176 On the Diseases of Fruit Trees. 



deposited under favourable circumstances, speedily vegetate, 

 and in their turn rapidly extend themselves. The species of 

 Mildew which attacks the Peach, appears to confineitself to 

 that class of trees alone, and differs obviously from those spe- 

 cies which may be observed to grow on the leaves of the Apple, 

 Pear, Hawthorn, or such other plants as have come under my 

 observation, in its greater size and luxuriance. To the naked 

 eye in the earlier stages of its growth, the Mildew seems a 

 hairy down, which, seen through an ordinary magnifying 

 glass, is erect and crystalline ; at a later period, its stems 

 appear flattened like a web to the leaf, to the exterior part 

 oF which it attaches itself, before it is unfolded, and princi- 

 pally confines itself afterwards to that part, it being more 

 tender and spongy, than the inner or upper side, and afford- 

 ing a fitter nidus in which the germinating seed may establish 

 itself. The leaf so attacked, never expands perfectly, by 

 which means an experienced eye may readily distinguish the 

 disease on its first approaches ; from the leaves the Mildew 

 extends to the tender extremities of the young shoots, and 

 fruit, and finally destroys the tree, unless arrested in its pro- 

 gress by timely attention. Of the two classes of Peach trees, 

 those which have glands and those which are devoid of 

 them, the former is but slightly, if at all, affected by the 

 disease in these climates, in consequence, probably, of their 

 possessing a closer and firmer cuticle, which is impervious to 

 the seed of the mildew ; and of the latter, some sorts are 

 liable to it in a much greater degree than others, parti- 

 cularly the Red Magdalen, one of our very best kinds of 

 Peaches. 



That the disease is contagious I have always had reason to 



