OBSERVATIONS ON THE VINE MILDEW. 287 



that he recognised in this plant the Erineum vitis. Messieurs 

 Alphonse de Candolle and Duby opposed this view, because 

 they were well acquainted with the Erineum, and had made a 

 particular study of Torula dissiliens, M. Vallot is, to a certain 

 extent, excusable, because he had seen neither the new Torula 

 nor the figure which accompanies the memoir of M. Duby. But 

 the persistence of the Erineum, and the ease with which thy 

 Torula disappears, ought to have raised doubts in liis mind. 

 It is sufficient to blow strongly on tlie lower surface of the leaves 

 to cause it to fly away. So much is this the case that M. 

 Alph. de Candolle remarks, in a note, ' When I wished lately to 

 re-examine the Torula dissiliens preserved in my herbarium, I 

 found that the act of drying had caused almost all the joints 

 of this microscopic plant to fall. There remain only the dis- 

 eased leaves of the vine, marked with traces of the parasite, 

 and some very fine powder.' 



The Oidium Tuckeri is more easily preserved, and is not dis- 

 persed by a mere breath of air ; but it is, nevertheless, difficult 

 to recognise its character in dried specimens, beause the spores 

 separate with the greatest ease when it is dry, and nothing 

 but the mycelium is left behind, which resembles that of an 

 Erysiphe. 



The certainty which has been acquired of the spontaneous 

 development of moulds on some living animals, and especially 

 that of Botrytis Bassiana, or silkworms, has made people 

 believe, though wrongly, that many diseases of vegetables and 

 animals were due to a similar cause. Exaggeration has been 

 pushed a little too far. It is well known now, from the re- 

 searches of M. Decaisne, that the nematoid mycelium, which 

 we find under the epidermis of diseased potatoes, pears, and 

 rotten apples, &c., is consequent on disease in those productions. 

 It is the same with tlie Oidium of the grape. Mr. Berkeley in 

 England, and M. Duchartre in France, tliink that the mould is 

 the first cause, and the disease its consequence. The researches 

 which I have made do not allow me to participate in the 

 opinion of my honourable friends. M. Decaisne and myself have 

 made vain efforts to discover under the epidermis the least trace 

 of mycelium upon the grapes, the vine-leaves, and on the 

 branches, when beginning to be diseased. We have satisfied 

 ourselves that all the phases of tiie vegetation of tlie Oidium 

 take place on the surface. The tissues are affected first, and 

 when a white spot begins to appear, however minute it may 

 be, the mould is developed ; if the finger is simply passed over 

 it, it disappears ; and if we examine tlie spot with a lens, we 

 see at the point whicli it occupied and around it, where no 

 malady was suspected, extremely minute black or brown specks 



