ANACH'ARIS, a genus of plants of the natural order hydrocharidece (q.v.), of which a species, A. aleinastruin (elodea canadensts of some botanists), has recently become natu ralized in Britain, suddenly appearing in so great abundance as to impede the navigation of some rivers and canals. It is a native of North America, growing in ponds and slow streams and is a dark-green, much-branched perennial, entirely floating under water, its flowers only appearing abode water for a very short time at the period of fer tilization, as in others of the order to which it belongs. It has numerous leaves, which are either opposite, or in whorls of 3 or 4, without foot-stalks, linear-oblong, transpa rent, 3 to 4 lines long. The female flowers are sessile in the upper axils, and are inclosed in a small 2-lobed spathe; the slender tube of the perianth is often 2 or 3 in. long, so as to attain the surface of the water, where it terminates in three or six small spreading seg ments. The male flowers are seldom observed. The plant was first found in Britain in 1842, by the late Dr. Johnston of Berwick, in the lake of Dunse castle; and again in 1847 by Miss Kirby, in the reservoirs of a canal in Leicestershire. It is now very abundant and troublesome in the Trent, Derwent, and other rivers. Its rapidity of growth is extraordinary. Immense masses disfigure the shallows of the Trent, and cover the beds
of the deeps. It strikes its shoots under the mud in a lateral direction for 6 in. or 1 ft., and then rises and spreads. The stems are very brittle, and every fragment is capable of growing, so that the means usually adopted to get quit of it serve rather for its propagation. It appears, however, that water-fowl are very fond of it; and by them, probably, its seeds may be conveyed from one river to another. It has been found that swans may be fed upon it with advantage, and its excessive growth kept down moue effectually in this way than in any other. It is supposed to be a great impediment to the progress of salmon ascending the rivers in which it occurs; but for some kinds of fish it probably affords both food and shelter. The manner of its introduction into Britain is unknown, although it has been conjectured that it may have escaped from some gar den-pond—a conjecture the more doubtful, from the distance between the localities in which it was first found; but its rapid increase is,of great -scientific interest, in connect Von with the important subject of the distribution of species. As being calculated to block up water-courses, the plant involves some serious economic considerations.