelium shows a starved, shriveled condition, 
as if deficient in some necessary element. In these cases, mycelia 
having a dry weight of 3-6 mg. gave amounts of nitrogen within 
the limit of error. Conversely, this may be something of a qualita- 
tive index of nitrogen-fixation, for, when the dry weight of mycelium 
1S not more than 6-8 mg., there is little or no probability of nitrogen- 
ation. — 
The writer takes pleasure in expressing his sincere thanks and 
appreciation to all the members of the Botanical Faculty of tHe 
University of Michigan for their kindly assistance and suggestions 
during this investigation. These are especially due to Professor 

