18 BULLETIN 395, U. S. DEPARTMENT OF AGRICULTURE. 



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 Lima-bean and beerwort agars and steamed string-bean pods. 

 At 2° C. tbe growth was very gradual, becoming 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 24°, being, perhaps, slightly 

 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 24°. 



It appears, therefore, that the minimal temperature for growth of 

 the fimgus 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 in 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 sunhght for several hours of each clear day. Inas- 

 much as no effort was made to segregate the effects of Hght and 

 temperature, these experiments merely showed that cultures which 

 had been frequently exposed to direct sunhght under these conditions 

 appeared to suffer no permanent injury, their ultimate development 

 being good. 



It appears, therefore, that strong diffuse Hght 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 imder varied conditions. Only certain general 

 aspects of the results will be considered here. Data regarding via- 

 bihty are given in another connection (p. 35). 



