Three Rust Diseases of the Apple 



15 



considerable number of the spores of both species germinated. More 

 extensive tests were then made at various temperatures, and the results 

 were indeed surprising (table 6, and Plate I, 3 A). We find no record, 



TABLE 6. Germination of Aeciospores Following Exposure to Low Temperatures 



(3° C.) 



in the literature, of germination approaching that recorded here for 

 the aeciospores of these species. The germ tubes were vigorous, and 

 reached a length of 400 to 600 /x in twenty-four hours, even at 9° C. 



On December 14, fallen Crataegus fruits bearing G. germinale were 

 collected at Ithaca, New York. The fruits were browned and more or 

 less mummied in appearance, and the open aecia no longer contained 

 spores. However, a few aecia were found which had never opened, and 

 spores from these were mounted at 9°, 12°, and 15° C. for germination. 

 Even here a germination of respectively 1, 2, and 3.5 per cent was 

 obtained. 



A single mount of aeciospores of G. globosum collected on December 

 12, 1928, on fallen Crataegus leaves, showed 54 per cent germination 

 after twenty-six hours. The only appreciable germination reported for 

 this species by Weimer (1917) was obtained from material exposed out- 

 doors until November 8. 



In view of these results and the successful inoculations made by 

 Dodge (1918) and others, there seems no longer any reason to question 

 that aeciospores of these fungi may produce infection during the 

 season in which they are produced. It seems probable that the greater 

 part of the natural infection on cedars will be found to take place 

 in late autumn, rather than in midsummer or the following spring 

 as has been suggested by various workers. Further studies arc needed 

 to provide direct evidence of the time and manner of infection of the 

 cedar by each of these fungi. 



It has been pointed out that the peridial cells of the three fungi differ 

 in size as well as in shape and sculpturing (Plate I, 3, 4, and 5). The 

 dimensions of these cells are more definitelv recorded in figures 2 and 3. 



