118 MONTAGNE ON 



Here then the connection is so clear between cause and effect, 

 between the agency of the fungus and the disease of the plants, 

 that the opposite view, which is not confirmed by a single positive 

 fact, appears to me to be flatly contradicted." Such are the 

 expressions of Mohl. When I come to the question of the proper 

 treatment and prevention of the malady, T shall have some new 

 arguments to bring forward in support of this opinion. 



Since it is abandoned now by everybody, even by some of the 

 authors who first pronounced in its favour, I shall leave in the 

 deep oblivion, from which it ought never to have been rescued, 

 that opinion which would refer all the serious phenomena which 

 attend the grape mildew to the presence of a species of Acarus. 



The popular and absurd notion, again, can only be mentioned 

 to be deplored, which ascribes the malady to the deleterious 

 influence of street gas and the steam of locomotives. This foolish 

 notion, participated by some who do not belong to the inferior 

 ranks of society, is no less diffused in Italy than in many of our 

 provinces. 



I cannot, however, omit mentioning a theory proposed by 

 M. Oudart, a clever and experienced cultivator of vines. It was 

 presented by him to the Royal Agricultural Society of Turin, and 

 it is to the report of M. Bertola that I am indebted for my know- 

 ledge. The author of this theory, resting on numerous observa- 

 tions made during a long tour through the vine districts, refers 

 the cause to atmospheric changes and influences. He attributes 

 the adherence of the Oidium to the berries, branches, and under- 

 surface of the leaves to the exudation of a viscid moisture which 

 commences by retaining the parasite, and as it hardens by 

 obstructing the stomates and pores of the plant. The variations 

 of temperatui'e also play a prominent part in this theory, from 

 which, if I mistake not, that which M. Guerin-Meneville has just 

 propounded differs but slightly. 



Oidium Tuckeri.^' — The description and figures of the Oidium 

 of the Vine have been so frequently reproduced that it seems 

 useless to dwell longer upon it. Nevertheless, as neither Mr. 

 Berkeley nor myself were acquainted with the important form of 



* The vine mildew is now so well known by this name that there would 

 he some inconvenience in changing it, even in order to adopt one more 

 conformable to the ideas which have been recently propounded as to the 

 real nature and position which this production ought to occupy in the 

 system of Mycology. 1 shall continue then to use the name in preference 

 to that of Erysiphe Tuckei-i. 



