390 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9. 
What significance these rapid fluctuations in temperature may have on 
the physiology of the fungi growing on or in dead twigs, the writer does 
not attempt to say, but they must have some bearing on the rate of growth 
45 6 7 8 9 10 11 M l 23 4567 8 
Fig. I. Total radiation, in gram calories per minute per square centimeter of surface, 
at Akron, Colorado. Dotted line, July 9, 1914, a clear sky. Solid line, July 11, 1914, 
a day with drifting clouds. 
and fructification of these organisms. It is evident also that the tem- 
perature environment of those fungi which grow on leaves and on twigs 
of deciduous trees must differ widely from that usually supplied them 
when grown in pure culture in heated laboratories. 
Summary 
The data presented in the present paper indicate that many plant 
parts affected by fungi often show, when exposed to the sun, a temperature 
markedly above that of the air. 
They also indicate that the fungi are sometimes subjected to fluctuations 
of temperature more rapid and extreme than the fluctuations in the tem- 
perature of the air in the shade. 
Bureau of Plant Industry, 
Washington, D. C. 
