18 BULLETIN" 395, U. S. DEPARTMENT OB AGBICULTUBE. 
RELATIONS OF TEMPERATURE. 
Several series of cultures were incubated in darkness at carefully 
controlled temperatures ranging from 2° to 40° C. The media used 
were Lirna-bean and beerwort agars and steamed string-bean pods. 
At 2° C. the growth was very gradual, becom ing barely macroscopic 
in about a month. At 4° and 6° C. the development was slightly 
more rapid, while at 9° and 12°. respectively, it was conspicuously 
accelerated. The rapidity of growth increased steadily up to 20° C, 
while at 24° a slight increase over 20° could be observed. At 27° C. 
the development closely paralleled that at 2-1°, being, perhaps, shghtly 
less rapid. At 30° to 32° C. the fungus rarely became macroscopic, 
while no growth occurred at 35°. Cultures incubated for three weeks 
at 35° C. developed vigorously, however, when the temperature was 
decreased to 2-±°. 
It appears, therefore, that the minimal temperature for growth of 
the fungus on favorable substrata is less than 2° C; the optimal, 
between 20° and 27° — about 25°: and the maximal, about 32°. 
RELATIONS OF LIGHT. 
Numerous cultures on Lima-bean and beerwort agar slants and 
steamed string-bean pods were incubated comparatively side by side 
in strong diffuse light and in darkness, at temperatures ranging from 
20° to 25° C. Excellent development resulted hi all cases, the cul- 
tures of the two series being practically indistinguishable, except for 
the fact that sporulation was uniformly distinctly more abundant 
in the case of those grown in light. Good sporulation, however, 
occurred in the cultures grown in darkness. 
In certain cases, in January and February, parallel cultures were 
incubated for several weeks in a south window, where they were 
exposed to direct sunlight for several hours of each clear day. Inas- 
much as no effort was made to segregate the effects of light and 
temperature, these experiments merely showed that cultures which 
had been frequently exposed to direct sunlight under these conditions 
appeared to suffer no permanent injury, their ultimate development 
being good. 
It appears, therefore, that strong diffuse light exerts no marked 
influence on the vegetative development of the fungus, but dis- 
tinctly favors sporulation. 
Spore-Germination Studies. 
More than a thousand germination tests were made with conidia 
from various sources under varied conditions. Only certain general 
aspects of the results will be considered here. Data regarding via- 
bility are given in another connection (p. 35). 
