396 



FUNGOUS DISEASES OF PLANTS 



upon Trifolium incarnatum L., much less frequently, however, upon 

 some of the other species mentioned. In general, the spermogonial 

 and aecidial stages are not commonly found upon the red clover, 

 the host upon which the other stages are perhaps most frequent. 



Nevertheless, the reported 

 absence of gecidial stages 

 upon this host in certain 

 regions may be due to the 

 fact that careful examina- 

 tions have not been made 

 at the proper season. 



The fungus. The my- 

 celium corresponds very 

 closely to that described 

 as generally characteristic 

 of the whole order. It is 

 considered to be local. 

 The spermogonia and 

 aecidia generally appear 

 during very early spring 

 or at almost any time dur- 

 ing open winter. They 

 occur upon the under sur- 

 faces of the leaves and on 

 the petioles. The secidio- 

 spores (14— 23/i in diam- 

 eter) germinate readily in 

 water, and under favor- 

 able conditions infection 

 in the greenhouse or in 

 the open may be secured, 

 with the production of uredosori within two weeks. The uredo- 

 spores, as shown in Fig. 195, d, measure about 22—26 x 18-20 p. 

 These spores also germinate readily, and repeated crops of the 

 uredospores may be produced, possibly in some cases extending 

 into the winter, and even carrying the fungus through the year. 

 Teleutospores are produced, however, and these may occur in 

 sori with uredospores, or in independent sori, as the season 



c a 



Uromyces Trifolii: Clover Rust 



