.4" 



188 A Monograph of the Erysiphaceae 



4 



free from the mycelium than is usually the case, and, as the peri- 

 thecia are often densely gregarious, give a slightly floccose appear- 

 ance to the leaf. This habit (which is found in some species of 

 Microsphacrd), however, is not confined to the plant on Caragana 

 and Cohitea, as in the forms of E. polygoiii on Lnpinns (European 

 and American) exactly the same appearance is found. 



pol) 



on 



M 



Parnassia Caroliniana. I have seen two specimens of this, one from 

 Madison, Wisconsin (Halsted and Tracy, August, 1893), ex herb. 



Tracy (in the Herbarium of the Missouri Bot. Garden), 

 where the fungus is labelled " Erjsiphe spatulata''\ the other from 

 Syracuse, New York (L. M. Underwood, July, 1899), named 

 Erysiphe communis. The striking feature of this form is the pres- 

 ence of few, brown, usually short, stout, rigid appendages. The 

 perithecia are 70-85 //in diameter, the asci 3-6, 50-58 x 30-36 n, 

 spores 3-5, very rarely 2, 20 x 10 /i. Except in the appendages, 

 the fungus agrees well with certain common forms of E. potygoni. 

 In the Wisconsin specimen the appendages give a very distinct ap- 

 pearance to the form ; they are usually few and very short, in fact 

 often rudimentary and only about a quarter of the diameter of the 

 perithecium in length, very stout (about 10 tx wide), and dark 

 brown throughout ; in the New York specimens, however, most 

 of the perithecia have longer appendages, 3-4 times, or more, the 

 diameter of the appendages, paler towards the apex, and j-Z 

 it wide, and it is then at once seen that the present plant is closely 

 connected with many forms of E. polygoni on various host-plants, 

 e. g., some specimens on species of Clematis and on Caragana 

 arborcscens are very similar. On the whole, I am inclined to re- 

 gard the fungus on Parnassia rather as a starved form of E. poly- 

 goni, caused perhaps by growing on an unsuitable host-plant 

 than as a true variety. 



(Since the above remarks were written, Halsted (157*) has 

 founded a new genus, Erysiphopsis, on this fungus on Parnassia 

 Caroliniana. I am quite unable to follow this treatment. Any 

 one at all acquainted with the forms of Erysiphe polygoni will, I 

 think, at once admit that the fungus in question clearly belongs to 

 the genus Erysiphe, and is, moreover, I believe, so close to certain 

 forms of this species that (as mentioned above) it seems doubtful 

 if it can be separated even as a variety. ) 



