1911-1912.] Notes on Parasitic A scoinycetes. — //. 435 



wound-parasites. i\^. solani Keinke & Berthold is associated 

 with the destructive winter-rot of stored potatoes, and N. 

 ditissima Tul. with the canker of apple-trees. 



The genus Polystigma is represented by P. rubrum (Pers.) 

 DC. and P. fulvicm DC. The former occurs on the sloe and 

 various other members of the genus Prunus. It forms on the 

 leaves, particularly on their lower surface, a fleshy stroma 

 rather thicker than the substance of the leaf, and of an 

 orange-red colour. In its earlier stage of development the 

 stroma contains numerous globose conceptacles, in which are 

 produced conidia of a filiform shape, slightly curved and 

 thickened at one end. After the leaves have fallen the 

 mature perithecia are developed on the stroma. The spores 

 are elliptical, obtuse, and hyaline. P. fulvum forms similar 

 stromata of a tawny colour on living leaves of bird cherry 

 {Prunus Padus). 



In Phyllachora are included several common parasites of 

 wild plants. In this genus the stroma is irregularly e£fused, 

 and consists of prominent, black, rounded excrescences, in 

 which the perithecia are embedded. The spores are hyaline, 

 and usually of an ovate or elliptical shape. One of the most 

 common species is Ph. ulmi (Duv.) Tckl., which, in its early 

 stage of development, is sometimes so abundant on the foliage 

 of elms as to affect almost every leaf on the tree. It produces 

 small brownish spots, and the spores are exuded copiously 

 from these in the form of whitish tendrils which become 

 effused over the surface of the leaf. The spores are com- 

 paratively large, fusoid-cylindrical, and divided into four cells. 

 As the season advances, the fungus on the elm-leaves enters 

 upon a second stage, formerly described as a separate species 

 under the name of Piggotia astroidea B. & Br. Small 

 blackish crusts, consisting of minute flattened tubercles 

 clustered together, are formed under the epiderm, and finally 

 burst through in a somewhat stellate fashion. Their spores 

 are oblong, truncate at the base, and rounded at the apex. 

 The perfect asci and spores of Ph. ulmi are matured after the 

 affected leaf has fallen to the ground in autumn. Other 

 common species of Phyllachora are Ph. junci (Fr.) Fckl., on 

 culms of Juncus communis; and Ph. graminis (Pers.) Fcki.-, 

 on living leaves of Dactylis and various other grasses, where 



