ORIGINAL COMxAI[JNICATIONS. 



V. — Botanical Notes on the Mildew of the Vine and 

 Hop. By the Rev. M. J. Berkeley, M.A.. F.L.S. 



The genus Oidium, a name, at the present moment, far too 

 familiar in every country where the Vine forms an important 

 object of cultivation, contains a heterogeneous mass of species 

 of very various affinity, agreeing only in the circumstance of the 

 spores, or sometimes merely of the component cells of certain 

 threads of the mycelium being arranged end to end so as to form 

 little necklaces. Amongst these there is a peculiar group con- 

 sisting of such species as O. leucoconium, Tuckeri, &c., distin- 

 guished by their mealy appearance, though not constantly of a 

 pure white, and developed on the green parts of vegetables. In 

 many cases this mycelium creeps amongst the large inter- 

 cellular spaces of the under surface of leaves, the moniliferous 

 threads making their appearance through the stomata; but this 

 is by no means constant or essential, for, as in the grape mildew, 

 though often exhibiting such a mode of growth, they are produced 

 with equal luxuriance on parts of the plant where there are either 

 very few or no stomata. 



Another circumstance connected with such species is, that in a 

 variety of cases they are the certain forerunners of different species 

 of Erysiphe. There are, indeed, some of these species which have 

 never been observed to be accompanied or succeeded by an Ery- 

 siphe, and it is possible that such may be autonomous, but in the 

 majority of instances, of which the hop mildew is an example, the 

 Erysiphe most certainly and constantly follows or attends the 

 Oidium. 



Under such circumstances it was natural that a question should 

 arise as to the character of this connection, and accordingly it 

 has been warmly contended on the one hand that the Oidium and 

 Erysiphe are perfectly independent, while on the other the Oidium 

 is regarded as the mere mycelium of the Erysiphe, and it has even 

 been hinted, though without any sufficient grounds, that the decidu- 

 ous joints of its erect threads may possibly be of sexual importance. 

 Asa step towards the solution of this question, some observations. 



