14 



II. E. Thomas and W. D. Mills 



MICRONS 



Figure 1. length of aeciospores 



minale aeciospores is 26.88 ± 0.72 fi. Measurements of aeciospore width 

 are less reliable as a means of identification. 



An attempt was made to determine whether the spore dimensions of 

 G. globosum are different on the comparatively resistant Mcintosh apple 

 from those on a susceptible species of Craetaegus. A slight decrease of 

 both length and width on the resistant suscept was noted, but, with the 

 number of spores measured, this decrease did not prove to be statistically 

 significant. 



The germination of aeciospores of these three species of fungi has been 

 accomplished at best only with considerable difficulty (Reed and Crabill, 

 1915, and Weimer, 1917). Especially poor germination has been ob- 

 tained by some Avorkers toward the end of the growing season. A few 

 casual attempts by the writers in late summer yielded negative results. 



However, it w T as noted that lesions of the apple and quince rusts on 

 apple fruits kept in a moist chamber at 3° C. for several weeks, 4 seemed 

 to enlarge somewhat and to continue the production of aeciospores. 

 An occasional aeciospore was found to have germinated in situ. Since 

 Fukushi (1925) has shown that exposure to low temperatures increases 

 the percentage germination of aeciospores of G. yamodae Miyabe, it 

 seemed probable that a similar relation might obtain for the species G. 

 juniperi-virginmnae and G. germinale. Accordingly, aeciospores of 

 these fungi were taken from the 3° chamber and mounted in raised 

 drops of distilled water at room temperature on December 6, 1928. A 



4 The material of G. r/erminale was kept in the cold chamber for approximately twelve 

 weeks, and that of O. juniperi-virginianae for ahout eight weeks. 



