356 PHYSIOLOGY OF THE FUNGI 



the usual favorable conditions to activate a certain enzyme. Some 

 special stimulus may then be required to perform this function. 



The present discussion deals primarily with the factors which influence 

 some physiological phase of spore germination. The main emphasis 

 will be placed upon a discussion of these factors and how they act, or 

 what part they play in germination. Doran (1922) gives a good discus- 

 sion of the more important factors affecting germination and lists many 

 references to the earlier work. A more recent discussion of this subject 

 is given in the excellent review by Gottlieb (1950). 



PHYSICAL FACTORS 



Temperature. Temperature is one of the most important external 

 factors which influence germination. It not only affects the percentage 

 of germination but also the length of time required for germination, and, 

 in certain fungi, it often determines the method of germination. The 

 literature contains a great many references to spore germination at dif- 

 ferent temperatures, but none of these have attempted to explain the 

 intricate effects or responses within the spore. We may assume that a 

 favorable temperature permits certain enzymatic activities essential to 

 germination. Different species of fungi have different temperature 

 requirements for germination. The cardinal temperatures (minimum, 

 optimum, and maximum) for spore germination may be found for many 

 fungi in scattered reports. These are based mainly on casual observa- 

 tions made during the study of other problems. Few comprehen- 

 sive studies have been made of the effects of temperature upon spore 

 germination. 



The cardinal temperatures of a few selected species are presented as 

 examples: AUernaria solani, 1 to 3°C., 26 to 28°C., 37 to 45°C. ; Cronartium 

 rihicola aeciospores, 5°C., 12°C., 19°C.; Phyllosticta antirrhini, 18°C., 

 25°C., 'i7°C. ■,Phytophthora infestans, 2 to 3°C., 12 to 13°C., 24 to 25°C.; 

 Puccinia graminis teliospores, 5 to 9°C., 20 to 22°C., 23 to 25°C. ; Venturia 

 inaequalis conidia, 3°C., 14 to 15°C., 31°C. For other examples, see 

 Doran (1922). 



The general optimum temperature for spore germination of certain 

 species of Agaricaceae and Nidulariaceae is near 30°C. (Kauffman, 1934). 

 Walker and Wellman (1926) found that, when the soil temperature was 

 above 25°C., there was low percentage of "chlamydospore" germination 

 of Urocystis cepulae, while spore germination ceased entirely at 29 or 

 30°C. They attribute the low percentage of infection above 25°C. to the 

 direct inhibitory effect of the higher temperature upon the parasite. 



The presence of nutrients and the supply of oxygen caused variation 

 in the minimum temperature for spore germination in Colletotrichum 

 lagenarium (Gardner, 1918). The minimum was 14°C. in water with the 



