Vallisneria, a genus of the natural order of plants Hydrocharideæ. Its one species, V. spiralis, is an aquatic found in fresh-water lakes and streams in the tropical and warm regions of the earth. They generally grow in running waters. V. spiralis is particularly celebrated on account of its peculiar process of fecunda- tion. At the time when this is to take place the flowers of the female plants rise to the surface of the water by means of their long spirally-twisted stalks. The flowers of the male plants, in order to follow them thither, become detached, having previously grown on short stalks at the bottom of the water, and expand, liberating their pollen, which, floating about upon the surface, comes in contact with the female flowers which are stationary. After fecundation the female flowers return under the water by the spiral contraction of their stalks, and the fruit is ripened under water. This plant is found in ditches and bogs in Italy and the south of France, and is frequently grown in aquaria in Britain and other countries. Considerable depth of water should be provided for it, as the leaves are long, and should always be submerged.