10 ON VI NK iMlLOEW. 



four branches are given off in a radiating manner, like runners, 

 wliich in tui'n develop new processes and a similar ramification ; 

 so that in this way the reticulate mode of branching and the quick 

 development of the Mycelium is connected with that of the 

 processes. A glance at Figs. 1, 3 proves that the mode of ramifica- 

 tion is very different, observing a different law, and in no degree 

 connected with the situation of the processes. 



That the extension of the fungus during summer (independent 

 of the immediate growth of the Mycelium) is ascribable to the 

 dispersion and subsequent ready germination of the oval utricles, 

 seems beyond all doubt. On the contrary, I was unable to dis- 

 cover where they are deposited through the winter, in what con- 

 dition they are, and how the first development of the plant takes 

 place in spring. One would imagine a priori, that they pass the 

 winter on the bark of the last year's shoots, or more especially on 

 the buds, and so when they expand are ready to germinate on 

 the young branches. I have, however, no express observations 

 on these points; only thus much is certain, that, as was before 

 remarked, the disease commences on the inferior internodes. 

 Whether the spores retain their form, or it is the already de- 

 veloped Mycelium which endures the severity of winter, is a point 

 worthy of further investigation. In this respect the new fruit 

 discovered by Amici is of the highest importance. He found, 

 in October, 1851, that individuals of the oval utricles of Oidium 

 Tuckeri enlarge, assume a yellow tint, acquire a cellular structure, 

 and contain hundreds of extremely small elliptic somewhat curved 

 spores, furnished with a little nucleus at either extremity. It is 

 possible that these spores, developed late in the autumn, live 

 through the winter, and in the following spring give rise to the 

 new invasion of the fungus. The investigation of this matter is 

 attended with no little difficulty on account of the extreme 

 smallness of the spores. In September, 1851, I did not find this 

 form of fruit in Switzerland, whether in consequence of the season 

 not being sufficiently advanced, or that it is produced only in 

 southern climes, points which must be decided by fresh observa- 

 tions. Cesati found similar fruit in Piedmont, on Oidium Tuckeri, 

 and I have just seen it in Bozen on an allied species, on tlie leaves 

 of hops, whereas Amici was led to its discovery in the vine, from 

 the investigation of an Oidium on the common gourd with the 

 same kind of fruit. Should further investigation afford any key 

 to this difficulty, I shall not fail to return to the subject. 



Bozen, June 2Qlh, 1853. 



