18 



S. E. A. MoCallan 



able, and for Cephalothecium roseum distilled water. With each in its 

 best-suited water, germination rapidly decreases when a spore concen- 

 tration of 50 is exceeded. In no case within the experience of the author 

 has the optimum spore concentration exceeded approximately 50 spores 

 in a microscopic field of 1575 microns diameter. Indications are that 

 the germination will be slightly increased as the number of spores is re- 

 duced from 50; the difference, however, is not significant. As a general 

 rule, a spore concentration of 15 to 50 has been found the most satis- 

 factory. 



Temperature 



The temperature relations for spore germination are probably better 

 known than is any other factor. The optimum temperature for the 

 germination of the spores of any fungus should be ascertained before 

 laboratory tests are attempted. In table 5 is shown the effect of tem- 

 perature and spore concentration upon spore germination for the conidia 

 of Sclerotinia americana, and in table 6 the effect of temperature and kind 

 of water for conidia of Glomerella cingulata. 



TABLE 5. Temperature and Spore-Conoentration Relations for Conidia of 



SCLEROTINIA AMERICANA 



(Fifth transfer, 8 days old, in distilled water. Percentage germination) 



TABLE 6. 



Temperature and Water Relations for Conidia of Glomerella 

 cingulata 

 (Percentage germination) 



