134 ON GRAPE MILDEW. 



with the diseased vine shoots on the same wall. Wiiether the 

 plant is capable of attacking' American vines I am not able to 

 say, since in the only vineyard in which I saw a quantity of 

 these vines, all were healthy, a circumstance which may, how- 

 ever, be accidental, since the vineyard itself was only slightly 

 infested wi(h the disease. 



As in so many other cases of fungi which accompany disease, 

 so in tlie grape mildew, the question has arisen wiiether the 

 fungus is the cause or the consequence of the malady ; and so, 

 also, as in many analogous cases, the original ground of the 

 evil has been attributed to insects, as, for instance, by Robineau- 

 Desvoidy (Conip. Rend, xxxiii. p, 343). This latter view seems 

 to me to be decidedly wrong. I am very far from wishing to 

 intimate that Robineau's observation of the presence of an 

 Acm'its on diseased vines is false, though, after the most careful 

 microscopical observations of many diseased vines, in all stages 

 of the malady, and in different places, I have been unable to 

 detect any insect, and therefore can only attribute their occur- 

 rence, as observed by M. Robineau, to mere accident. 



A far more difficult question to answer is that, wiiether the 

 fungus is the cause or consequence of the disease. Were the 

 fimgus an entophyte, did it arise from a visible demonstrable 

 alteration of the contents of the cells, did it break out from 

 within the plant to its external surface, the latter position might 

 be considered as proved.* Tlie contrary, however, of all these 

 things is the case. Not the slightest trace can be discovered of 

 any disease of the vine anterior to the appearance of the fungus, 

 which creeps over the cuticle of the plant, does not protrude 

 into its tissues, and much lessf arises within previous to 

 bursting forth into the free air. These circumstances make it 

 probable that the fungus first affects the plant on which it grows 

 by decomposing the juices of the superficial cells, and impeding 

 their growth in the same way in which Achlya proUfera injures 

 the aquatic animals on which it grows, and as Merulius destruc- 



* Oldinm leucoconium is an entophyte, exactly as Botrytis infestans and 

 the group of allied species which grow on green leaves ai-e eutophytes. The 

 probability therefore is pritnu facie that O. Tuckeri is an entophyte. — 

 yyansl. 



t It is figured in the ' Gardener's Chronicle ' as making its way, like 

 other Oidia, through the stomata. Le'veillc, however, like Mohl, denies that 

 this is the case ; and Duchartre asserts truly tliat there are no stomata (or 

 at least extremely few) on the upper surface of the vine leaves, on M'hich 

 the fungus grows according to Continental authorities. At Margate, how- 

 ever, it was more abundant on tlie under than on the upper surface of the 

 leaves. A re-examination of the matter must be deferred to the summer, as 

 it is impossible to make out anything satisfactory from dried specimens. 

 Indeed, like many other moulds, it is very diflBcult to preserve in the Herba- 

 rium, on account of the ravages of mites. — Transl. 



