150 A Monograph of the Erysiphaceae 



Vaccinmin Canadense, V. Myrtilliis, \^ars. inacrophyllum and viicro- 

 phylluvi (\^\)^ V. Pennsylvaniaim^ V, vacillaiis. 



Distribution, — North America : United States — New Hamp- 

 shire, Massachusetts, Connecticut, New York, New Jersey, Mary- 

 land, West Virginia, (249) North CaroHna, Ohio, Michigan, In- 

 diana, Alabama, Illinois, Wisconsin, IMissouri, Iowa, Wyoming. 

 Canada — Ontario. 



The present plant is extremely variable in nearly all its char- 

 acters. 



Schweinitz, in 1834, first described the plant as growing on 

 Vacciniiun Pennsylvaniann, as Erysiphe vaccinii ; in 1872 Cooke 

 & Peck described a plant on Vaccinium vacillans as Microsphaera 

 vaccina^ giving E. vaccinii Schwein. (partly) as a synonym. 



Burrill has maintained M. vaccinii (Schwein.) Cooke & Peck 

 as a species, and has described the appendages as *'6-2o, hyaline, 

 smooth, slightly colored at base, 2 or 3 to as many as 6 times the 

 diameter of the perithecium, branching various, usually 3 or 4 

 times forked, with the tips truncate or bifid, not recurved, occa- 

 sionally more ornate, with tip distinctly recurved. This is a vari- 

 able species not only in the character of the mycelium, but in the 

 length and branching of the appendages. In most cases the tips 

 are swollen and not at all recurved.'' 



I am indebted to Professor Earle, Professor Ellis, Professor 

 Underwood, and other American botanists for numerous speci- 

 mens of the American forms of Microsphaera on Vacciniiun and 

 Epigiica. 



In the first place, it is evident, from the study of these, that it 

 IS incorrect to consider, as has been hitherto done in America, all 

 the forms that grow on species of Vaccinium as belonginjr to 



*' M. vaccina:'' On E. corymbosiun the only fungus that I have 

 seen is certainly to be referred to M. alni type ; this is, no doubt, 

 the plant recorded by Cooke & Peck (90, p. 12) as '' M. Fricsii 

 Lev. var. vaccinii" 



On other species of Vacciniiun, however, and on Epigaca, the 

 fungus differs from M. alni in having long, very flaccid, thinner 

 appendages, with the apical branching much more variable. Bur- 

 rill's description of the tips of the ultimate branches as " truncate 



or bifid, not recurved" undoubtedly refers to the immature condi- 

 tion only. 



