308 



PHYSIOLOGY OF THE FUNGI 



produced abundant perithecia and ascospores at 25°C. within 11 days. 

 Conidia were formed at 18°C. 



The most noteworthy effect of culturing a fungus at temperatures 

 below the optimum is the decrease in the rate of growth. It has been 

 found by various investigators that there is an optimum temperature for 

 sporulation as well as for growth. The two optima may be different. 

 Figure 57 shows the effect of temperature on the time required to produce 

 conidia by Aspergillus repens. 



14 



12 



10 



2 6 



Q, 4 



o 

 o 



10 15 20 25 30 



Temperature in degrees centigrode 



35 



40 



Fig. 57. The influence of temperature on the time required to produce conidia by 

 Aspergillus repens. (Drawn from data of Klebs, Jarhh. wiss. Botan. 35 : 137, 1900.) 



A temperature of 28°C. was optimum for sporulation of Piricularia 

 oryzae (Henry and Andersen, 1948). Higher and lower temperatures of 

 incubation decreased the numbers of spores produced. At 32°C. the 

 number of spores was only 10 to 15 per cent of that produced at the 

 optimum temperature. Reducing the temperature of incubation to 

 24°C. reduced the numbers of spores to about 80 per cent of the maxi- 

 mum. Thus, a small temperature increase above the optimum has a 

 much greater effect upon the number of spores produced than a small 

 decrease in temperature below the optimum (Fig. 58). 



In nature, fungi are exposed to fluctuating temperatures. Whether a 

 fluctuating temperature is more favorable in inducing sporulation than a 

 constant temperature appears to have been studied but little. Jones 

 (1946) concluded that temperature was the important controlling factor 

 in the production of resistant sporangia of Allomyces arhiiscula in culture, 

 and he beheved that "the total amount of temperature" to which the 

 cultures were subjected was more important than the maximum, mini- 



