A Study of Meadow-Crop Diseases in New York 



31 



Life history. The general features of the life history of the clover-rust 

 fungi appear to be those of similar autoecious long-cycled rusts. The 

 telia overwinter on debris of diseased plants, where they produce the 

 sporidia in the spring that infect the young leaves and produce aecia. 

 No detailed studies appear to have been made of the phenomena of 

 inoculation, incubation, and infection in the primary cycle in any of the 

 clover rusts. 



Aecia of the primary cycle furnish the inoculum for the first secondary 

 cycles, and uredinia serve in the same capacity for the subsequent secondary 

 cycles. Both aeciospores and urediniospores are borne by the wind to 

 new infection courts. 



For germination studies with the rust spores, leaves bearing fresh sori 

 were collected in the field. The spores were washed from these leaves 

 into Syracuse watch glasses with a stream of aerated distilled water from 

 a wash bottle, as suggested by Doran (1922), in order to get mature spores 

 and to avoid injuring them. The data on white- clover rust are very 

 inconclusive because of the difficulty in obtaining good germination of the 

 spores used as checks. It is assumed that no valid conclusions can be 

 drawn when the percentage of germination of the checks is less than 90 

 per cent. 



To study the role of temperature in germination, duplicate slides of 

 urediniospores were placed at various temperatures in the incubators. 

 The data presented in table 12 are based on an average of several such 

 experiments. 



TABLE 12. 



Effect of Temperature on Urediniospore Germination of Uromyces 

 Trifolii Hybridi and Uromyces Trifolii Fallens 



It appears that 3° C. is somewhat too low for good germination for both 

 fungi, and that 33° C. is entirely loo high. There is, nevertheless, a wide 

 range of temperatures within which these spores readily germinate. Little 



