298 BOTANICAL GAZETTE [OCTOBER 
analyses show still smaller gains. In any case, these results could 
only show that the fungi under these conditions had been able to 
use a very small amount of the combined nitrogen, which the analyses 
of controls has shown to be present in the dextrose. All preceding 
evidence of this investigation has been against this idea, and we 
are strongly inclined to hold to the idea that these results are due 
to slight variations in the accuracy of the method of analysis. 
Another interesting and perhaps important fact may be seen from 
the last table. The amount of nitrogen present in the mycelium is 
not proportional to the dry weight. This point was suggested earlier 
in the examination of mycelia grown in nitrogen-free media, where 
the hyphae looked somewhat shriveled and starved, as if the proto- 
plasm lacked some necessary constituent. It appears here that 
the mycelium has the power of taking up a higher amount of 
nitrogen than it really needs for the best growth, judging best 
growth by the amount of dry weight, for in the two higher concen- 
_ trations a larger percentage of nitrogen is shown, even though the 
dry weight is much less than in the M/2s50 concentration. The 
amount of nitrogen is also proportionally higher for the M/1o than 
for M/s50. This holds for both series of cultures. If we take the 
averages of the two series, the per cents of nitrogen in dry weight 
of mycelium are approximately as follows: M/r10, 5.5 per cent; 
M/s50, 5 per cent; M/250, 2 per cent; M/r250, 1.8 per cent; 
M/6250, 2 per cent. Or, stated more generally, the fungus will 
assimilate about 2 per cent of its dry weight of nitrogen when this 
is supplied in. such quantities that the fungus can use all that 1s 
present, but when the nitrogen is in excess of what the fungus can 
use, then a larger percentage is assimilated, running as high as 5-5 - 
per cent. The evidence seems too scanty to make certain whether 
such a generalization would hold in all cases. Why this larger pet- 
centage of nitrogen is present in the solutions of higher concen- 
tration does not seem apparent. It may be that the presence of 
nitrogen compounds in excess causes the fungus to use these 
Instead of carbon compounds, which are used in greater quantity 
when the nitrogen supply is limited. This investigation can only 
Taise this question, and suggest its value as a subject worthy of 
further physiological investigation. 
