178 Atnericcui Gooseherrij-M'ddeiv 



A very similar case is that of the oak mildew. About 10 years ago 

 oak " scrub," and to some extent oak trees also, in England and in many 

 parts of the Continent, became for the first time attacked by a species 

 of the Erysiphaceae in the conidial stage. It received many names 

 {e.g. Oidium alphitoides, 0. querciniim, etc.) at the hands of mycologists 

 belonging to that class which has sufficient time only to add to synonymy. 

 In 1911, the discovery in France of the perithecial stage of this mildew 

 on some autumnal shoots of the oak, proved its identity with an endemic 

 American form of Mwrosphaera cilni (Wallr.) Salm., which occurs 

 commonly on species of Quercus in the United States. Here, again, 

 quite exceptional seasonal conditions would seem to be necessary for 

 the formation of the perithecial stage of this mildew when introduced — 

 as presumably has been the case — into Europe from America. No 

 perithecia have been found in this country and certainly as a general 

 rule the oak-mildew passes the winter in the conidial stage in a more 

 or less dormant condition. 



A third case is the mildew which attacks the foliage of that very 

 useful ornamental shrub Euonymvs japonicus. This mildew first 

 appeared in England, and also on the Continent, about 15 years ago, 

 and only the conidial stage is known i. It is possible that it is a form of 

 Erysiphe Polygoni endemic to Japan on Euonynms japoniciis, and that 

 it has been imported with that shrub from Japan into Europe. The 

 mildew exists in Europe during the winter months on the evergreen 

 leaves in dormant or nearly dormant hibernating mycelial patches, 

 which on the advent of a warm spell of weather soon produce conidia. 



What now are the facts with regard to the life-cycle of the American 

 gooseberry-mildew {S2ihaerofheca mors-vvae (Schwein.) Berk.) in this 

 country, since its introduction into Europe from America about 1900 ? 

 Has its normal life-cycle been interfered with in any way as the result 

 of new factors such as change of climate or different " constitutional " 

 characters of its host-plants ? There is, I think, some reason for thinking 

 that it has. There is no evidence that there is any hibernation of the 

 conidial stage. The perithecial stage — or at least the outward signs 

 of it — is formed abundantly on the surface of the young shoots of the 

 gooseberry. It has been assumed from the first — and quite rightly so 

 under the circumstances — that the continuance from year to year of 

 this new and most destructive pest was everywhere ensured by this 

 abundant production of the perithecial stage. Some facts which I have 



' Salmon, E. S. Fungus Disease of Euomjmus japonicus (Journ. Roy. Hort. Soc, xxix. 

 p. 4:U (l!t05)). 



