1916] 
DUGGAR AND DAVIS—NITROGEN FIXATION 435 
decay. If it should be positively demonstrated, therefore, 
that the fungi concerned in this disintegration are at the same 
time capable of fixing an amount of nitrogen sufficient to 
prove of practical value, then it would be clear that agricul- 
tural practice might be modified in many ways to make greater 
use of this possibility of nitrogen enrichment accompanying 
the decay of herbage. As a matter of fact, however, the 
amount of fixation, as we have seen, reported for Alternaria, 
Macrosporium, Cladosporium, Aspergillus, Penicillium, ete., 
even by those recent investigators who claim fixation, is very 
slight—indeed, for such organisms it is usually considerably 
below 5 mg. per 50 сс. of solution. Assuming that there might 
be as much fungous felt in 1 cubic foot of ordinary soil as in 
100 ce. of a culture! and that in both cases the amounts of fixa- 
tion might be equal, we would have as a maximum 10 mg. nitro- 
gen fixed per cubic foot or 420,000 mg. per acre, 1 foot deep, 
that is, 420 grams per acre, or about one pound. When it is 
recalled that in many cultures of Azotobacter the fixation has 
been as high as 50-200 mg. per 100 cc., and when it is further 
remembered that in the soil the conditions favor quantity of 
bacterial rather than fungous growth, we may perhaps gain 
some conception of the impracticability of claiming an eco- 
nomie relation in respect to nitrogen for such fungi. 
SUMMARY 
L A review is given of all available literature relating to 
nitrogen fixation by the fungi. 
2. Culture and analytical methods are discussed, and sug- 
gestions are made with a view to the elimination of certain 
possible errors involved in this type of work. 
9. Nitrogen fixation could not be demonstrated for Asper- 
gillus niger, Macrosporium commune, Penicillium digitatum, 
P. expansum, and Glomerella Соззури. 
4. In eultures of Phoma Betae on mangel and on sugar 
1 This seems highly EE in the light of recent discussion of this point; 
compare the following: Conn, H. J. Relative importance of fungi and bacteria 
in soil. Science N. 8. 44: 857-858. 1916. 
