knot-grass; a genus of the trigynia order, belonging to the otiandra clas of plants. There are 27 species; but the most remarkable are:

1. The bittora, bittor, or greater snakeweed, hath a thick oblique intorted root; blackish without and red within; a simple round slender stem near two feet high; oval leaves, having recurved foot-stalks, and the stalk terminated by thick short spikes of whitish-red flowers.

2. The vivaparum, or smaller bittor, hath a thickish root, a simple slender stem half a foot high, spear-shaped leaves, and the stalks and branches terminated by long spikes of whitish-red flowers. Both these perennials flower in May and June, succeeded by ripe seeds in August. They grow wild in England, &c. The first in moist places, the other in mountainous situations.

3. Oriental polygonum, commonly called persicaria, hath fibrous roots; an upright, robust, strong, jointed stem, rising eight or ten feet high, dividing at top into several branches; very large oval-lanceolate alternate leaves, on broad foot-stalks half surrounding the stem; and all the branches terminated by long, slender, hanging spikes of reddish-purple heptandrous and digynious flowers, from July till October.

4. Fagopyrum, buckwheat, or braek, rises with an upright smooth branchy stem, from about a foot and a half to a yard high, heart-shaped sagittate leaves, and the branches terminated by clusters of whitish flowers, succeeded by large angular seeds; excellent for feeding pigeons, and most sorts of poultry.

All these plants are hardy, and succeed in almost any soil and situation; the two first are perennial in root; and the third and fourth are annual, wholly decay at the end of summer, or early in winter. The first two sorts are retained in some curious gardens for variety; but their chief merit is for medical purposes: they are powerful astringents, and are used both internally and externally; esteemed very efficacious in hemorrhages, and other fluxes; and good to heal sore mouths. Third sort, Oriental polygonum, or persicaria, is a most elegant annual for the embellishment of the pleasure-ground; assuming a majestic tree-like growth by its erect luxuriant stem, and branchy head; which being garnished with noble large foliage, and numerous pendulous spikes of flowers, in constant succession three or four months, exhibits a very ornamental appearance from June or July until October, and is so easy of culture, that from its scattered seeds in autumn, young plants rise spontaneously in abundance the ensuing spring, and shoot up so rapidly as to attain six or eight feet stature by July, when they generally begin flowering, and continue till attacked by the frosts, then totally perish; so that a fresh supply must be raised from seed annually. The fourth sort (buck-wheat) is a sort of corn, and is frequently cultivated both by way of fodder, cutting its stalks while young and green to feed Polygonum feed cattle; and for its grain to feed pigeons, poultry, hogs, &c. It flourishes in any soil and situation, but generally thrives best in a light dry earth; and the driest seasons seldom retard its growth. The first and second sort are easily propagated in plenty, by parting the roots in autumn. The third sort, Oriental polygonum, being annual, is always propagated from seed annually, either in the full ground, or by aid of hot-beds.

Uses. The root of a kind of biftort, according to Gmelin, is used in Siberia for ordinary food. This species is by Haller called biftorta foliis ad oram nervosis, and by some other botanists biftorta montana minor. The natives call it moska; and so indolent are they, that, to save themselves the trouble of digging it out of the earth, they go in spring and pillage the holes of the mountain rats, which they find filled with these roots. In our country, biftort is used in medicine. All the parts of biftort have a rough astringent taste, particularly the root, which is one of the strongest of the vegetable astringents. It is employed in all kinds of immoderate hemorrhages and other fluxes, both internally and externally, where astringency is the only indication. It is certainly a very powerful astringent, and is to be looked on simply as such; the sudorific, antipellitential, and other like virtues ascribed to it, it has no other claim to, than in consequence of its astringency, and of the antiseptic power which it has in common with other vegetable astringents. The largest dose of the root in powder is one dram.