POL'YGONA'CE1E (Neo-Lat. nom. pl., from Lat. polygon um, from Gk. voXeryovov, knot-grass, polygony, nett. sg. of pot ygonos, pro lific. from roX6s , pot ys. much, many + 76vor, go»os, seed), THE BUCEIVIIEAT FAMILY. A nat ural order of about 30 genera and 750 species of widely distributed dicotyledonous herbs, a few shrubs and trees, particularly abundant in the temperate regions of the Northern Hemisphere. The principal genera are Chorizant he. Eric gonum, Rumex, Rheum, Polyg,onuin, Fagopyrum, and Coccoloba. The genus Polygonum. which is typical of the order, consists of abut 150 species, mostly weeds. Knot-grass lure) is one of the most extensively distributed as positive; in Fig. 4, P has reached BC and the upper part of the polygon has become zero; in Fig. 5. P has passed through BC and the upper part of the figure has passed through zero and become negative.
The sum of the interior angles of a polygon plants of the world: it is an annual of low growth, but very variable, with much branched trailing stems, small lanceolate 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. Polygonum
amphibium, one of the species of the section or suborder Persicaria, is abundant about margins of ponds and ditches throughout the Northern Ifemisphere. It has two forms of leaves; those upon the erect stems being broad and smooth, those iNhiell float in the water narrow and rough, differences which might be held to indicate dis tinct species, yet both may be found growing from me root. The stems have been used on the Continent of Europe as a substitute for sar saparilla. Several species are occasionally used for dyeing, as the spotted persicaria (Polygonum Pcrsicaria), a very common weed on manure heaps and in places in Europe and also naturalized in the United States. The only spe cies really important on this account is that called dyers' buckwheat (Polygonum tineto rium), a Chinese biennial, with ovate leaves and slender spikes of reddish flowers. It has been successfully cultivated in Franee and Flanders. It yields a blue dye scarcely inferior to indigo. Coecoloba, another genus of this order, has a wide distribution throughout the tropics, roceoloba urifera and other species producing edible fruits.