226 BOARD OF AGRICULTURE. 



make a special study of fungi. Many tumors are known to 

 be caused by insects ; and, as a rule, the distortion produced 

 arises, not so much from the attack of the insects themselves 

 as from the effort of the plant-cells in succeeding years to 

 perform their normal work. The injury often consists in the 

 invasion of a leaf-bud by some very small insect ; and, as a 

 result of the irritation, the leaves constituting the bud en- 

 large, become hardened, and often unite into a comparatively 

 solid mass. The next year the indurated mass itself acts as a 

 foreign body ; and there grows around it in succeeding years 

 layers, which are all more or less distorted, until finally we 

 have a large knot in which it is quite impossible to detect 

 the original lesion. 



In the beginning of the lecture we divided diseases caused 

 by fungi into two general classes, — tumors and blights. 

 The latter is by far the larger and most destructive, and 

 more generally recognized as caused by fungi. Of course, 

 the consideration of blights on fruit-bearing plants should 

 not be kept distinct from that of blights on vegetables ; for, 

 in a scientific point of view, the}'" are very closely related. 

 To describe in detail even a small portion of the blights 

 of cultivated plants would require several lectures ; and to- 

 day I can only call your attention to two which are common 

 on grape-vines in Massachusetts, and let them serve as 

 types of two large and very destructive orders of fungi. 

 The fungi to which I refer are found as well on wild grapes 

 as on cultivated ; and neither species is as yet known to 

 occur in Europe, although both are common throughout the 

 Eastern United States. 



You may have noticed that the leaves of many cultivated 

 grapes are apt to look dusty after the first of August. The 

 dustiness, if such it really were, would, of course, disappear 

 or diminish after a heavy rain. But such is not the case. 

 During the damp weather the dusty look increases; and, 

 after a while, the leaf dries and shrivels. As the leaf shriv- 

 els, the dustiness disappears ; and in its place we see a num- 

 ber of very small black bodies scattered all over both sur- 

 faces of the leaves. In some cases, instead of looking 

 dusty, the leaves seem to be covered with a tolerably thick 

 white web, which extends to the leaf-stalks, and in extreme 

 cases to the grapes themselves. The blight is often supposed 



