Utricularia (Lat. Utriculus A Little Bladder), the bladderwort, a genus of aquatic or marsh plants, of which there are more than 100 species, some of which are found in nearly all parts of the world, there being over a dozen in the United States. The genus, with pinguicula and one other little known genus, forms what most botanists call the family lentibulacece (from lentibula, an old name for one species), but Hooker in his edition of Maout and Decaisne (" General System of Botany") gives the family the more appropriate name utriculariece; its affinities as to the structure of the flowers are with the figworts (scrophulariacece), and that of the fruit with the primroses (primulacece). A few of our species are found rooting in the muddy or sandy margins of ponds; these have minute awl-shaped leaves, and a slender stem hearing a solitary flower or a few flowers. The majority of them are floating aquatics, and are usually without roots; their branching stems are furnished with leaves divided into fine, capillary segments, hearing numerous small bladders, which at flowering time enable the plant to float near the surface and throw up its naked stems, which bear a few yellow or purplish flowers.
The calyx is two-lipped; the monopetalous corolla two-lipped with a projecting palate, which often closes the throat; stamens two, with one-celled anthers; pistil with a one-celled free ovary, ripening into a several-seeded capsule. - The bladderworts have long been favorite plants with botanists, on account of their peculiar structure and the rarity of some of the species, but of late they have been invested with new interest from the fact that they must now be classed, with the closely related pinguicula, among insectivorous plants. It had been observed that the little bladders, which form such a striking feature of the floating species, contained minute crustaceans and other microscopic animals, and that their use was not solely, as had been supposed, to enable the plant to float and lift its flowers above the water. These hints induced Darwin to investigate the matter, and the results form two important chapters in his "Insectivorous Plants" (1875). About the same time Mrs. Mary Treat of Vineland, 1ST. J., investigated the subject, and though most of her observations (published in the " New York Tribune," January, 1875) were anticipated by Darwin, she noticed some points that escaped him, which he quotes in the work referred to.
Darwin's observations were made upon U. neglecta, which English botanists now regard as a subspecies of U. vulgaris, our most abundant bladder wort. The structure and action of the bladders require several pages and engravings for a full explanation. The bladders, of which there are two or three on the same divided leaf, are about one tenth of an inch across, and usually filled with water, though often containing bubbles of air; they are attached to the leaf by a short stalk, and, as shown by the enlarged engraving, are of a one-sided eggshape. The mouth or opening usually points downward, and on the upper side terminates in two long appendages, each of which bears six or seven long bristles; these appendages, of which that on the near side only is shown in the engraving, Darwin terms antenn0µ; beneath these is the opening, with several other bristles on each side of it, and this is closed by a valve so arranged that it can only open inward; this valve is furnished with numerous glands, and the whole interior of the bladder is studded with processes, consisting of four unequal arms, which he calls quadrifid processes.
The valve yields to a slight exterior pressure, the structure of the bladder being that of an admirably contrived trap for capturing microscopic creatures; and that it performs this office most effectively, the presence of animals or their remains in nine out of ten of the bladders is a proof. These creatures have been repeatedly seen by Mrs. Treat to enter the bladder, and she noted the time they remained alive after their capture; in most cases the before clear and transparent bladder became in less than two days so muddy from the decomposition of the animals that the contents could not be seen. Darwin has satisfied himself by experiments, given at length in the work referred to, that the utricularias capture these animals for nutriment.
Utricularia. Small branch with divided leaves and bladders, enlarged twice; a single bladder, greatly enlarged.
Common Bladderwort (Utricularia vulgaris).