Parasitic Fungi of Illinois. 425 



6540, Oct. 27, 2064. Q. macrocarpa: La Salle, Sept, 17,1581; 

 Union, Oct. 21, 1917, Oct. 28, 2090, 2095, 2105. Q. Prinus: 

 Union (Earle). Q. imbricaria : Union, Nov. 1, 2190, 2191. 

 Q. (nigra ?): Union, Oct. 4, 6563, 6566, 6577, Oct. 28, 2099, 

 2100. Q. coccinea: Pulaski, Nov. 3, 2224, 2225, Nov. 4, 2241. 

 Q. tinctoria: Champaign, Nov. 9, 2376; Union, Oct. 4, 6569, 

 6568, (6104 ?). Q. rubra: McHenry, Aug. 20, 1202, Aug. 27, 

 1336, Aug. 31, 1390; La Salle, Sept/ 17, 1573, Sept. 20,6255; 

 Rock Island, Sept. 23, 1635; McLean, Oct. 12, 1848, Oct. 18, 

 1883, Aug. 1, 2368; Stephenson, Sept. 13, 5810; Jersey, Oct. 

 12, 6275; Union, Oct. 4, 6555, Oct. 25, 2022, Oct. 28, 2081, 

 2094. Nov. 1, 2192. 



This abundant species probably occurs on other kinds of 

 oak in this State besides those mentioned above. Although it 

 is exceedingly variable, specimens from the same host species, 

 even when collected in widely different localities, show a rather 

 surprising agreement in characteristics; and, if varying consid- 

 erably, it is within much narrower limits than when all the 

 forms occurring on oak are taken into consideration. Thus on 

 Quercus rubra the mycelium is confined to the upper surface of 

 the leaf, and the appendages are long, three or four times the 

 diameter, slender, and flexuous. The branches of the append- 

 ages are short, and regularly dichotomous. It was this form 

 that Cooke and Peck described as M. externa; and if any of 

 them were worthy of a separate name it would be this one. On 

 Q. alba the fungus develops on the under side of the leaf al- 

 most as often as on the upper side; the perithecia average larger 

 than on Q. rubra; and the appendages are distinctly shorter 

 and more rigid, only once and a half or twice as long as the 

 diameter, while the branching is broader and more irregular, 

 frequently being exceedingly ornate. If these forms stood alone 

 we should be justified in giving them different names, but spec- 

 imens on Q. macrocarpa, Q. tinctoria, etc., present many inter- 

 mediate forms. On Q. imbricaria, nigra, and coccinea, especially 

 when occupying the lower side of the leaf, the appendages are 

 very short, often less than the diameter of the perithecium. 

 This form is M. abbreviata, Peck. Some of our specimens 

 agree perfectly with his description, but others show so many 

 intermediate stages between this and the f orms^ with longer 



