POLYGO'NEE, or POLYGONACE1E, a natural order of exogenous plants, mostly herba ceous plants, but including a few shrubs, and even trees. The leaves are alternate, sometimes without stipules, hut more generally with stipules cohering around the stem. The flowers are not unfrequently unisexual. They have an inferior, often colored peri anth, generally in four, five, or six segments; three to nine stamens inserted into the bottom of the perianth; a one-celled ovary, usually formed of three carpels, but con taining only one ovule; styles and stigmas as many as the carpels of the ovary: the fruit generally a nut, often triangular, the seed with farinaceous albumen, which has an economic importance in buckwheat. A few species produce a succulent edible fruit. The order contains nearly 500 known species, natives of almost all parts of the world, but particularly abundant in the temperate regions of the northern hemisphere. Many of the species are common weeds in Britain, as different species of dock (q.v.) and ray rionunz. Bistnrt (q.v.), buckwheat (q.v.), and sorrel (q.y.) belong to this ordcr.—The genus pon,yonum, has a colored perianth of five segments. stamens in two rows, styles more or less united at the base, and two or more in number; the fruit invested by the persistent perianth. The species are very numerous. A number are natives of Britain. KNOT-GRASS (P. ariculm'e), a very common British weed, is one of the plants remark able for most extensive distribution over the world. It is an annual of very humble growth, but very variable, with much branched trailing stems, small lancelate leaves, and very small flowers, two or three together, in the arils of the leaves. Thunberg says that in .Japan a blue dye is prepared from the plant. P. amphibiam, one of the species often called pereicaria, is abundant about margins of ponds and ditches in Britain and throughout Europe, and is remarkable for the difference between the leaves which float on the water, as is often the case, and those on stems growing erect, those of the former being broad and smooth, those of the latter narrow and rough; the spikes of flowers being also of somewhat different form, and the stamens in the flowers of the floating stems shorter than the perianth, in the upright stems about as long as the perianth; differences which might be held to indicate different species, yet both may be found growing from one root. The stems have been used on the continent of Europe as a sub
stitute for sarsaparilla. Some other species are occasionally used for medicinal pur poses. P. kydropiper, often called WATER PEPPER, a plant common by sides of hikes and ditches in Britain, is acrid enough to be used as a vesicant. Several species are occasionally used for dyeing. as the SPOTTED PEI:SWARM (P. persicaria), a very com mon weed on dunghills and in waste places in Britain; but the only species really important on this account is that called DYERS' BUCKWHEAT (P. tinetariune), a native of China, biennial, with ovate leaves and slender spikes of reddish flowers, the cultivation of which has been successfully introduced in France and Flanders. It yields a blue dye scarcely inferior to indigo.—P. orientate has long been occasionally cultivated in flower gardens in Britain, and is quite hardy, although a native of the West Indies.—Iirgopy ram cyntosant, a species of buckwheat abundant on the mountains of the n. of India, affords an excellent substitute for spinach.— Mahlenbeckia adpresga is the Maequarrie Harbor vine of Tasmania, an evergreen climbing or trailing shrub of most rapid growth, sometimes 60 ft. in length. It produces racemes of fruit somewhat resembling grapes or currants, the nut being invested with the large and fleshy segments of the calyx. The fruit is sweetish and sub-acid, and is used for tarts. Coccolsbit urzfera is the SEA-SIDE GRAPE (q.v.) of the West Indies. See also Cafimooxum.