158 A Monograph of the Erysiphaceae 



& Everh. Fung. Columb. 315; *Erikss. Fung. par. scand. 142; 

 *Krieg. Fung, saxon. 725. 



Epiphyllous or amphigenous ; mycelium evanescent, or sub- 

 persistent, thin and effused on the upper surface of the leaf; peri- 

 thecia scattered to densely gregarious, globose-depressed, very 

 variable in size, 65-130 {i in diameter, cells 14-20 /^ wide ; ap'- 

 pendages 5-23, i-i^4 times the diameter of the perithecium, 

 colorless, smooth, aseptate, thin-walled above, becoming thick- 

 wallcd in the lower half, when mature, apex 4-5 times closely and 

 regularly dichotomously branched, branches of the first and second 

 orders very short, all the segments deeply divided (giving a some- 

 what_ digitate appearance to the whole 'apex), ultimate branches 

 forming a narrow fork, tips not recurved; asci 4-10, broadly 

 ovate or oblong, usually with a very short stalk, 46-62 x 2^- 



38//; spores 4-6, very rarely only 3, variable in size, 20-28 x 

 12-16/^. 



Hosts.— Ribes floridtcmiG), R. Grossidaria, R. nigntm {6), R. 

 rotundifoliimi (6), R. sanguinciim, Sambucns Canadensis, S. race- 

 mosa and var. pubcscens. 



Distribution.— Eu^OFY. : Britain, France, Belgium, Netherlands 

 (263), Germany, Switzerland, Austria-Hungary, Denmark, Sweden, 

 Finland (196), Russia. 



Asia : Japan. 



North America: United States— Vermont, Massachusetts, 

 New York, Pennsylvania, West Virginia (249). North Carolina 

 (13), Ohio, Indiana, Alabama (12), Illinois, Wisconsin, Missouri, 

 Kansas (386), Montana (6), CaHfornia (159). 



A well-marked species in the deeply divided segments of the 

 appendages. The branches of the first and second orders are very 

 short, so that the divisions of the segments reach nearly to the 

 center, giving a somewhat digitate and very characteristic appear- 

 ance to the whole apex (see Figs. 34, 35). 



The American M. Van-Bnintiana (on Sanibucus Canadaisis) is 

 identical with the present species, although in the original descrip- 

 tion the branches of the appendages are described as " truncate at 

 their apices." When mature, however (Fig. 43), the branches 

 are bifid in just the same manner as in M. grossidariae, and the 

 original description was no doubt taken from an immature appen- 

 dage, such as is shown at Fig. 7^6, drawn from an American 

 specimen. 



