DISEASE OF THE VINE. 237 



I have indeed observed upon other plants the true Erysiphe with 

 characters far too decided to confound it with this cryptogam of 

 the Vine. It is a beautiful object when seen through the micro- 

 scope with reflected light, when the field comprises a number of 

 conceptacles in different stages of maturity. Their brilliant 

 colours, which pass gradually from a pale yellow to orange, to red, 

 to dark blood-red, or almost to black, have a pleasing effect on the 

 white ground, formed by the filaments radiating from each of the 

 globose sessile fructifications. Every one of these fructifications 

 when detached carries with it, like a Medusa's head, its radiating 

 serpentine hair, and as the greater part of these filaments separate 

 from the entangled ground without laceration, that is, with their 

 extremities closed and convex, I conclude that these filaments 

 have no connection for the purpose of suction with the interior of 

 the plant, on which the Erysiphe fixes itself. I am rather dis 

 posed to consider them as aerial roots, or rather as fronds analo- 

 gous to those of lichens, an analogy which appears to me to 

 extend to other parts of the fructification. The oval spores of the 

 Erysiphe communis, from 4 to 8 in number, are contained in 

 extremely transparent utricles formed of a coai'se membrane of 

 - 045 millimetres in length, implanted on the conceptacles by a 

 connecting surface of 01 1 millimetres in diameter, not unlike the 

 asci of lichens. It is not my intention to enter into any more 

 circumstantial description of the Erysiphe, or of its mode of pro- 

 pagation. I have only incidentally mentioned its structure, in 

 order to show more clearly how very different it is from the cryp 

 togam of the Grape. :;: 



* Those who arc firmly convinced that the cryptogam of the Grape is an 

 Erysiphe, may perhaps maintain that the fructification I have described is 

 no more than a lower degree of development of the plant, and that if it 

 reached the same state of perfection it would show the characters peculiar 

 to the genus. 



It is not impossible indeed that such a thing may happen, but it is 

 highly improbable, for if we consult the works which treat of the Erysiphe, 

 and especially the fine memoir of M. Leveille inserted in the Annales des 

 Sciences Naturelles, we do not find, among all the species known and well 

 analysed, a single one which shows any change of structure, leading to any 

 suspicion of two modes of fructification so very different; the one being 

 represented by a pedunculated sporangium full of several hundreds of free 

 spores; the other by a conceptaculum, either sessile or only inserted on 

 several filaments, and containing a small number of large spores enclosed 

 in a very small number of sporangia. 



I consider, therefore, that my proposition, that the cryptogam of the 

 Grape is not an Erysiphe, is sufficiently proved, and I do not think that 

 the contrary opinion is admissible, until some instance has been authenti- 

 cated where the same mycelium will produce the three different degrees 



