THE PEAE BLISTER-MTTE. 45 



The Avork of the mite on apple first shows on the upper surface of 

 the k^af as distinct light-cohered pimples, and on the underside as 

 blisters or thickened areas of the same color as the leaf. The affected 

 areas are of irreaudar size and are unevenly distributed, thoug'li the 

 larger proportion of them are about the sides and the base of the leaf. 

 Some of the blisters may have a reddish tinge, somewhat similar to 

 the pear leaf-galls, l)ut they are usually of a less brilliant color. As 

 the galls become older they appear as corky spots of a ^'eddish-brown 

 color, and not black, as with the pear, which to the touch are very dis- 

 tinct from the healthy })ortions of the leaf. The individiuil galls 

 average from one-twelfth to one-eighth of an inch in diameter and 

 are usually oval or quadrangular in shape. Leading to the interior 

 of each ati'ected area there is usually one or more tiny openings. 

 Often the spots coalesce, forming large irregular dead areas with 

 smooth or slightly raised surfaces and of a dark-brown color, which 

 rupture the leaves at the nuirgins. About July 1 the most striking 

 eti'ects of the mites upon the leaves appear, especially if there is much 

 yellowing of the foliage, as frequently occurs. Upon the upper sur- 

 face of such leaves the mite-infested spots are of a light-brown or of 

 a dark-green color and are uniformly broAvn beneath. These s])ots 

 are usually thickly nuissed, forming a dark, broad band of irregular 

 width along each side of the leaf, Avhicli contrasts conspicuously with 

 the intervening light-yellow area about the main rib. The mites also 

 cause pimples about the calyx cavity and on the stems of young 

 applets. In several instances the work of the mites upon the leaves 

 and fruit stems of the same cluster had so weakened the stems as to 

 cause the falling of the fruit. Prenuiture dropping of the apples by 

 this means seems to be of rare occasion, and even on the worst-infested 

 trees the loss of fruit is not appreciable. This seems incredible, as it 

 iloes not seem possible that the foliage of the trees could be so com- 

 pletely overrun with mites without losses in crop production. 



As has been stated by other observers, notably Prof. T. J. Burrill, 

 in his study of the species on pear, the mites spend the winter in the 

 buds, preferably under the second and third layers of the bud scales. 

 As the buds burst there is a movement of the mites to the unfolding 

 leaves, in which eggs are deposited. This migration takes place 

 with the maturing of the bud scales, during the latter part of April 

 and early iSIay, depending on the season, soon after which the discol- 

 oration of the leaves by pale and red-colored spots occurs. On pear 

 foliage the galls are largely grouped in a row on each side of the 

 nuiin rib, while on a]5ple leaves the affected areas appear in the great- 

 est numbers about the sides and the base of the leaf. This difference 

 in the arrangement of tlie diseased spots on apple and i)ear foliage 

 seems to be determined by the manner of the distribution of the pubes- 



