HORTICULTURAL SOCIETY. 289 



showers followed by damp, close, muggy air with hot sunshine, 

 followed by more showers, etc., then the conditions are favorable 

 for the spores of this variety of mildew to germinate and take 

 lodgement, or literally to take root upon the under side of the 

 leaves. The varieties of grapes subject to this attack are those 

 whose leaves have a skin and structure delicate and sensitive; 

 those whose leaves have a tougher skin and structure are never 

 attacked except in the neighborhood of a large plot of a variety 

 very seriously affected, and even then no injury is done to them. 

 As a rule the Concord and all its seedlings are exempt from 

 this disease and all the other varieties planted in Minnesota 

 are more or less liable to it. When a block of any variety sus- 

 ceptible to it is attacked, it appears at once over the whole 

 block as though the spores has been dusted upon it at once from 

 an immense dredging box. It appears at first as fine white down 

 upon the under side of the leaves and if the attack is a mild one 

 it will be confined largely to the half grown leaves; if a severe 

 one all leaves are liable to be affected, except perhaps a few of 

 the very smallest. After the spores have found lodgment, they 

 instantly take root and sprout up, a miniature white forest. 

 It usually covers only a portion of the leaf and lies in spots, 

 which do not spread very much. As it grows the roots rapidly 

 permeate the interior of the leaf and eat up its substance. In a 

 few days the white appearance is succeeded by a yellowish tinge 

 and then changes to dark, followed by a drying of that portion of 

 the leaf affected; in many cases the leaves fall, at least their 

 ability to nurture the vine and ripen the fruit is seriously im- 

 paired, and the quality of the grape is greatly injured. 



Our climate is the great natural safeguard against this disease, 

 but among precautions which experience suggests as reasonable 

 to take against an attack, are locating the vineyard upon high, 

 well drained, yet good, soil, where there is a good circulation of 

 air; spreading the vines well out upon the trellis without crowd- 

 ing; a reasonable amount of summer pinching, not so much as 

 to entirely denude the vine of young leaves, but enough to ma- 

 ture a large number of healthy, well developed leaves; keeping 

 the vines up off the ground and cultivating well. A nursery of 

 young, growing vines is particularly susceptible to this disease, 

 and should not be located near a vineyard. With all these pre- 

 cautions in peculiarly unfavorable seasons the vineyard may not 

 escape, but all things being equal the chances will be better and 



Vol. IV— 37. 



