OH EUHGOID DISEASES OE THE VINE. 
73 
On Fungoid Diseases of the Yine. Part II. By Dr. M. C. Cooke. 
[Read at Meeting of Scientific Committee 19th February, 1877.] 
Ik following up the series of communications which were promised 
at the last meeting, it may be as well to allude at once to the 
American Peronospora as a sequel to the American Yine diseases 
noticed in the previous paper. As on that occasion, so in the pre¬ 
sent, we shall avail ourselves freely of the observations made on 
the spot by Dr. Farlow,' vl since they must necessarily have been 
made under much more favourable circumstances than it is possible 
to achieve for ourselves, since we are compelled to study it from 
dried specimens only. 
Peronospora viticola , Berk. & Curt., is confined solely to the 
United States, as far as we know, and there it attacks almost all 
the species or varieties of Yine. It makes its appearance about 
the 1st of August, and at any time from the middle of the month 
until frosty weather sets in, one can be almost certain of finding 
it- It developes first on the under surface of the leaves, most 
abundantly on the veins near the petioles, and afterwards on spots 
all over the under surface. It is most easily recognised on Vitis 
cordifolia , where the under surface of the leaves is smooth, and 
where the frost-like substance of the Fungus is in strong contrast 
with the green leaf on which it grows. When growing on Vitis 
Labrusca , Vitis eestivalis, or cultivated varieties of these species, it 
appears in the form of spots, at first white, then rusty, slightly 
raised above the level of the hairs of the lower surface. Some¬ 
times the Fungus invades the petioles of the younger leaves, which 
swell considerably beyond their usual dimensions. As the disease 
advances, the Fungus spreads over the whole of the lower surface 
of the leaves, until not unfrequently scarcely a healthy leaf 
remains; red spots appear, which expand until the leaf becomes 
dark-brown and shrivels up. During August the disease in the 
region of Boston advances gradually, until, towards the middle of 
September, almost every leaf is affected and hangs dead upon the 
branches. 
The mycelium is profuse throughout the cellular system of the 
leaf, and the fructifying threads force their way through the 
stomata, often several of them together, a portion of which seem to 
grow faster than the rest and become fertile. The erect threads 
* On the American Grape Yine Mildew, by W. G. Farlow, in Bulletin of 
the Bussey Institution. 
