128 PEAR. 



of the leaf and green on the other ; and later on, presumably 

 from death of the diseased tissues, the blisters turn blackish 

 or brown in colour. 



Some confusion is apt to arise between these blisters and 

 the small discoloured 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 dis- 

 tinguish the swelling of the blister on both sides of the leaf, 

 and the central hole below, and if a section is cut, the dis- 

 organized tissue with something of a cavity between the two 

 sides of the blister, with very possibly the cylindrical gall- 

 mites within, will show the difference. 



Witli regard to the Phytoptus miri, 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 breadth only about one-fifth or 

 sixth part of its length. The greatly magnified figure at 

 p. 126, copied by kind permission of Dr. Nalepa from one of 

 his excellent figures, shows the shape perfectly. It is cylin- 

 drical, tapering at the tail, with a strong slightly curved 

 proboscis, and four legs, which are distinctly jointed ; the 

 terminal claw, variously known as a "holding-claw" or 

 "feather bristle," is four-branched. The abdomen is uni- 

 formly ringed, and rather finely punctate. Without very 

 strong microscopic power, far beyond what most of us possess, 

 it is impossible to identify one from the other the different 

 species of Phytoptus ; but with this Pear Leaf-blister the 

 attack may for all practical purposes be identified by the 

 existence of the blister ; and with moderately strong magni- 

 fiers the mites may be distinguished as gall-mites, or as of 

 the subfamily of Phytoptida, from others of the order Acarina 

 — to which they belong— by their narrow cylindrical shape, 

 and by having throughout their lives only two pairs of legs. 

 They are hatched from the egg with two pairs, placed as 

 shown in the figure at the fore part of the body, and they 

 never have more. This is a most important point to be 

 attended to, as, for want of knowledge of this fact, observa- 

 tions are at times hopelessly confused as to what kind of 

 infestation is present, and consequently what treatment 

 needed. 



This Pear-leaf infestation is not often enquired about, but 

 personally I have had it more or less under observation since 

 the year 1876, and whenever I needed specimens have been 

 able to find them on the Pear leafage in the garden I occupied 

 for some time near London, and later on here at St. Albans. 



In the year 1893, in which mite-galls caused by Phytopti 



* As previously mentioned, one millimetre is the 25th part of an inch. 



