224 GERMIXATIOX OF SPORES 



of temperature to infection, escape from infection, resistance, 

 and cardinal temperatures of the host. Such matters are beside 

 the present purpose but are comprehensively dealt with bv 

 Lauritzen (1919) in his studies of Ascochyta fagopyrum on buck- 

 wheat, Colletotrichum Undentuthianum on bean, and Pucc'mia 

 grandnis on wheat. It may be mentioned, how ever, that tem- 

 peratures permitting spore germination generally also permit 

 infection. In soil-borne pathogens and smuts that infect seed- 

 lings, temperature interacts with soil moisture and soil reaction, 

 and each factor is interdependent. 



The temperature relations of those fungi that produce decay, 

 especially of fruits and vegetables, have been extensively studied 

 because of their bearing on problems of storage and refrigeration. 

 YVeimer and Harter (1923) determined the cardinal temperatures 

 of several species of Rhizopus, all of which cause decay of sweet 

 potatoes in storage, to be as shown in Table 20. The first four 



TABLE 20 



Cardinal Temperatures of Species of Rhizopus Associated with Soft Rot 



of Sweet Potatoes 



Temperature {degrees C) 



species in the list may be set apart as a low-temperature group, 

 R. chinensis is a high-temperature species, and the others are 

 intermediate. 



In general, the studies on minimal temperatures that prevent 

 germination and growth of species causing decay of perishable 

 foods show that storage temperatures near 0° C must be main- 

 tained if losses are to be prevented. Hoffman ( 1860) found that 

 conidia of Penicillium glaucuvi, Botrytis vulgaris, and Trie hot he- 



