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 of the tissues, rather than the specific peculiarities or the part of the plant affected, that principally determines the nature of the gall. Thus the characteristics of the currant-gall of Spathegaster baccarum, L., which occurs alike on the leaves and on the flower-stalks of the oak, are obviously due to the act of oviposition, and not to the functions of the parts producing it; the bright red galls of the saw-fly Nematus gallicola are found on four different species of willow, Salix fragilis, S. alba, S. caprea and S. cinerea; and the galls of a Cynipid, Biorhiza aptera, usually developed on the rootlets of the oak, have been procured also from the deodar. Often the gall bears no visible resemblance to the structures out of which it is developed; commonly, however, outside the larval chamber, or gall proper, and giving to the gall its distinctive form, are to be detected certain more or less modified special organs of the plant. The gall of Cecidomyia strobilina, formed from willow-buds, is mainly a rosette of leaves the stalks of which have had their growth arrested. The small, smooth, seed-shaped gall of the American Cynips seminator, Harris, according to W. F. Bassett, is the petiole, and its terminal tuft of woolly hairs the enormously developed pubescence of the young oak-leaf. The moss-like covering of the “bedeguars” of the wild rose, the galls of a Cynipid, Rhodites rosae, represents leaves which have been developed with scarcely any parenchyma between their fibro-vascular bundles; and the “artichoke-galls” or “oak-strobile,” produced by Aphilothrix gemmae, L., which insect arrests the development of the acorn, consists of a cupule to which more or less modified leaf-scales are attached, with a peduncular, oviform, inner gall. E. Newman held the view that many oak-galls are pseudobalani or false acorns: “to produce an acorn has been the intention of the oak, but the gall-fly has frustrated the attempt.” Their formation from buds which normally would have yielded leaves and shoots is explained by Parfitt as the outcome of an effort at fructification induced by oviposition, such as has been found to result in several plants from injury by insect-agency or otherwise. Galls vary remarkably in size and shape according to the species of their makers. The polythalamous gall of Aphilothrix radicis, found on the roots of old oak-trees, may attain the size of a man’s fist; the galls of another Cynipid, Andricus occultus, Tschek, which occurs on the male flowers of Quercus sessiliflora, is 2 millimetres, or barely a line, in length. Many galls are brightly coloured, as, for instance, the oak-leaf hairy galls of Spathegaster tricolor, which are of a crimson hue, more or less diffused according to exposure to light. The variety of forms of galls is very great. Some are like urns or cups, others lenticular. The “knoppern” galls of Cynips polycera, Gir., are cones having the broad, slightly convex upper surface surrounded with a toothed ridge. Of the Ceylonese galls, “some are as symmetrical as a composite flower when in bud, others smooth and spherical like a berry; some protected by long spines, others clothed with yellow wool formed of long cellular hairs, others with regularly tufted hairs.” The characters of galls are constant, and as a rule exceedingly diagnostic, even when, as in the case of ten different gall-gnats of an American willow, Salix humilis, it is difficult or impossible to tell the full-grown insects that produce them from one another. In degree of complexity of internal structure galls differ considerably. Some are monothalamous, and contain but one larva of the gall-maker, whilst others are many-celled and numerously inhabited. The largest class are the unilocular, or simple, external galls, divided by Lacaze-Duthiers into those with and those without a superficial protective layer or rind, and composed of hard, or spongy, or cellular tissue. In a common gall-nut that authority distinguished seven constituent portions: an epidermis; a subdermic cellular tissue; a spongy and a hard layer, composing the parenchyma proper; vessels which, without forming a complete investment, underlie the parenchyma; a hard protective layer; and lastly, within that, an alimentary central mass inhabited by the growing larva.

Galls are formed by insects of several orders. Among the Hymenoptera are the gall-wasps (Cynips and its allies), which infect the various species of oak. They are small insects, having straight antennae, and a compressed, usually very short abdomen with the second or second and third segments greatly developed, and the rest imbricated, and concealing the partially coiled ovipositor. The transformations from the larval state are completed within the gall, out of which the imago, or perfect insect, tunnels its way,—usually in autumn, though sometimes, as has been observed of some individuals of Cynips Kollari, after hibernation.

Among the commoner of the galls of the Cynipidae are the “oak-apple” or “oak-sponge” of Andricus terminalis, Fab.; the “currant” or “berry galls” of Spathegaster baccarum, L., above mentioned; and the “oak-spangles” of Neuroterus lenticularis, Oliv., generally reputed to be fungoid growths, until the discovery of their true nature by Frederick Smith, and the succulent “cherry-galls” of Dryophanta scutellaris, Oliv. The “marble” or “Devonshire woody galls” of oak-buds, which often destroy the leading shoots of young trees, are produced by Cynips Kollari, already alluded to. They were first introduced into Devonshire about the year 1847, had become common near Birmingham by 1866, and two or three years later were observed in several parts of Scotland. They contain about 17% of tannin. On account of their regular form they have been used, threaded on wire, for making ornamental baskets. The large purplish Mecca or Bussorah galls, produced on a species of oak by Cynips insana, Westw., have been regarded by many writers as the Dead Sea fruit, mad-apples (mala insana), or apples of Sodom (poma sodomitica), alluded to by Josephus and others, which, however, are stated by E. Robinson (Bibl. Researches in Palestine, vol. i. pp. 522-524, 3rd ed., 1867) to be the singular fruit called by the Arabs ’Ösher, produced by the Asclepias gigantea or procera of botanists. What in California are known as “flea seeds” are oak-galls made by a species of Cynips; in August they become detached from the leaves that bear them, and are caused to jump by the spasmodic movements of the grub within the thin-walled gall-cavity.

Common gall-nuts, nut-galls, or oak-galls, the Aleppo, Turkey, or Levant galls of commerce (Ger. Galläpfel, levantische Gallen; Fr. noix de Galle), are produced on Quercus infectoria, a variety of Q. Lusitanica, Webb, by Cynips (Diplolepis, Latr.) tinctoria, L., or C. gallae tinctoriae Oliv. Aleppo galls (gallae halepenses) are brittle, hard, spherical bodies, - in. in diameter, ridged and warty on the upper half, and light brown to dark greyish-yellow within. What are termed “blue,” “black,” or “green” galls contain the insect; the inferior “white” galls, which are lighter coloured, and not so compact, heavy or astringent, are gathered after its escape (see fig. 1.). Less valued are the galls of Tripoli (Taraplus or Tarabulus, whence the name “Tarablous galls”). The most esteemed Syrian galls, according to Pereira, are those of Mosul on the Tigris. Other varieties of nut-galls, besides the above-mentioned, are employed in Europe for various purposes. Commercial gall-nuts have yielded on analysis from 26 (H. Davy) to 77 (Buchner) % of tannin (see