The phylloxera of the vine is a plant-louse or aphis, which exhibits an interesting adaptation of winged and wingless broods to the requirements of the insect’s nutrition and multiplication. A “foundress” hatches from an egg on the bark of the vine where it has passed the winter. It proceeds to attack the young leaves and to produce a brood of young. The leaves of the vine when thus attacked swell up and produce galls, in which the young phylloxera are enclosed, and there the phylloxeras continue to multiply, producing more galls and thus destroying the leaves. Some of the young broods now crawl down the vine to its roots; others stay on the leaves and continue their destructive work there. There are several varieties of form and size amongst these broods. Those which go to the roots attack the rootlets and produce knobs and swellings on them, leading to their destruction as feeding organs. Meanwhile the root-phylloxeras multiply exceedingly, and those on the leaves are still feeding and multiplying. From one foundress mother as many as twenty-five millions are produced in six months. At last in the autumn the root-parasites produce a winged generation of virgin-mothers, which come up from the ground and fly away to other vines, upon which they produce males and females. These females each lay a fertilised egg on the bark of the previously healthy vine, and so the infection is spread. The root-infesting forms continue to multiply, and in warm climates there is no cessation of this process even in winter. This parasite—the _Phylloxera vastatrix_—was introduced with some American species of grape-vine—brought over as experimental samples from Colorado—about 1864. In its native country it does comparatively little harm, for the roots of the American species of vine are, though attacked by it, not seriously injured. They have the property of throwing out new rootlets when those already existing are punctured and injured by the phylloxera, and so are not killed by the attack, as is the European grape-vine.