ON THE PERONOSPORiE. 201 



and 15th of June. In Massachusetts, on the contrary, it does not 

 show itself except in the autumn, and causes scarcely any hurt to 

 the vines. The following is Prof. Farlow's account of it : — " It 

 might naturally be supposed that a fungus so common as P. viti- 

 cola^ and so often found on all the leaves of the vine, must have 

 very disastrous effects on the crop. This is, however, not the 

 case. The fungus does not attack the grapes themselves. Be- 

 sides, at least in New England, it does not make its appearance 

 before August ist, and the leaves do not look brown until the 

 month of September. As regards the culture of vines in the 

 open air in the northern states, we are disposed to think there is 

 little to fear from the Peronospora, but that, on the contrary, this 

 fungus may be even beneficial. Our indigenous vines are very 

 luxuriant, and possess an abundance of leaves. That which is 

 most to be feared is, that in our short summers the grapes will not 

 be sufficiently exposed to the sun. The Peronospora arrives, we 

 think, at a time when the vines have attained their full growth, and 

 when the important point is, that the grapes covered by the leaves 

 should ripen. In drying up the leaves, the Perojiospora allows the 

 sun's rays to reach the grapes, and it does not seem to injure the 

 vines, which appear to grow on as usual.'' It is hoped that it may 

 be the same in Europe. 



P. ScHLEiDENiANA. Onion Peronospora. 



Fertile threads robust, erect, not septate, branched alternately ; 

 ultimate ramuli forked ; acrospores seated on tips of ultimate 

 ramuli, obovoid or nearly pear-shaped, attenuated at the base, 

 membrane of a dirty violet colour. The individual threads are 

 distinct, but form large patches on the leaves, or even entirely 

 cover them. This fungus is easily distinguished by the peculiar 

 shape of the acrospores. It is not confined to the onion, but 

 appears also on other allied species of Allium. It is very common 

 and destructive some years, preventing the plants which are 

 attacked from coming to perfection. It was described in the 

 Gardener's Chroiiicle for 1850 as causing great destruction amongst 

 the onions in Bath and the neighbourhood during that year. 

 Berkeley described this fungus in the Annals of Natural History 

 under the name of Botrytis destructor. 



