64 



James G. Horsfall 



\0* 



Figure 15. lesions caused by pseudoplea trifolii on leaves of white clover 



may become larger but the colors are about the same. The center of the 

 larger spots tends to crumble away, leaving a ragged edge. Miles (1925: 

 678) reports lesions on stems, peduncles, calyx, corolla, and even on the 

 seed of Medicago maculata. 



Leaves may turn yellow and absciss when the lesions become very 

 numerous on the petioles or blades. When this condition obtains to a 

 marked degree in white-clover lawns, the whole stand appears yellow and 

 sickly. Defoliation occurs on all the suscepts. 



Etiology 



Name, history, and classification of the pathogeny. The organism has 

 received several names by different investigators. A very brief review of 

 the history of its nomenclatorial vicissitudes will best serve to present the 

 evidence upon which the writer has based his own decision in the matter. 

 Rostrup (1899) first named it Sphaerulina trifolii from white clover in 

 Denmark. Hopkins applied this name to a fungus on red, white, and 

 alsike clovers which he reported for the first time in America in 1923. 

 This fungus was described as having asci bearing eight hyaline, three- 

 septate spores, 30 to 33/* by 12 to 15/* in size. Pleosphaerulina briosiana 



