424 Illinois State Laboratory of Natural History. 



after all, this form may not be distinct. In the present state 

 of our knowledge, the classification of these minute plants is 

 necessarily based almost entirely on their morphological char- 

 acters; and as there are no constant differences of form by 

 which they can be distinguished, it is necessary to consider 

 them identical until the contrary is proved by a careful study 

 of their development and life history. 



M. quercina, (Schw.) Burrill. 

 (N. A. Fungi, p. 270.) 



Erysiphe quercinum, Schw. (N. A. Fungi, p. 270). 

 Microsphxra externa, C. & P. (Erysiphei of U. B., in Jour, of Bot., 1872). 

 Microsphxra abbreviata, Peck (28th Rep. N. Y. State Mus., p. 64). 



Ephiphyllous, 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 ^u, reticulations evi- 

 dent, small, and irregular; appendages less than 20, varying 

 in length from less than, to 4 or 5 times, the diameter of the 

 perithecium, hyaline, often tinted at base, smooth or some- 

 times roughened, usually regularly 5-6 times dichotomous, 

 branches 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 rup- 

 turing by slight pressure; spores 4-8, variable, usually large, 

 20-30 n long. 



M. extensa, C. & P. Mycelium thin, effuse, persistent; conceptacles 

 globose, black; appendages eight to twelve, in length three or four times 

 the diameter of conceptacle, colorless; sporangia four, subglobose or 

 ovate, containing four to six spores. Upper surface of oak leaves. Quer- 

 cus rubra.— Peck, 25th Rep. N. Y. State Mus., p. 95. 



M. abbreviata, Peck. Mycelium thin; conceptacles small; append- 

 ages six to fifteen, hyaline, rough, shorter than the diameter of the con- 

 ceptacles, many times dichotomous at the tips, the ultimate ramulre 

 curved; sporangia three or four, containing three to five, mostly four, 

 spores; spores large, .OOl'-.OOlS' long, 00060' broad. Under surface of 

 dead or languishing oak leaves. —Peck, 28th Rep. N. Y. State Mus., p. 64. 



On Quercus alba: Rock Island, Sept. 24, 1667; McLean, 

 Oct. 12, 1848^; Jo Daviess, Sept. 18, 5968; Jersey, Oct. 12, 

 6276; Jackson, Nov. 5, 2269; Union, Oct. 2, 6541, 6545, Oct. 4, 

 6565, 0,-t. 28, 2085, 2186, 2099J. Q. obtusiloba: Union, Oct. 2, 



