52 BOTANICAL GAZETTE [JANUARY 
deserves mention, although the percentage of germination is not 
great. 
Oxalic acid stands quite alone as a substance stimulating 
Sterigmatocystis more than Aspergillus, in fact causing its 
maximum stimulus at a concentration which affords no germina- 
tion with Aspergillus. This effect on Sterigmatocystis was so 
variant and marked that this acid is to be regarded as a peculiar 
stimulant for that plant. 
: THE INFLUENCE OF CERTAIN PHYSICAL STIMULI. 
From some variations in results obtained it became evident 
that by the form of the drop and the amount of evaporation 
therefrom, or perhaps by some other physical force closely con- 
nected with these conditions, a considerable stimulus was given 
to germination. When the cultures of Aspergillus flavus were 
prepared at the same temperature at which they were to be 
incubated, with all possible precautions being observed as to 
purity of water and cleanliness of cover glasses, there was seldom 
more than a fraction of I per cent. of germination, provided the 
culture drop retained its original form and dimensions. In 
cases of some evident change of conditions within the culture, 
however, whether by slight dispersal of the drop or by a certain 
amount of evaporation, the percentage of germination was often 
greatly increased. In special cases the percentage of germina- 
tion was as high as go after an incubation of fifteen hours, this 
maximum being reached particularly when the spores were free 
from each other and collected on the periphery of the drop next 
to the glass. 
Many experiments were introduced with the hope of eliminat- 
ing the single factors which might be involved and of accurately 
determining the cause of the stimulus. Unfortunately the matter 
is as yet very inconclusive. 
If even very small amounts of some salts were present in the 
drop, these during evaporation would be concentrated at the 
periphery, especially at the edge in contact with the glass. 
This would hardly be sufficient, however, to account for the 



