60 James G. Horsfall 



reached. They then enlarge somewhat and become angular in shape, since 

 the vein seems to limit the radial growth. At this stage the black blotches 

 appear mealy because of the conidiophores and spores that are present. 

 In the autumn these velvety black, somewhat elevated patches are replaced 

 by other black areas which are shiny above but appear warty if examined 

 closely. The warts are the openings of the pycnidia which develop at 

 this stage. 



As the black patches, or stromata, grow, the leaf yellows somewhat 

 immediately about them. This is evident on the dorsal side of the leaf 

 directly above each stroma. A casual glance might confuse this aspect 

 of the malady with clover rust. With increasing secondary infections, 

 the yellowed areas spread, finally causing the entire leaf to die and fall 

 off. As already pointed out, Killian (1923) maintains that sometimes, if 

 the infection is slight, the diseased leaves remain green longer than healthy 

 ones. Bayliss-Elliott and Stansfield (1924:219) in England state that 

 " the leaflets of the infected leaves take an upright position and are thus 

 easily distinguished from healthy leaflets which are extended horizontally." 



Etiology 



Name, history, and classification of the pathogene. SoOty b otch of 

 clover is caused by Dothidella trifolii (Fries) Bayliss-Elliott and Stans- 

 field, according to the International code of botanical nomenclature 

 (Briquet, 1912) which stipulates that the first specific name applied to 

 the perfect stage must be used. If the American code be followed, the 

 specific name must be attributed to Persoon. He used it for the pycnidial 

 stage, which he called Sphaeria trifolii in 1801 (1801:30). Many years 

 after Persoon's original description, Kunze and Schmidt described the 

 hyphonrycetous stage as Polythrincium trifolii in Deutsche Schwaemme, 

 fascicle 5, page 5 n. 121, (Greville, 1826). In 1817 they republished the 

 description (1817:13). Fries (1829:368) attributes Polythrincium trifolii 

 to Kunze alone. 



Nothing of importance happened to the nomenclature of the fungus 

 until 1849 when Fries (1849:368) designated it Dothidea trifolii, based 

 on a supposed perfect stage. He does not give any description. Twenty 

 years later Fuckel (1869:218) placed the fungus in Phyllachora trifolii, 

 listing Polythrincium trifolii as the conidial synonym and the pycnidial 

 stage described as Sphaeria trifolii by Persoon as the spermogonial 

 synonym. He lists Dothidea trifolii of Fries as another synonym. 



When Saccardo (1883:613) listed the fungus, he designated it 

 Phyllachora trifolii (Pers.) Fckl., admitting all the while that the " status 

 ascophorus nondum repertus sed habitus omnino Phyllachorae," — a free 

 translation being that although the ascogenous stage had not yet been 

 discovered, the general appearance places it in Phyllachora. 



