422 BULLETIN OF THE BUSSEY INSTITUTION. 
occur on the varieties of V. vinifera growing in this country. As we 
have not had an opportunity in this region of examining such varieties 
growing in the open air, we cannot controvert this point; but our ex- 
periments prove that it can be made to grow on V. vinifera even more 
luxuriantly than on American species. 
To study the propagation of the disease, leaves of different species 
were kept under moistened ‘bell-glasses, and conidia were sown on 
them in different positions. The quickest method of infection was by 
laying a healthy leaf upon one affected with the fungus. In two cases, 
the fungus appeared on the healthy leaf at the end of the second day. 
It made no difference whether the upper or lower surface of the 
healthy leaf was brought in contact with the infected leaf, as far as 
the contagion was concerned. Again: germinating zodspores were 
sown on the upper and lower surfaces of healthy leaves of Vitis vint- 
fera, and of smooth-leaved American species. The fungus appeared 
first on the leaves of V. vinifera, on the fifth day after sowing, and grew 
luxuriantly, soon covering the leaves. On American species, it made 
its appearance a day or two later. Where the zodspores were sown on 
the leaf, the best results were obtained when sown on the lower sur- 
face. This is, perhaps, owing to the fact that the under surface of the 
leaves is concave, and readily holds the water used in the cultures, 
while the upper surface is somewhat convex. 
In order to find out in what way the hyphe produced from the 
zoodspores make their way into the vine, small slices of petioles were 
placed on moistened slides, on which were germinating conidia. In 
only one case was a direct result obtained; and then the germinal 
thread passed through the epidermis, and not through a stoma. On 
this point, however, our experiments were not sufficiently numerous to 
prove satisfactory. 
One would naturally suppose that a fungus so common as Perono- 
spora viticola, which often is found on every leaf of a vine, would have . 
an injurious effect upon the grape crop. Such, however, is not the 
case. The fungus does not attack the grapes themselves; nor does it, 
at least in New England, appear until about the first of August; and 
its withering effect upon the leaves is not very evident before Septem- 
ber. As far as out-of-door grape culture in the Northern States 
is concerned, we are inclined to believe, that, practically no harm is 
done by Peronospora viticola, but that, on the contrary, the fungus 
