The Purging Buckthorn is distinguished by its stiff habit, and by some of the leaves being gathered into bundles at the ends of the shoots. The leaves are egg-shaped, with toothed edges, and of a yellowish-green tint, with short leaf-stalks. The yellowish-green flowers are very small, and will be found both singly and in clusters from the leaf-axils. There are a four-cleft calyx, four petals, four stamens, or four stigmas, for the sexes are usually on separate plants. The fruit is black, round, and about a quarter of an inch across, containing four stones. These so-called "berries" are ripe in September. Formerly they were much used as a purging medicine, but of so violent a character that their use has come to be discouraged, and the safer syrup of Buckthorn is prescribed instead. The juice of these berries is the raw material from which the artist's sap-green is prepared. It may be found in woods, thick hedgerows, and bushy places on commons southward of Westmoreland, showing a decided preference for chalky soils. In Ireland it only occurs rarely. [Illustration: _Pl. 88._ Breaking Buckthorn.] [Illustration: _Pl. 89._ Fruits of Purging Buckthorn.] [Illustration: _Pl. 90._ Fruits of Breaking Buckthorn.] [Illustration: Purging Buckthorn. A, flowers.] The Breaking Buckthorn (_Rhamnus frangula_) is also known as the Berry-bearing Alder, its leaves, with their lateral veins, presenting something of the appearance of the Alder. Its more slender stems are purplish-brown in hue, and _all_ the leaves are arranged alternately up the stems. The leaves further differ from those of _R. catharticus_ in having plain, un-toothed edges, and their veins parallel one to another. The flowers are similar in size to those of the other species, but are whiter, less yellow, fewer in number, and on longer stalks. The parts of the flower, too, are in fives instead of fours; and the "berry," though similar to the previous species, is much larger (half-inch diameter). In an unripe condition these fruits yield a good green dye, much used by calico printers and others. The wood made into charcoal is said to be the best for the purposes of the gunpowder makers, who know it by the name of Black Dogwood. The straight shoots of both species are used for forming walking and umbrella sticks, and those of longer growth for pea and bean sticks. The Brimstone butterfly (_Gonepteryx rhamni_) lays its eggs on the leaves of _R. frangula_, upon which the larva feeds. The name Buckthorn appears to be due to an ancient misunderstanding of the German name Buxdorn, which should have been translated Box-thorn. Wild Plums (_Prunus communis_).