> STEINBERG: GROWTH OF ASPERGILLUS NIGER 
period of somewhat more than six months. The evidence, though 
fragmentary, since many of the experiments had other purposes 
in view than that for which they are here utilized, is sufficiently 
full to be of value in indicating some of the factors responsible 
for the variations noted above.* 
From cultures used in previous studies (labelled as originally 
from the “‘ Internationalstelle fiir Pilz-Kulturen, Amsterdam’’), two 
one-spore strains were isolated in the following manner: 
A series of platings and transfers to agar (1 per cent. each of 
peptone, sucrose and agar) indicated that the cultures could be 
divided microscopically into two groups based on the relative 
abundance of yellow pigment in the hyphae. Two tubes were 
selected, one showing no yellow pigment and the other the maxi- 
mum amount of yellow pigment; these served as the source 
material for the isolation of two one-spore strains. 
Single drops of an agar dilution of the spores from these cul- 
tures were placed on sterile cover-glasses, and the cover-glasses 
inverted on Van Tieghem slides. These were placed in the thermo- 
stat at 30-31° C. After twenty-four hours the slides were exam- 
ined (Leitz: 4 ocular, 8 objective) and only those retained in which 
but one conidium, and this germinated, could be seen. The bit 
of agar containing this single germinated spore was at once trans- 
ferred from the coverglass to an agar slant. In another twenty- 
four hours these transfers had fruited and were again immediately 
transferréd. Great care.was taken in making this transfer not to 
touch the substratum but only the tops of the conidiophores. 
The cultures thus finally obtained are assumed to be one-spore 
cultures. They will be referred to as the W and Y strains, re- 
spectively. The presence of yellow pigment is more conspicuous 
in the latter. 
The second transfer was considered advisable as a check on 
the possible presence of other conidia (ungerminated) overlooked 
in the microscopic examination made after the first twenty-four 
hours. Since a mycelium arising from a conidium does not fruit 
within twenty-four hours, any ungerminated conidium accident- 

* In view of the results obtained by me, some of the experiments should be re- 
peated and elaborated, but since this work has been indefinitely interrupted as a 
result of my being drafted into the army, I am publishing the data as they stand. 
