ENVIRONMENTAL TEMPERATURES OF FUNGI IN NATURE 
Neil E. Stevens 
(Received for publication December 12, 1921) 
The relation between environmental temperatures and the development 
of certain fungi — particularly plant parasites — has been the subject of 
recent study by several investigators.^ The results of these studies, while 
highly suggestive, have, of necessity, been somewhat inconclusive because 
the only material available has consisted of the temperature relations of 
certain fungi as determined by their behavior in pure culture and of climatic 
temperatures, i.^., the temperature of the air in shade. The unsatisfactory 
nature of comparisons made on this basis has been frankly recognized 
by most of the investigators. Fawcett, for example, remarks in his in- 
troduction (p. 184) : 
Most organisms (aside from warm-blooded animals) are never exposed, in nature, 
to maintained temperature for any considerable period of time; their temperature environ- 
ment is practically always in a state of flux. From this it follows that a knowledge of 
the relation holding between maintained temperatures and vital processes, no matter how 
thorough such knowledge may be, can not be expected to be a complete basis for an in- 
terpretation of physiological processes going on under natural conditions. 
The study of the relation of fungi to their environment is, however, 
still more complicated by the fact that, as the present notes show, the 
plant parts living or dead upon which many fungi grow are often, when 
exposed to the sun, at a temperature much above that of the air. The 
temperature of these plant parts, moreover, apparently fluctuates under 
certain conditions much more rapidly than that of the air in the shade. 
That the twigs of living peach trees when exposed to the sun often 
reach a temperature well above that of the air was pointed out over twenty 
years ago by Whitten.^ His observations, however, were made chiefly in 
winter, and the greatest difference he records is 8° C. (air 2.7° C; twig 
10.7° C). 
In a series of observations made incidentally during the summer of 
192 1, much greater differences between the temperature of the air and 
that of twigs exposed to the sun were frequently observed by the writer. 
The temperature readings here recorded were all made with mercury ther- 
mometers especially made for the work, having cylindrical bulbs 2 mm. 
1 Most of these papers are cited in Fawcett, H. S. The temperature relations of 
growth in certain parasitic fungi. Univ. Cal. Pub. Agr. Sci. 4:183-232. 1921. 
2 Whitten, J. C. Das Verhaltnis der Farbe zur Totung von Pfirsichknospen durch 
Winterfrost. Pp. 1-34. Halle, 1902 (and earlier publications). 
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