The Canadian Horticulturist. 



243 



spider 



THE PEAR LEAF BLISTER. 



E have several times received from subscribers in various parts of 

 our province, samples of pear leaves having black corkey spots upon 

 them, and these were either a mystery to the senders, or else sup- 

 posed to be either leaf blight, or scab. After consultation with Prof. 

 Fletcher, of the Central Experimental Farm, we were able to reply 

 that the cause of the trouble was a minute mite, Phytoptus pyri 

 belonging to the same order (Acarina) as the cattle tick, and the itch 

 671 shows an adult mite, greatly magnified. Indeed, these mites 



are so small that they cannot be seen 

 without a glass, and to study their 

 structures a first class microscope is 

 necessary. 



Bulletin 61 of the Cornell Experi- 

 mental Station, gives a most excel- 

 lent account of this mite, written by 

 Fig. 671. Prof. Slingerland. To give an idea 



of their diminutive size, he says that it would take 150 of them placed end to 

 end, and 600 side by side to measure an inch. These tiny mites winter under- 

 neath the outer scales of the buds, fifteen or twenty having been found under- 

 neath a single bud scale. Thus situated, they are ready for mischief early in 

 spring. 



The diseased portions of the leaves are really galls, produced by these 

 mites, and within them the eggs are depos- ^ 



ited ; they are quite easily distinguished 

 from the fungus spots, by their blister- 

 like corkey appearance. Fig. 672, from 

 the bulletin referred to, shows a highly 

 magnified section of a pear leaf through 

 one of these galls, g, showing gall ; «, //> 

 normal structure of leaf; <?, opening of the 

 gall ; and e, eggs of the mite. 



Later in the season the galls dry and turn brown or black, and are more 

 conspicuous on the lower side The leaf in the mean time has shrunk to its 

 normal thickness, as shown in Fig. 673, in which g is gall, fi n, uninjured por- 

 tion of leaf, and o, opening to gall from under side. 



Fk;. 672.— Gall Bllster Mite ; Red 

 Stage. 



Fio. 673 —Gall of Blister Mite, Dry Staoe. 



