DISEASES. 209 



attaches itself to living plants and draws its nourishment 

 therefrom ; and though generally found upon living bodies, 

 still it attacks only those that are feeble, as these either 

 have not sufficient strength to repel it, or the very weak- 

 ness of the plant gives it a welcome. 



The mildew is usually found upon the leaves of the grape ; 

 when it first appears it is but a single small white speck, 

 but it is soon surrounded by others, and by their rapid 

 multiplication they extend over the surface. These minute 

 vesicles are connected by a small thread-like film, which 

 penetrates the epidermis of the leaf, and often goes com- 

 pletely through the leaf; but sometimes it only destroys 

 the epidermis of one side. The mildew, under favorable 

 circumstances, will appear upon different portions of the 

 leaf at the same time, and when this occurs the whole sur- 

 face is soon overrun the leaf soon changes its color and 

 its functions are destroyed. 



The fungus does not confine itself wholly to the leaf, but 

 often attacks the young green portions of the stem, and 

 lastly the fruit. There are doubtless several species of 

 fungi that feed upon the grape, but the causes that favor 

 the growth of one will probably be congenial to others, and 

 for practical purposes they may all be considered as one. 

 The fruit of our indigenous varieties is not so liable to be 

 infested by mildew as the leaves, but when they are much 

 weakened by it the fruit will seldom entirely escape. The 

 fruit of the foreign varieties, when grown in this country in 

 the open air, will usually be more affected than the leaves, 

 and the same is true with the Southern varieties when grown 

 at the North. 



Young vines are more liable to mildew than older ones, 

 and those grown under glass are often very much injured 

 by it. A confined humid atmosphere is very productive 

 of mildew ; and though its ravages may often be checked 

 by a liberal application of sulphur and proper ventilation, 

 still, plants that have once become weakened by it are more 



