64 A Monograph of the Erysiphaceae 



thecia which here and there form black masses on the stem, and 

 the rudimentary appendages. After a careful examination of the 

 specimens sent I am quite unable to separate the fungus from 5. 

 humuU^ and feel convinced that it is only one of the many forms 

 of this species, and that the slight characteristics which it presents 

 (which are not, however, confined to the fungus on SJicphcrdid) may 

 be regarded as probably due in this case, to the position of the 

 fungus among the densely arranged peltate scales of the stem of 

 the host-plant. Griffiths (151) records S. humuli, var. fuliginea 

 on ShepJicrdia argentea and vS". Canadensis^ and Burrill (60) the 

 same on vS, argentea ; probably in both cases the fungus is the 

 one above referred to 5. hiiuudi. 



Except in America, 5*. hiumdi has not hitherto been distin- 

 guished from the var. fnliginca, and the European host-plants, as 

 far as I have been able to see specimens of the fungus on them, 

 are here for the first time separated under the two forms. The 

 fungus recorded on host-plants which I have not s^^x\ I have been 

 obliged to leave under the aggregate species, '' S, Castagnei Lev/' 

 Many of these hosts, e. g.y species oi Epilobiuui, PotentUla^ etc., might 

 probably be safely considered those of ^. Jiuinidi ; others, e. g.y 

 species of Senecio, hnpatiens, Balsamina^ etc., as belonging to 

 the var. fidiginea. 



Although so many authors have referred the fungus on Cn- 

 cnrbita and Cucuvns to '* .5". Castagnei^' it seems very probable 

 that a mistake has been made in the identification, and that the 

 fungus in question is an Eiysiplie, In the first place, although 

 one finds in herbaria very numerous examples of a fungus in the 

 conidial {Oidiitni) stage on leaves of Cn ctn'bita diwd Cucnnns referred 

 to S. Castagnei^ in my experience no specimens in the perithecial 

 stage are to be found in herbaria on these hosts. It is evident, 

 therefore, that for some reason it has been the practice among 

 mycologists to name any Oidinni on Qieurbita and Cnciimis^ S. 

 Castagnei Lev. There can be no doubt also that this fungus on 

 cucurbitaceous plants is extremely slow in producing perithecia, 

 and the only example I have seen in this condition was gathered 

 in the late summer at Reigate, England, in 1898. This, as already 

 mentioned, proved to be Erysiphc cichoracearum. 



The practice of referring a fungus In its Oidinm stage to a 



