Source, Etc

Euonymus bark is the dried root-bark of the wahoo tree, Euonymus atropurpureus, Jacquin (N.O. Celastrineoe), a tall erect shrub with small dark purple flowers succeeded by crimson fruits; it is common in the eastern United States, extending westward to Wisconsin and southward to Florida. The root-bark is alone official, but the stem-bark also is collected.

Description

Euonymus root-bark occurs in small, more or less irregular quilled or curved pieces, not usually exceeding 8 cm. in length or 12 mm. in width. The outer layer is a soft, spongy, finely fissured cork, of a light ash-grey colour marked with darker lines or patches (due to adhering particles of earth) and occasional small transverse scars. The inner surface is of a pale tawny yellow or buff colour and nearly smooth; occasionally a thin shaving of pale yellow, dense wood adheres to it, indicating that the bark is separated with difficulty from the root.

It breaks with a very short fracture, and if the two pieces be separated very gently from one another delicate silky threads will be seen connecting them; these threads consist of a substance resembling caoutchouc or guttapercha which is secreted in laticiferous cells in the bast, and is found in all species of Euonymus.

Fig. 123.   Euonymus root bark. Transverse section. Magnified. (Planchon and Collin.)

Fig. 123. - Euonymus root-bark. Transverse section. Magnified. (Planchon and Collin).

The section, which is of a greyish white colour, exhibits, when moistened, a narrow whitish cork, a pale cortex, and darker bast.

The bark has a faint but characteristic odour recalling that of liquorice root, and a disagreeable and persistent, bitter, acrid taste.

Microscopical Characters

The transverse section exhibits a thick layer of narrow cork cells, a cortex containing abundant cluster crystals of calcium oxalate and a wide layer of secondary bast in which small cells filled with a granular substance are scattered. The bark contains no bast fibres or sclerenchymatous cells. The medullary rays are one cell wide.

The student should observe

(a) The spongy grey cork,

(b) The characteristic silky threads from the fractured surface,

(c) The bitter taste.

Constituents

A bitter, crystalline alcohol, euonymol (C21H30O4), has been isolated from it. From the resin (3.2 per cent.) contained in it the crystalline alcohols euonysterol, homoeuonysterol, atropurol and citrullol have been separated.

The bark also contains considerable quantities of dulcitol (dulcite), C6H8(OH)6, a hexatomic alcohol readily crystallising in large plates melting at 188.5°; it has a sweetish taste and has been found in a considerable number of plants. The presence of the crystalline glucoside euonymin has not been confirmed.

Uses, - Euonymin (the powdered extract) is an hepatic stimulant, direct cholagogue, and mild cathartic. It is used in constipation and in hepatic derangements.

Substitutes

The stem-bark, which, although not official, is a commercial article, occurs in long thin narrow strips; it has a dark greenish grey cork, green cortex, and fibrous bast; it is therefore easily distinguished from the root-bark.

Wafer Ash bark, Ptelea trifoliata, Linne (N.O. Rutaceoe) has been frequently mixed with or substituted for euonymus bark; it is thicker, bears long, transverse, whitish scars; medullary rays three cells wide; below the cork a layer of yellow sclerenchymatous cells; in the secondary bast large oleo-resin cells.