88 phytoptid;e. 



they are most noticed. They may l)e red or green, or red on one side 

 of the leaf and green on the other, and later on, presmnably from 

 death of the diseased tissues, the blisters turn blackish or brown in 

 colour. 



Though it is only within the last few years that anything to call 

 enquiry worth speakmg of has been sent me about these leaf-blisters, 

 I have myself had them more or less under observation since about 

 the year 1876, and have found that confusion is apt to arise between 

 these blisters and the small discoloared patches of mere vegetable 

 disease often found on Pear-leaves, and sometimes known as Pear 

 Scab ; but a little examination with a hand-magnifier, so as to distin- 

 guish the swelling of the blister on both sides of the leaf, and the 

 central hole below, and if a section is cut, the disorganized tissue 

 with something of a cavity between the two sides of the blister, with 

 very possibly the long cylindrical Gall Mites within, will show the 

 difference. 



The above are well-marked points, and, as will be seen by some of 

 the following communications sent me in the past season, catch the 

 eye at once. 



On the 30th of April, Mr. W. H. Burbidge, writing from Marlyns, 

 Guildford, forwarded me specimens of bad attack of Pear Leaf-blister 

 Mite, with the observation : — " Enclosed I send you a few leaves from 

 a Pear that appears to be attacked by some insect. I see a small hole 

 in the centre of the swellings (under side of the leaf) with the micro- 

 scope, but I cannot discover any insect in the blister-like places. 



" Last week, in Somersetshire, I saw two Pear trees similarly 

 attacked ; there the very young leaves that had not even uncurled 

 seemed affected." — (W. H. B.) 



A few days later, Mr. Sidney Lee, writing from Crocken Hill, 

 Swanley, Kent, forwarded me some Pear-leaves suffering from the 

 "blister," with the observation that he had a number of trees with 

 leaves in a similar condition. The specimens sent were like most of 

 the others forwarded at that time, with the blister-diseased parts of a 

 reddish or reddish purple colour ; and, in the U. S. A. Report above 

 referred to, it is noted (on the first page) that " the disease appears on 

 the Pear-leaves before they are fully expanded from the bud in the 

 spring in the form of red blister-like spots, an eighth of an inch or 

 more in diameter." — (M. V. S.) 



Some other observations were sent giving the opportunity of 

 experiment as to remedial treatment noticed at p. 91 under this head. 



With regard to the Phytoptus pyri, the Leaf-blister Mite, or Gall Mite, 

 which causes this attack, it is almost or quite invisible to the naked 

 eye, being very much less than one millimetre in length,* and its 



* One millimetre is the 25th part of an inch. 



