I.O W T I M V I R AT I' RE 



425 



Figure 1. The order of killing 

 of ascospores of Byssoclilarnys 

 fulva by moist heat (85°C). 

 Replotted from Hull (70), by 

 permission of the Cambridge 

 University Press. 



40 



Time, minutes 



80 



The mechanism of death at high temperature is usually thought to 

 be denaturation of proteins; the high Q 10 of thermal death (128) is 

 consistent with this explanation. Whatever the validity of the de- 

 naturation theory at high temperatures, some other explanation must 

 be invoked to explain death at temperatures which are just above the 

 maximum for development. Thus, mitosporangia and sporophytic 

 mycelium of Allomyces sp. die within 24 hours at 30° (98), and uredo- 

 spores of Phraginidiam mucronatum survive only 12 hours at 27° (22). 

 Presumably some fraction of metabolism continues under these condi- 

 tions, and either endogenous reserves of essential materials are de- 

 pleted or essential cofactors decay and cannot be resynthesized. Less 

 likely, but possible, is the accumulation of one or more metabolites in 

 toxic concentrations. 



2. LOW TEMPERATURE 



No systematic study of damage to fungi by low temperature has been 

 reported. Even more important, the scattered data have been obtained 

 under such different experimental conditions that comparison and 

 generalization must be very tentative indeed. Too often we are not in- 

 formed of essential factors, particularly (1) the type of cells present, 

 (2) the quantitative degree of injury, (3) the rate of freezing, and (4) 

 the rate of thawing. It must be realized that survival can only be 



