133 



to be attacked by the disease, which passes then throug-h the same 

 series of stag-es described. If the under side of a diseased leaf be 

 examined with a hand-lens, a minute round hole may be seen in 

 the center of each discolored spot, and this leads into a chamber 

 within the thickness of the leaf, in which live the mites that pro- 

 duce the disease. 



The discolorations and appearances of injury above described 

 are due entirely to the work of a microscopic mite, about one six- 

 hundredth of an inch in leng-th, belong-ing- to the ^Q.n\x% En'ophycSy 



peculiar in its long- and almost 

 worm-like body and in the posses- 

 sion of onl^' two pairs of legs, 

 placed close together near the 

 front end. These minute crea- 

 tures, which pass the winter be- 

 tween the bud scales, move to the 

 3'oung- leaves even before these 

 unfold, g-o throug-h the epidermis 

 on the under side, and feed upon 

 the cellular tissue of the interior 

 of the leaf. The destruction of 

 substance and disturbance o f 

 g-rowth thus caused, g^ive rise to 

 a thickening- of the leaf, forming- 

 what is commonly called a g-all, 

 and finally cause the death of the 

 injured tissue. As the leaves 

 ripen and dry the mites escape 

 throug-h the opening's of the galls 

 and take refug-ein the buds, where 

 as many as fifteen or twenty may 

 often be found under a sing-le 

 scale. 



It is often dif&cult to find a per- 

 fectly clean leaf on a badly in- 

 fested tree, and often more than 

 half the leaf substance may be 

 killed by midsummer. Badly injured trees shed their leaves sooner 

 than others, and " without its leaves the tree cannot store up the 

 necessary food in its winter buds to insure a healthy vig-orous tree 

 and a full crop the next season." — (Slingerland.) 



The progress of the disease can be arrested only by the destruc- 

 tion of the mites. This may be accomplished where there are but 



Fig. 19. 



The Peak-leaf Blister ; 

 later stage (sjiots dark 

 brown). 



