280 NINETEENTH REPORT. 



light brown. Toward the center the dark rings form ridges and are 

 narrow, while towards the margin they are broad and not raised. The 

 color contrasts between the two outermost rings is very sharp. Conid- 

 iophores and spores usually appear first on the under side of the leaf, 

 and can be seen with a hand lens as tiny black clusters, densest nearest 

 the center of the spot. Spores on the upper side of the spot may appear 

 simultaneously with those on the lower side, or later. The spots are 

 oval or round, and after seven days attain the size of 4-7 mm. x 3-5 mm. 

 The lesions, if isolated, may increase in size, the maximum noted being 

 13x8 mm. (Plate XII.) 



The spots resemble in general other Macrosporium or Alternaria leaf 

 spots. They are easily distinguished from the spots caused by Pseudo- 

 peziza trifolii, which do not have well-marked concentric rings. The 

 characteristic central apothecium also characterizes the Pseudopeziza 

 trifolii spot. In the early stages of infection, however, it is difficult to 

 distinguish between them. 



Spots seem to be most frequent toward the edge of the leaf. Those 

 adjacent to each other soon run together and the death of tlie tissue 

 lying beyond them follows. This is especially true when the attack is 

 near the edge of the leaf (Plate XIII, Fig. 8). Sometimes a large area 

 is completely covered with small spots which run together (Plate XIII, 

 Fig. 10a). The spots become dry and brittle with age and eventually 

 cause the death and drying out of the entire leaf. If the weather is 

 dry such leaves may hang on for a few days and then fall to the ground. 

 During wet weather they cling to the plant and in the case of the lower 

 leaves, the petioles droop and the leaves soon rot in the wet soil. 



Oil flic petioles: 



All attack on the petiole is very uncommon, and it sctms to be restricted 

 to those which are young and succulent. Upon them the fungus appears 

 in the form of dark brown to black linear streaks, one to three mm. long. 

 Little black clusters of spores may be seen on the surface of these streaks 

 (Plate XIII, Fig. 12). A type of petiole infection which results from 

 spores from the leaves is described on page 286 (Plate XIII, Fig. 9a). 



ETIOLOGY. 



Formal Proof of Pathogenicity of Macrosporium sarcinaeforme: 



Macrosporium sarci?iaeforme was isolated from the typical leaf spots 

 several times during the course of this study. In fulfilling Koch's rules 

 of proof, the fungus from one of these isolations was inoculated into 

 red clover leaves, and reisolated from one of the resulting diseased spots. 

 The fungus from the second isolation was sprayed upon another plant, 



