CHAP. CV. CORYLA^CE^. QUe'rCUS. 1823 



insects, chiefly belonging to the order Herafptera of Linnfeus (Homoptera 

 Lati:), and furnished with an elongated rostrum, which they introduce with- 

 out difficulty into the soft substance of the young parts, and thereby imbibe a 

 sufficient supply of nourishment. Amongst these are to be mentioned, Psylla 

 quercus, Eriosoma quercus, A'phis quercus, and A^phis roboris. Coccus 

 ' quercus Linn, is a species about the size of a pea, which attaches itself 

 to the branches at the base of the young stems. Another insect of the 

 same genus, of a species not j'et determined, is more injurious, as we learn 

 from a communication made by M. Victor Audouin to the Entomological 

 Society of France, on the 6th of April last (1836), by whom a portion of the 

 bark of an oak, of about thirty years' growth, was exhibited, entirely covered 

 with specimens of a coccus about the size of a pin's head. These insects were 

 of a greenish or orange }'ellow colour, and were females, destitute of motion, 

 adhering to the tree by means of their rostrum, which had pierced the bark. 

 The oak had been in a languishing state, and was condemned to be cut down 

 by the director of the Bois de Bologne, having, as M. V. Audouin judges, 

 been brought into this state by the presence of many millions of these insects, 

 which covered the entire trunk from 6 in. above the ground to the top, 

 completely altering the natural colour of the tree, as from 50 to 100 might be 

 counted in the space of a square inch. 



Tke Acorns are devoured by the larvte of a small weevil belonging the genus 

 Balaninus (B. glandium), and very nearly related to the nut weevil ; as well 

 as by the larva of Tinea Pomonella (according to Geoffroy). 



Galls. The various parts of the oak are also subject to the attacks of dif- 

 ferent species of hymenopterous insects belonging to the Linna^an genus Cy- 

 nips (fam. Cynipidae Westw.), Diplolepis OUv. and Leach, or gall flies, so named 

 from the various excrescences which they produce upon theleaves, stems, &c.; 

 and which are designed by nature to protect the delicate ova and larva? of 

 certain insects. Entomologists say that the tuniours on the leaf stalks, and 

 those on the fruit stalks, are produced by different species of Cynipidae ; that 

 the galls on the branch are produced by a distinct lly from that which pro- 

 duces the gall on the leaf; and it has also been ascertained, that the gall flies 

 on the oak leaf are of at least three different kinds. There are also distinct 

 kinds of gall flies for the root, bark, bud, and acorn cup, independently of the 

 kermes and gall nut. The various species have been named, C. quercus folii 

 Linn., C. q. baccarum Linn., C. q. inferus Linn., C. q. petioli Linn., C. q. 

 ramuli Linn., C, q. curticis Linn., C. q. gemmae Linn., C. q. pedunculi Linn., 

 C. q. calycis, C. q. terminiilis Fab., &c. (See also M. d'Anthoine's Cynipedo- 

 logie du Chene rouge in the Nouv. Journ. de Physique, t. i. p. 34 — 39.) 



There is another circumstance, also, connected with this subject, of con- 

 siderable interest in a physiological point of view (independently of the man- 

 ner in which the gall, consequent upon the puncture of an insect is formed), 

 and which is thus alluded to by Dr. Johnston of Berwick : — " We observe that 

 the irritation caused by the deposition and evolution of the egg will produce 

 growth of the most curious kind ; and differences in the irritation, too slight 

 to be traced, will occasion very remarkable difl'erences in the appearance of 

 the growth. Thus, in the oak leaf, one insect irritation produces a globular 

 smooth ball ; and another, a depressed tumour, covered with a hairy scarlet 

 coat. The first is seated on the substance of the leaf, and cannot be removed 

 without destroying the texture of the part; the other seems almost placed on 

 the leaf, and can be detached with facility. Examples equally remarkable 

 will occur to every one who has paid any attention to this curious subject; 

 and the growths appear to be not less uniform, and not less organised, than 

 many parasitical fungi." (^Flora of Berwick upon Tweed, vol. ii. p. 108.) 



The British oak does not bear a gall nut of such powerful qualities as that 

 of Q. infectoria ; but, like the galls of commerce, those British galls are said to 

 be the best from which the insect has not escaped. The largest species of 

 British galls is generally called the oak apple, or oak sponge (i'pongia guercina 

 of the ancients). These are produced by C. q. terminalis Fab. {Rcauni, 



G c 



