98 EFFECTS OF TEMPERATURE ON FUNGI 



Fawcett (1921) indicate that the optimum cannot be considered 

 apart from the time factor. 



The temperature range within which fungi are active is rather 

 limited in comparison to that of bacteria. At 0° C their growth 

 is completely checked, and relatively few are active at 42° C. 

 The optimum temperature is not median in any instance between 

 the minimum and the maximum temperatures. In other words, 

 temperature does not increase the rate of fungus activity uni- 

 formly from the minimum to the optimum, and decrease it uni- 

 formly from the optimum to the maximum. 



In connection with the rate of reaction (physiological proc- 

 esses) in fungi, the {generalized rule of van't Hoff, which states 

 that for every rise of 10° C the reaction rate is doubled or trebled, 

 holds true, within the range approximating 10° C to 30° C. At 

 high temperatures, however, as Blackman (1905) has indicated, 

 this rule is modified by a time factor, for ". . . when the process 

 is conditioned as to its rapidity by a number of separate factors, 

 the rate of the process is limited by the pace of the 'slowest 

 factor.' Such controlling factors are sometimes spoken of as 

 "pace-makers." Their influence is universally demonstrated in 

 graphs showing cardinal temperatures in all fungi studied. The 

 growth curve is observed to decline sharply and precipitously 

 from the optimum to the maximum. In Table 8 are assembled 

 the cardinal temperatures for a few representative species grown 

 on semisolid media. 



The most extensive study to date involving temperature in rela- 

 tion to the growth of fungi capable of producing decay of wood 

 is that of Cartwright and Findlay (1934). They measured the 

 diameter of colonies grown on 2% malt agar, using the average 

 daily increment of growth of five colonies as an index. Their ob- 

 servations are summarized in Table 9. 



From these data it is apparent, first of all, that the temperature 

 requirements of species within the families Thelephoraceae, Polv- 

 poraceae, and Agaricaceae are variable between species, even 

 within the same genus. 



Cartwright and Findlay (1934) indicate that comparative 

 growth rates on malt agar may not necessarily indicate the growth 

 rates on timber in the forest. Stereum purpureum, for example, 

 grows rapidly on malt agar but slowly on wood. Nevertheless 

 a given wood-destroying species, such as S. frtistitloswn on oak, 



