AQUATIC PLANTS, plants growing in or belonging to water. The presence of water is not only essential to the ac tive life of all organisms, but is pecul iarly necessary for plants which are for the most part dependent for food supply on matter dissolved in water, as well as on the carbonic anhydride mingled with the surrounding medium. Numerous plants are, moreover, in the strict sense ofthe word aquatic, having never ac quired or having lost all direct connec tion with the soil. The simplest plants or alga are almost all aquatic, though many occur in damp situations on land, or on other organisms, while others re main for long periods quiescent in com parative dryness. Many alga are abso lutely isolated in the water, while others are more or less intimately fixed to some solid substratum. Some rhizocarps, such as salvinia, are aquatic, with leaves rising to the surface, while others are land or marsh plants, like the higher horse-tails and club-mosses.
Among the flowering plants, or phan erogams, a return to aquatic life is ex hibited by numerous, though exceptional cases, while a very large number grow in moist situations, and have a semi aquatic habit. The simple monocotyle
dons, known as helobiew, or marsh lilies, are more or less strictly water-plants. The arrowhead (sagittaria), and other alismacem; the butomis of the marshes; hydrocharis, with floating kidney-shaped leaves; the water soldier (stratiotes), with narrow submerged leaves; and the Canadian pond weed (anacharis). Among dicotyledons, the white water buttercup (ranunculus aquati/is), with its slightly divided floating, and much dissected submerged leaves; the yellow and white water-lilies (nymphwa); the sacred lotus flower of the Ganges and Nile (nelumbium); the gigantic Victoria regia of tropical South America; and the insectivorous bladderwort or utricularia, are among the most familiar aquatic forms.