152 A Monograph of the Erysiphaceae 



- Var. extensa (Cooke & Peck). [Fig. i8] 



M. extensa Cooke & Peck, Journ. of Bot. II. i: I2. 1872; 

 Peck, Reg. Rep. 25: 1873; Sacc. Syll. Fung, i: 13. 1882. 



M. qiicrcina (Schwein.) Burr. ; Burr. & Earle, Bull. III. State 

 Lab. Nat. Hist. 2: 424 (partim). 1887; Burr.; Ell. & Everh. 

 N. Amer. Pyren. 28 (partim). 1892. 



M. qiurcina (Schwein.) Burr., var. extensa Atkins. Jour. Elisha, 



Mitch. Sci. Soc. 7 : 72. 1891. 



Exsicc: Rab.-Wint. Fung. Eur. 5033; de Thuem., Myc. 



univ. 756 ; Kellerm. & Swingle, Kans. Fung. 11. 



Epiphyllous ; mycelium persistent, effused or forming irregu- 

 lar spots ; perithecia more or less densely gregarious, often forming 

 floccose patches 90-140 ii in diameter, averaging 115 /^ ; cells 



0-20 



% 



perithecium, rather delicate, flexuose, flaccid, narrow (about 5 ^« 

 wide), sonietimes slightly angularly bent, usually smooth, occasion- 

 ally rough at the base, colorless, aseptate, thin-walled throughout, 

 or rarely becoming thick-walled towards the base, apex 3—5 times 

 more or less closely dichotomously branched, tips of ultimate 

 branches regularly and distinctly recurved ; asci 3—8, ovate or 

 broadly ovate, shortly stalked, 58-72 x 34-45 /^ ; spores 4-8, 

 usually 6, large, 22-26 X 12-15 //, 



Hosts. — Qiicrciis alba^ Q, discolor, Q. nigra, Q. palnstris, Q. 

 mbra. 



Distribution. — North America : United States — Massachu- 

 setts, New York, Pennsylvania, New Jersey, North Carolina (9), In- 

 diana, Illinois, Wisconsin, Missouri, Kansas. 



The variety extensa differs from the type in the longer, narrower, 



flaccid appendages and slightly larger spores. The branching of 



the apex is not as a rule different from that of certain forms of 



M, alniy and is much closer and more elaborate than that of the 



var, vaccina. Cases occur, however, although rarely, in which 



the manner of branching of the apex is the same in these two 



plants ; the var. vaccinii can then be separated by its larger spores. 



The present plant was described as a species, J/, extensa, by 



Cooke & Peck, but there can be no doubt that it is too close to 



M. alni to be allowed this position. In its well-marked state the 



appendages are about 4}^ times the diameter of the perithecium, 



flaccid, and narrow, and so appear verj' different from the stouter 



