HORTICULTURAL JOURNAL. 213 



has since attributed them to the Oidiuni Tuckeri, of which he thinks they 

 are the most perfect organs of generation. I have myself seen the organs 

 in question on diseased Vines in the neighborhood of Paris. I have not 

 only seen them as other observers have, sometimes elongated, sometimes 

 globular, but I also perceived that among the globular there were some large 

 ones which were perfectly spherical and sessile on the byssus which produces 

 them. These observations have led me to conceive quite another idea of 

 the Oidium Tuckeri than that admitted by those authors, who, up to the 

 present time, have been considered as authorities on the subject. 



There is a sort of mildew common in our country which, in its first stage 

 is not in any way different from the fungus nourished by the diseased Vine. 

 The Erysiphes, as they are now called, present, for the most part, ovoid ter- 

 minal seeds, and also brown many-seeded conceptacles similar to those above 

 mentioned. By means of numerous observations, made principally on the 

 E. pannosa, Knautise, guttata, adunca, holosericea, Berberidis, Prunastri, 

 lamprocarpa, and Martii, I ascertained that the fruits in question assume 

 various forms in the same species of Erysiphe ; that they are cylindrical, 

 elongated, simple or two-celled, naked, or surmounted with beaded cells, 

 which are ovoid, roundish, or even perfectly spherical; that among the lat- 

 ter some are without any filiform appendages,. whilst others are furnished 

 with the same distinctive hairs as the thecigerous fruits, and resemble them 

 so much as not to be distinguishable by their external characters only. 



Many mycologists still doubt whether the ovoid seeds which cover with a 

 white dust the thread-like thallus, on which, at a later period, the ascopho- 

 rous conceptacles of the Erysiphe appear, do really belong to these fungi. 

 They believe that these seeds, and the white byssus wmich produces them, 

 constitute together a distinct and complete plant, a fertile Oidium, of which 

 the Erysiphe is only a parasite, or a subsequent companion. They main- 

 tain that fungi have only one set of reproductive organs ; but this opinion 

 is every day losing credit. 



Several very strong reasons are now opposed to Erysiphes being consid- 

 ered as parasites, or the usual companion of various kinds of Oidium. 



In the first place, the association of existence observed in the case of 

 Erysiphe and the so-called Oidium — for instance, between E, pannosa and 

 0. leuconium, and between E. graminis and 0. monilioides, &c. — is so con- 

 stant that it would imply a necessary relation between these minute plants; 

 so that if the Oidium is a different plant from Erysiphe, the latter must 

 certainly be a parasite on the former. Besides one cannot distinguish in 



