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other species of Ribes and Sambucus. The American gooseberry 
mildew is Sphaerotheca mors-uvae. M. grossulariae is seemingly 
quite rare in Iowa. 
5. Microsphaera diffusa , Cooke & Peck. 
Microsphaera diffusa Cooke & Peck. Bessey, The Erysiphei. 
Microsphaera symphoricarpi E. C. Howe. Bessey, The Erysiphei, and Prel. 
List, Ames Flora; Hitchcock; Partial List Iowa Powdery Mildews. 
Amphigenous; mycelium persistent or somewhat evanescent; perithecia scat- 
tered or gregarious, variable, 55-126 micra in diameter, cells 10-20 micra wide; 
appendages 4-30 or rarely more, l%-7 times the diameter of the perithecium, 
colorless or pale brown toward the base apex, 3-5 times dichotomously branched, 
tips not recurved, branches of the higher orders often appearing lateral; asci 
4-9, 46-60x28-30 micra, short pedicellate; spores 3-6, 18-22x9-11 micra. 
On Meibomia canadensis (L.) Kuntze. Decatur Co., Oct., 1904 and 1905 (An- 
derson) ; Fremont Co., Aug. 8, 1905 (Anderson) ; Ringgold Co., Oct. 7, 1905 
(Anderson) . 
On Meibomia sessilifolia (Torr.), Kuntze, Ames, Sept. 14, 1898. 
On Symphoricarpos symphoricarpos (L.) MacM. Ames, Sept. 7, 1882 (Bes- 
sey) ; Oct. 4, 1882 (Bessey) ; Aug., 1886 (Hitchcock) ; Decatur Co., Sept., 
1904 and 1905 (Anderson); Corydon, Nov. 5, 1900 (Stromsten) ; Fremont 
Co., Aug. 7, 1905 (Anderson); Johnson Co., Oct., 1882 (Hitchcock). 
The form on Meibomia has generally been considered distinct 
from that on Symphoricarpos but there does not appear to be suffi- 
cient difference to justify such separation. 
In the southern part of the state this species is very common both 
on Meibomia canadensis and Symphoricarpos vulgaris. In summer 
Symphoricarpos sometimes presents a whitish appearance from the 
abundance of the conidial stage of this species. 
6. Microsphaera russellii Clinton. 
Microsphaera russellii Clinton. Bessey, The Erysiphei and Prel. List Ames 
Flora; Hitchcock, Partial List Iowa Powdery Mildews; Fink, Blights, etc., 
of Fayette. 
Amphigenous; mycelium inconspicuous; perithecia scattered, 70-118 micra in 
diameter, cells 6-14 micra wide; appendages 5-14, 3-7 times the diameter of the 
perithecium, flaccid, colored nearly to the apex, septate, apex 2-4 times 
dichotomously branched, branching irregular and lax, tips not recurved; asci 
4-9, short pedicellate, 42-56x24-32 micra; spores 3-5, 18-22x10-12 micra. 
On Oxalis stricta, L. Ames, Oct. 17, 1878 (Bessey) ; Decorah, Oct. 19, 1878 
(Holway) ; Decatur Co., Oct., 1905 (Anderson) ; Fayette, Oct., 1892 (Fink) ; 
Iowa City, Oct., 1886 (Hitchcock). 
In this species the appendages are very slow in arriving at maturity. 
Microsphaera euphorbiae (Peck), Berk & Curt. 
Erysiphe euphorbiae Peck. Bessey, The Erysiphei. 
Microsphaera euphorbia (Peck), Berk & Curt. Fink, Blights, etc., of Fayette. 
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