tinctions based on such variable characteristics, and it becomes neces- 

 sary, as in other genera of the family, to combine these rather widely 

 varying forms. Aside from the number of asci and sporidia, the forms 

 included here do not, however, present any very wide variations. In 

 fact, the branching of the appendages, and the cellular structure of the 

 wall of the perithecium, are strikingly alike in all of them, specimens 

 on Juglans cinerea and J. nigra, are sometimes very different from 

 the type, having appendages less than the diameter of the perithecium. 

 But on these same hosts other forms imperceptibly grade into the 

 characteristic ones, leaving no room for specific distinction. 



The form on Syringa is usually known as M. Friesii, Lev., that 

 on Viburnum as M. Viburni, Howe, that on Plat anus as M. Plataui. 

 Howe, that on Nemopanthes as M. Nemopanthis, Peck, and that on 

 Euonymus as M. Euonyrni (DC.) or M. comata, Lev. Others are 

 mostly referred to M. penicillata. Lev. 



In several American lists and collections we find M. Lonicerce, 

 (DC.) or its synonym M. Dubyi, Lev. In Europe the fungus on 

 species of Lonicera is evidently quite distinct and is appropriately 

 named; but American specimens on our species of this genus of host 

 plants are certainly different. Whatever else we do with them, they 

 must not be confounded with European species on allied hosts. L T n- 

 fortunately, no opportunity has been available to examine collections 

 on foreign cultivated species of Lonicera. The parasite on American 

 honeysuckles, is M. Alni, as above described. 



M. quercina, (Scliw.) 



Erysiphe quercinum, Schw. Syn. N. Am. No. 2492. 



Microsphcera externa, C. & P. Erysiphei of U. S. in Journ. of Bot. 1872. 

 Microsphcera abbreviata, Peck, 28th Rep. N. Y. State Mus. p. 64. 

 Microsphcera quercina, Burrill, Bull. 111. State J y ab. Nat. Hist. II, p. 324. 



Epiphyllous, hypophyllous, or amphigenous. Mycelium abundant, 

 rather thin and pruinose, forming orbicular patches or spreading over 

 the whole surface of the leaf. Perithecia abundant, scattered, varying 

 from 80-140 p, reticulations evident, small and irregular; appendages 

 less than 20, varying in length from less than, to 4 or 5 times the 

 diameter of the perithecium, tinted at base, smooth or sometimes 

 roughened, usually regularly 5-6 times dichotomous, branches usually 

 short and tips strongly recurved, but presenting many curious and 

 ornate variations caused by the more extended or unequal growth of 

 some of the branches. Asci 3-8, often rupturing by slight pressure". 

 Sporidia 4-8, variable, usually large, 20-30 p long. 



On Quercus alba, Q. stellata, Q. macrocarpa, Q. lyrata, Q. bi- 

 color, Q. PrinuSj Q. rubra, Q. ilicifolia, Q. coccinea, Q. coccinea var. 

 tinctoria, Q. palustris, Q.falcata, Q. Catesbcei, Q. aquatica, Q. nigra. 

 Q. imbricaria, Q. robur. 



