124 THE HAWTHORN. 



one thing, one may study there the various ways in which insect 

 habit affects the appearance of bushes and even of timber trees. A 

 silvery web coverinu; bird-cherry or troat-willow is the shelter of 

 countless grubs ; the beautiful crimson bedeguar of the rose-bush is 

 the handicraft of gall-flies. These insects especially affect the oak 

 tree ; they cover and almost conceal its catkins with currant-like 

 galls, set their studs upon its leaves, and produce "oak-apples," round 

 woody galls and artichoke galls, upon its branches, in sufficient 

 numbers to alter the appearance of the tree. The pine-galls, so closely 

 resembling young cones, are hardly less conspicuous, and the leaves of 

 the Willow and the leaf-stalks of the Black Poplar fall victims to the 

 same pest. The young shoots of the Limes are sometimes forced into 

 a cur\'e by the punctures of a species of aphis. More noticeable 

 than any of the foregoing are the knotted woody masses which form 

 round the twigs of willows; they resemble the " birdsnest " excres- 

 cences which disfigure the Hornbeam, Birch and Thorn, though these 

 last are probably due rather to excess of nourishment in the soil 

 than to the puncture of the young shoots, as in the first-named tree. 

 The shoots of the Hawthorn are sometimes attacked by a grub, and 

 a kind of leaf-gall is produced, in the form of a mass of small 

 prickly leaves surrounding a ball of withered ones in which the 

 insect conceals itself 



An abnormal form or positic>n in a leaf often indicates that a 

 caterpillar has taken possession ; some may be rolled up from tip t 

 base, others from side to side, or the two layers of the leaf-blade 

 may be split, and a tunnel forced between the two fragile walls. 

 The gum exuding from insects alters the texture of the leaf, while 

 lichens, vegetable parasites of varied form and colouring, are often 

 more conspicuous than the bark to which they cling. 



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