[Vor. 8 
416 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
and may adequately explain Fermi’s (’96) statement to the 
effect that he was able to grow certain moulds and yeasts on 
nitrogen-free media without nitrogen fixation. 
Brefeld (’00) determined that cereals and grasses infected 
with species of Ustilago were unable to assimilate free nitro- 
gen, but this type of negative evidence is valueless in the 
present discussion. 
More extensive than any of the earlier work is that reported 
by Saida (’01) who investigated seven species, three of which 
(Phoma Betae, Mucor stolonifer, and Aspergillus niger) give 
nitrogen fixation both with and without the presence of com- 
bined nitrogen in the culture medium, one species (Endococ- 
cus purpurascens) requires the presence of combined nitro- 
gen, and three species give negative results. In most cases 
the fungi were grown on 50 ce. of nutrient salt solutions con- 
taining dextrose or cane sugar, the source of nitrogen being 
a small quantity of (NH4)2SO4 or of (КН.)„СОз. In none 
of the four species except Phoma Betae is the amount of fixa- 
tion more than about 2 mg. (.8871-2.0699 mg.). Fixation 
(varying from 1.1828 to 10.536 mg.) in P. Betae rises some- 
what in relation to sugar content of the medium, although 
maximum fixation occurs in sugar beet decoction plus sugar. 
The exact method of handling the cultures is not described, 
but with the exception of possibilities mentioned later, the 
work seems to be above criticism. 
Czapek (201) states that Aspergillus niger does not fix free 
nitrogen. Later, as a result of numerous experiments on 
nitrogen-containing media Czapek (’02) again reports no 
fixation for this species. He declares that the work of Purie- 
witsch and Saida requires confirmation. 
Studying the effects of a yeast and a mould on the nitro- 
gen fixation of Azotobacter, Gerlach and Vogel ('03) con- 
clude from analyses of the control cultures, in which each of 
these organisms was grown alone, that neither of the former 
fungi are capable of utilizing atmospheric nitrogen. 
Koch (’03) was unable to demonstrate any nitrogen fixa- 
tion for Aspergillus niger in a few preliminary experiments. 
He draws attention, however, to an experiment made by 
