108 EFFECTS OF TEMPERATURE ON FUNGI 



of the protoplasm bv ice crystals; (3) crushing between the ice 

 masses as freezing progresses; (4) thawing at too rapid a rate; (5) 

 dehydration of protoplasm, resulting in increased permeability, 

 increased viscosity, coagulation of proteins, ionic dissociation, loss 

 of water-binding properties of cytoplasm, and or svneretic re- 

 lease of water. 



High temperatures. Fungi, it has been pointed out, generally 

 are unable to tolerate exposure to high temperatures. The de- 

 cline in ability to germinate or to grow is normally very sharp in 

 the zone beyond the optimal. 



The lethal effects of temperature on germination of spores is 

 considered in Chapter 9 and therefore need not be discussed here. 

 In many instances such temperatures as inhibit germination and 

 growth or are lethal are not excessive. For example, Wolf et al. 

 (1934) found that sporangia of Peronospora tabacina exposed to 

 85° F for 1 hour are incapable of germination. 



Fawcett and Barger (1927) observed that oranges kept at 90.5° 

 F, which is above the maximal limit for Pemcillhmi italicum and 

 P. digitatimi, are not decayed during 28 days' exposure. On the 

 other hand, Faull (1930) noted that the ascospores of Neurospora 

 crassa, when heated for more than 1 hour at 50° C, retain their 

 ability to grow. 



In the fermentation of cigar tobaccos, temperatures of 140° to 

 150° F are not unusual. Aspergillus niger, commonly present on 

 the cured leaves, is unable to develop at these temperatures but 

 may induce spoilage if too much time elapses for the bulk to be- 

 come hot or to cool after fermentation. Temperatures near 100° F 

 approximate the optimum for this mold. 



Treatment with hot water has been employed to free seed oats 

 from loose smut, caused by Ustilago avenae, and wheat from 

 naked smut, caused by U. tritici. Such treatment is practicable 

 because the temperature lethal for the smut fungi is lower than 

 that which kills the cereal embryos. Similarly, cotton seed, if 

 slowly desiccated, can be rendered free from viable external 

 conidia and internal mycelium of the anthracnose fungus, Glomc- 

 rella gossypii. Lehman (1925) predried cotton seeds at 50° C, 

 for 36 hours or at 60° C for 18 to 24 hours and then heated their; 

 to 95° C for 10 to 12 hours, without reducing their percentage 

 germination and with complete elimination of the anthracnose 

 fungus. 



