In pools we sometimes meet with floating plants that have no true roots, at least at the time of flowering, but consist of a tuft of long, rootlike, submerged branches, bearing much-divided leaves, and sending leafless stalks of yellow flowers above the surface of the water. These plants are the Bladderworts (_Utricularia_), of the order _Lentibulaceæ_, and are so called because they have little air-bladders either attached to the leaves or supported on leafless branches. The leaves are divided into numerous very narrow segments, thus presenting a proportionately large amount of surface to the water for the absorption of dissolved gases required by the plant; and the flowers consist of a deeply two-lobed calyx; a spurred corolla, with its mouth closed or nearly closed by means of a convex 'palate'; two stamens; and a one-celled ovary that ripens into a globular fruit. [Illustration: THE GREATER BLADDER-WORT.] As to the little air-bladders mentioned above, they form, perhaps, the most interesting feature of the plant, for they are the traps by means of which small aquatic creatures are caught, and also the organs concerned in the absorption of nutritive products derived from the prey. Each bladder has an opening, guarded by a kind of valve which allows easy ingress, but no exit. It does not seem to produce any secretion which would hasten the death of the creatures entrapped, nor does it appear to produce any kind of digestive fluid, as is the case with other carnivorous plants; but small aquatic creatures, such as water-fleas, cyclops, very small larvæ, &c., entering the bladders for shelter or some other purpose, are securely imprisoned until they die of starvation or suffocation; and their bodies then decay, giving rise to soluble gases and other products which are absorbed into the plant by special cells within the bladder. There are three British species of these plants--the Greater, the Lesser, and the Intermediate Bladder-worts. The first of these--_Utricularia vulgaris_--is rather local in its distribution, and is easily distinguished from the other two by its superior size, having floating branches from a few inches to a foot in length. The second (_U. minor_) is much more common. Its floating branches are only two or three inches long at the time of flowering, but they grow longer after; and the flowers are pale yellow, with a short, broad spur. The third (_U. intermedia_), which is very local, has also pale yellow flowers, but with a much longer spur; and the bladders are at the ends of leafless branches.