CHAP. CV.

coryla'ce.®. «ue'rcus.

1823

insects, chiefly belonging to the order Hemfptera of Linnaeus (HomopteraLatr.), and furnished with an elongated rostrum, which they introduce with-out difficulty into the soft substance of the young parts, and thereby imbibe asufficient supply of nourishment. Amongst these are to be mentioned, Tsyllaquercus, Eriosoina quercus, A'phis quercus, and A'phis rdboris. Coccusquercus Linn, is a species about the size of a pea, which attaches itselfto the branches at the base of the young stems. Another insect of thesame genus, of a species not yet determined, is more injurious, as we learnfrom a communication made by M. Victor Audouin to the EntomologicalSociety of France, on the 6th of April last (1836), by whom a portion of thebark of an oak, of about thirty years’ growth, was exhibited, entirely coveredwith specimens of a coccus about the size of a pin’s head. These insects wereof a greenish or orange yellow 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 downby 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 becounted in the space of a square inch.

The Acorns are devoured by the lame of a small weevil belonging the genusBalaninus (B. glandium), and very nearly related to the nut weevil; as wellas 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 Linmean genus Cy-nips (fam. Cynipid® Westiu.), Dipldlepis O/iv. and Leach, or gall flies, so namedfrom the various excrescences which they produce upon the leaves, stems, &c.;and which are designed by nature to protect the delicate ova and larvae ofcertain insects. Entomologists say that the tumours on the leaf stalks, andthose on the fruit stalks, are produced by different species of Cynipid®; thatthe galls on the branch are produced by a distinct fly from that which pro-duces the gall on the leaf; and it has also been ascertained, that the gall flieson the oak leaf are of at least three different kinds. There are also distinctkinds of gall flies for the root, bark, bud, and acorn cup, independently of thekermes and gall nut. The various species have been named, C. quercus fhliiLinn., C. q. baccarum Linn., C. q. inferus Linn., C. q. petioli Linn., C. q.ramuli Linn., C. q. corticis Linn., 0. q. gemm® Linn., C. q. pedunculi Linn.,C. q. calycis, C. q. terminalis 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 thatthe irritation caused by the deposition and evolution of the egg will producegrowth of the most curious kind; and differences in the irritation, too slightto be traced, will occasion very remarkable differences in the appearance ofthe growth. Thus, in the oak leaf, one insect irritation produces a globularsmooth ball; and another, a depressed tumour, covered with a hairy scarletcoat. The first is seated on the substance of the leaf, and cannot be removedwithout destroying the texture of the part; the other seems almost placed onthe leaf, and can be detached with facility. Examples equally remarkablewill 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, thanmany 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 thatof Q. infectoria; but, like the galls of commerce, those British galls are said tobe the best from which the insect has not escaped. The largest species ofBritish galls is generally called the oak apple, or oak sponge (Spongia quercinaof the ancients). These are produced by C. q- terminalis Fab. (lleaum.

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