2 APPLE. 



same time is so open to remedy that it may with Httle 

 expense or trouble be prevented estabhshing itself. 



The presence of this " Apple-bark Plant-louse," or "Woolly 

 Aphis," may be easily detected by the woolly or cottony 

 growth on the insects, giving the appearance of a white film 

 growing at the bottom of the crevices where a few of them 

 are lurking. Where there are many the spot appears as if 

 a knot of cotton-wool was sticking to the bough, or even 

 hanging down in pieces several inches in length, ready to be 

 wafted by the first gust of wind, with all the insects in it, to 

 a neighbouring bough. 



The "BHght" is chiefly to be found in neglected Apple 

 orchards. Its headquarters are in crevices in the bark, or in 

 hollows where young bark is pressing forward over the surface 

 where a bough has been cut off, or broken by accident so as 

 to leave a shelter of the old dead bark outside ; it may, how- 

 ever, be found on almost every part of the tree into which the 

 aphis can pierce with its sucker ; and the harm caused by 

 the attack is not only from the quantity of sap drawn away 

 from the bark or j'oung shoots, but also from the diseased 

 growth which is thus set up. The bark is at first not much 

 affected by the punctures, but the woody layers beneath 

 become soft, pulpy, and swollen. The cells and fibres divide 

 and subdivide, and the bark splits open over the swelling, 

 showing the tissue beneath, which is thus exposed for a fresh 

 attack. 



At the end of summer these watery swollen growths dry up 

 and die, and thus form deep cracks. With the return of spring 

 (as in other cases of injury) a new growth forms round the 

 dead part, and this soft tissue is ready for the young aphides. 

 Thus, from the swollen diseased growth caused partly by the 

 aphides, partly by the natural attempts of the tree to repair 

 damage, a constantly increasing diseased mass arises, which 

 shelters the insects in its crannies, and finds food for them in 

 its young hypertrophied formations.* 



The "American Blight" Aphis is stated to have been im- 

 ported from America in 1787, but whether this is a fact 

 appears somewhat uncertain. It may be known at a glance 

 from the common Apple Aphis (scientifically Aphis mail), 

 which is injurious to the leaves, by the white wool with 

 which it is more or less covered, and from which it takes its 

 common name. 



The Woolly Apple Aphides are of the shape figured on 

 p. 1 and p. 3, magnified, with three pairs of legs, and (when 

 in winged condition) with two pairs of transparent wings ; a 



* See paper by M. Prillieux in ' Comptes Eendus ' for April, 1875. 



