84. A Monograph of the Erysiphaceae 



tliecia, the appendages in proportion to the diameter of the perithe- 

 cium are shorter, nearly always more or less crowded, and have a 

 small and closely uncinate apex ; the asci are usually 4-spored. In 

 the form of U. salicis occurring on species of Populns the perithecia 

 average smaller, the appendages are fewer — in rare cases as few 

 as 15 — longer, more flaccid, with the apex frequently more loosely 

 uncinate, and the asci are more often 6-spored. So many exam- 

 ples, however, on both Salix and Populns show characters inter- 

 mediate in every respect — for instance, it is not at all uncommon 

 to find forms on Populns in which the appendages are very crowded 

 — that, as already mentioned, the two forms cannot be considered 

 specifically distinct. We may, however, perhaps regard them as 

 incipient species which are being evolved on different host-plants. 



Levellle (214), Winter (394), Jaczewski (176), Saccardo (307), 

 and other authors have recorded U. salicis as growing on Bctula, 

 but I have not been able to find specimens on this host-plant in 

 any herbarium. It may be that perithecia (without appendages) 

 of Phyllactinia corylca — a species which occurs commonly on 

 Betnla — have been mistaken for immature examples of the present 

 species, and the same suggestion may be made with regard to 

 Wallroth's (383) record on U. salicis on Bnxns senipervircns. 



Leveille (214, p. 151) recorded Artemisia vulgaris as a host- 

 plant for U. salicis, and (I.e., p. 152) gave '' Alphitomorpha dcpressa 

 var. ^ artcmisiae Wallr." as a s}-nonym of the present species. 

 Leveille remarked, " J'ai regu beaucoup d'echantillons d'Erysiphes 

 sur I'Armoise sous le nom d' Erysiphe deprcssa, et pas un ne se 

 rapporte avec celui de Wallroth, que renferme I'herbier de M. 

 DeCandolle. C'est cette espece que je reunis a V Lhicimda adnnca 

 [6^. i-i?//m], parce qu'elle en presente tous les caractcres ; I'autre 

 est un Erysiphe propremcnt dit." In Berkeley's herbarium, at 

 Kew, there is a specimen from Leveille's herbarium, labelled in the 

 latter author's handwriting " Uncimda aduiica. Alphitouiorpha 

 deprcssa W^allr. ^. artcmisiae. Specim, Wallrothii." 



On this specimen (on the leaf of Artemisia vulgaris^ there are 

 two species, viz : Uuciiuda salicis and Erysiphe cichoriaccannn. Of 

 the former species, I found only two perithecia. These were quite 

 loose and merely entangled in the hairs of the leaf, and I feel no 

 hesitation in regarding their presence as accidental. Wallroth's 



