294 OBSERVATIONS ON THE VINE MILDEW. 



the mildew ceasing after tiie disease had been established, as 

 mentioned by Dr. Leveille ; but the progress of the malady was 

 completely arrested, which would not probably have been the 

 case had the grapes suffered from some inherent corruption of 

 the tissues themselves.* And the experience of Mr. Boys is 

 borne out by tJie testimony of the great body of grape growers in 

 the south of England. As the sulphur is the well-ascertained 

 cure of the fungus to which peach mildew is due, it is only 

 natural to conclude that the cause is somewhat similar in grape 

 mildew, wiiere the effect is equally beneficial. Salt was not 

 found efficacious in England, and where sulphur is used, except 

 in the form of vapour, it must be used in substance, as it is inso- 

 luble in water. How it acts upon the mould is not known, but 

 doubtless some decomposition takes place, and where used in 

 combination with lime the sulphate of lime may act as a stimu- 

 lant to the vegetative powers. Possibly, a combination of quick 

 lime and CTlauber's salts, as recommended with such great benefit 

 in the case of Bunt, might be an improvement on the methods 

 hitherto practised. 



It is curious that the grape mildew has taken a course nearly 

 contrary to that of the potato disease. It appeared in Kent 

 about 1845, and is at this time prevalent on the opposite coast 

 of Essex, and has now extended southward as far as Naples. 

 At Genoa scarce a vine is free, and the black grapes appear to 

 be attacked quite as much as the white varieties, even the Vitis 

 Labrusca suffering from its ravages. In the north and midland 

 counties of England I believe the disease is unknown, and I 

 have not heard of its appearance in Germany. 



Where the mind can be brought to adopt the notion of spon- 

 taneous or equivocal generation, there is little difficulty in these 

 matters, or at least tlie difficulty is thrown aside ; but as all patient 

 investigation, and one which will not submit to jump hastily to 

 conclusions from imperfect data is against such notions, we nmst 

 be content to treat the propagation of even such minute bodies 

 as Oidium Tiickeri as we do those of phenogamous plants. 



* It is but fair that I should state that Mr. Boys does not attribute the 

 disease to the Oidium, but to some disturbance of the electric currents of the 

 earth — an opinion to which he has been led from constant observation of a 

 thermometer plunged 20 inches below the surface of the soil. The disease, 

 he states, first appeared with him in 184G, in remarkably fine and dry 

 weather, subsequent to a cold and wet spring. The roots of his vines, in 

 consequence of the drought, had been kept wet with liquid manure, the 

 temperature of the earth Ijeing comparatively low. In regard to the use of 

 remedies, he recommends cultivators to watch for the very first indications 

 of the white bloom which constitutes the Oidium, and then, in four or five 

 days, the cure is certain. A few days' neglect will require greater per- 

 severance in the use of the remedy ; but if the young grapes once split and 

 become deformed, it may possibly be too late to do any good. 



