JOHN's-WORT, or Saint John's-wort, Hypericum, L. a genus of plants comprising sixty-three species, nine of which are natives of Britain. Of these, the principal is the perforatum, Common, or Perforated Saint John's-wort, growing to the height of eighteen inches, in thickets, woods, hedges and on dry banks: it flowers in the months of July and August.
This plant is eaten by goats, cows, and sheep, but is refused by horses and hogs. Its medicinal virtues are not accurately determined. The leaves, however, when given in substance, are said to destroy worms; and the semi-pellucid dots found on them, yield, on distiliation, an essential oil. In Sweden, the flowers are used to impart a purple tinge to spirits; and the whole plant, when dried, and boiled in alum-water, communicates yellow or brown-red shades to yarn. The seed-bearing tops contain a fine red colour, that appears on friction between the fingers, and more than any other vegetable, resembles the gum-lac.