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IOWA ACADEMY OF SCIENCE 
ping thereby greatly weakening the vitality of the tree. On Prunus 
cerasus the perithecia usually occur on the under side of the leaf, 
while on the other hosts they are often found on the upper surface. 
2. Podosphaera leucotricha (Ell. & Ever.), Salmon. 
Sphaerotheca mali Burr. Fink, Blights, etc., of Fayette. Pammel, Powdery 
Mildew of the Apple, Cont. Bot. Dept. I. S. C., Iowa Acad. Sci., VII, 1899. 
Mycelium, on the young stem petiole, and leaves, persistent, thin, effused; 
perithecia densely gregarious, rarely scattered, 75-90 micra in diameter, cells 
10-16 micra wide; appendages of two kinds; apical appendages 3-11, 4-7 times 
the diameter of the perithecium, becoming thick walled, dark brown in the 
lower half, paler toward the tip, apex undivided or blunt, rarely once or twice 
dichotomously forked; basal appendages short, tortuous, pale brown; simple 
or irregularly branched; ascus 55-70x44-50 micra; spores 22-26x12-14 micra. 
On Malus malus (L.) Britt. Ames, *July, 1894 (Pammel) ; Sept. 4, 1894 
(Combs); Oct., 1894 (Carver); Fayette, Oct., 1893 (Fink). 
This species often attacks young seedlings in the nursery and at 
times does considerable damage. It is generally classed as a Sphae- 
rotheca but we feel inclined to agree with Mr. Salmon in placing it 
here. The appendages certainly show characteristics of both genera 
but the rigid apical appendages are certainly very unlike the ap- 
pendages in Sphaerotheca. The occasional forking of the tips of 
the appendages certainly indicate that it is a Podosphaera. 
Erysiphe, Hedw. f. 
Perithecium containing several asci, each ascus 2-8 spored; appendages, 
threads similar to the mycelium and often interwoven with it. The ap- 
pendages are rarely bosolete, or in the European E. tortilis, brown, assurgent 
and fasciculate. 
Key to Iowa Species of Erysiphe. 
Asci, 2-spored. 
Perithecia, large, 35-240 micra in diameter, becoming pizzoid...5. E. taurica 
Perithecia, 80-140 micra in diameter. 
Haustoria lobed 3. E. galeopsidis 
Haustoria, not lobed 2. E. cichoracearum 
Asci, 3-8 spored. 
Perithecia, 5-180 micra in diameter, usually about 90 micra 1. E. polygoni 
Perithecia, 130-280 micra in diameter, usually 180-200 micra. . . .4. E. graminis 
Erysiphe polygoni , DC. 
See Plate III. 
Erysiphe communis (Wallr.), Fr. Bessey, The Erysiphei, and Prel. List Ames 
Flora. Fink, Blight, etc., of Fayette. 
