Page:EB1911 - Volume 11.djvu/442

Rh Vinen, ''loc. cit.''), with gallic and ellagic acids, ligneous fibre, water, and minute quantities of proteids, chlorophyll, resin, free sugar and, in the cells around the inner shelly chamber, calcium oxalate. Oak-galls are mentioned by Theophrastus, Dioscorides (i. 146), and other ancient writers, including Pliny (''Nat. Hist.'' xvi. 9, 10, xxiv. 5), according to whom they may be produced “in a single night.” Their insect origin appears to have been entirely unsuspected until within comparatively recent times, though Pliny, indeed, makes the observation that a kind of gnat is produced in certain excrescences on oak leaves. Bacon describes oak-apples as “an exudation of plants joined with putrefaction.” Pomet thought that gall-nuts were the fruit of the oak, and a similar opinion obtains among the modern Chinese, who apply to them the term Mu-shih-tsze, or “fruits for the foodless.” Hippocrates administered gall-nuts for their astringent properties, and Pliny (''Nat. Hist.'' xxiv. 5) recommends them as a remedy in affections of the gums and uvula, ulcerations of the mouth and some dozen more complaints. In British pharmacy gall-nuts are used in the preparation of the two astringent ointments unguentum gallae and unguentum gallae cum opio, and of the tinctura gallae, and also as a source of tannin and of (q.v.). They have from very early times been resorted to as a means of staining the hair of a dark colour, and they are the base of the tattooing dye of the Somali women. The gall-making Hymenoptera include, besides the Cynipidae proper, certain species of the genus Eurytoma (Isosoma, Walsh) and family Chalcididae, e.g. E. hordei, the “joint-worm” of the United States, which produces galls on the stalks of wheat; also various members of the family Tenthredinidae, or saw-flies. The larvae of the latter usually vacate their galls, to spin their cocoons in the earth, or, as in the case of Athalia abdominalis, Klg., of the clematis, may emerge from their shelter to feed for some days on the leaves of the gall-bearing plant.

The dipterous gall-formers include the gall-midges, or gall-gnats (Cecidomyidae), minute slender-bodied insects, with bodies usually covered with long hairs, and the wings folded over the back. Some of them build cocoons within their galls, others descend to the ground or become pupae. The true willow-galls are the work either of these or of saw-flies. Their galls are to be met with on a great variety of plants of widely distinct genera, e.g. the ash, maple, horn-beam, oak, grape-vine, alder, gooseberry, blackberry, pine, juniper, thistle, fennel, meadowsweet, common cabbage and cereals. In the northern United States, in May, “legions of these delicate minute flies fill the air at twilight, hovering over wheat-fields and shrubbery. A strong north-west wind, at such times, is of incalculable value to the farmer.” Other gall-making dipterous flies are members of the family Trypetidae, which disfigure the seed-heads of plants, and of the family Mycetophilidae, such as the species Sciara tilicola, Löw, the cause of the oblong or rounded green and red galls of the young shoots and leaves of the lime.

Galls are formed also by hemipterous and homopterous insects of the families Tingidae, Psyllidae, Coccidae and Aphidae. Coccus pinicorticis causes the growth of patches of white flocculent and downy matter on the smooth bark of young trees of the white pine in America. The galls of examples of the last family are common objects on lime-leaves, and on the petioles of the poplar. An American Aphid of the genus Pemphigus produces black, ragged, leathery and cut-shaped excrescences on the young branches of the hickory.

The Chinese galls of commerce (Woo-pei-tsze) are stated to be produced by Aphis Chinensis, Bell, on Rhus semialata, Murr. (R. Bucki-amela, Roxb.), an Anacardiaceous tree indigenous to N. India, China and Japan. They are hollow, brittle, irregularly pyriform, tuberculated or branched vesicles, with thin walls, covered externally with a grey down, and internally with a white chalk-like matter, and insect-remains (see fig. 2). The escape of the insect takes place on the spontaneous bursting of the walls of the vesicle, probably when, after viviparous (thelytokous) reproduction for several generations, male winged insects are developed. The galls are gathered before the frosts set in, and are exposed to steam to kill the insects.

Chinese galls examined by Viedt yielded 72% of tannin, and less mucilage than Aleppo galls. Several other varieties of galls are produced by Aphides on species of Pistacia.

M. J. Lichtenstein has established the fact that from the egg of the Aphis of Pistachio galls, Anopleura lentisci, is hatched an apterous insect (the gall-founder), which gives birth to young Aphides (emigrants), and that these, having acquired wings, fly to the roots of certain grasses (Bromus sterilis and Hordeum vulgare), and by budding underground give rise to several generations of apterous insects, whence finally comes a winged brood (the pupifera). These last issuing from the ground fly to the Pistachio, and on it deposit their pupae. From the pupae, again, are developed sexual individuals, the females of which lay fecundated eggs productive of gall-founders, thus recommencing the biological cycle (see Compt. rend., Nov. 18, 1878, p. 782, quoted in Ann. and Mag. Nat. Hist., 1879, p. 174).

Of other insects which have been recognized as gall-makers there are, among the Coleoptera, certain Curculionids (gall-weevils), and species of the exotic Sagridae and Lamiadae and an