Rhubarb, or Rheum, L. a genus of exotic plants, comprising seven species, of which the following are the principal:

1. The rhaponticum, or Common Rhubarb, a native of Thrace and Syria, which has long been cultivated in British gardens for the footstalks of the leaves, that are frequently used in pics and tarts. The root of this species is sometimes mistaken for the officinal rhubarb, from which it differs materially ; as the surface of the former is of a dusky colour, its texture is more porous or spongy, and it possesses greater astringency than the later, but is less purgative, re-quiring two or three drams, instead of fifteen or twenty grains of the powder, for one dose.

2. The palmatum, Palmated, True or Officinal Rhubarb, is a native of China and the East Indies, whence its culture has been introduced into Europe. It produces a thick fleshy root, externally yellowish-brown, but internally of a bright-yellow colour, streaked with red veins; and it en-dures the severity of our climate.

The officinal rhubarb is raised from seed, which should be sown early in February, in light, sandy soils, that have been previously ploughed to a considerable depth, and manured with a compost, consisting of one part of rotten dung, one part of sifted coal-ashes, and two parts of slaked lime, thoroughly incorporated with a proper quantity of mud, or mire taken from a mill-pond.- This .species is also propagated, by planting buds or eyes in land thus prepared; which method is far superior to that before described ; as a whole year is not only gained in the growth, but the plant is less liable to be injured by the depredations of vermin; and, in the course of four or five years, the crowns of the rhubarb will produce tolerably good roots; which, however, are neither so large nor so plentiful as those obtained from seed.

When the plants appear above ground, they will only require to be kept clear from all weeds; and, if the roots be covered with litter, or the earth be drawn around them, in the winter, they will vegetate with renewed vigour in the spring. Should they grow too closely toge-ther, it will be necessary to thin them, at the distance of five, or six feet; and, at the expiration of four years, the roots may be taken up for use ; though their medicinal properties are supposed to increase, if they be suffered to remain in the earth for seven, eight, ten, or even twelve years.

The proper time for taking up the roots, in England, is from the middle of the summer to January; though they are sometimes dug out of the ground early in the spring; or in autumn, when the leaves are decayed. They are first washed clean, and the small fibres and external rind being pared or cut off, they are divided into pieces about one ounce in weight. In warm weather, they should be dried in the shade; but, if the season be cold or wet, it will be advisable to evaporate their moisture gradual- ly in a hot-house, or an oven of a moderate, heat; because, if dried too speedily, they will contract into wrinkles, and, if too slowly, they become mouldy, and unfit for use. Justly, a hole is perforated in the middle, and the roots are suspended on packthread to dry, so that none of the pieces come in contact with each other.

The rhubarb, hitherto employed in medicine, is imported from Turkey, Russia, China, and the East Indies. The first sort is brought in roundish pieces, perfo-rated in the centre; and which are externally of a yellow colour ; but, on being cut, they appear varie-gated with bright-reddish streaks. The Chinese drug is imported in long pieces, which are harder and more compact than the Turkey Rhubarb; the former, possessing a weaker aromatic flavour, is less esteemed ; though, being more astringent, it is, for some purposes at least, equal to the latter.

Rhubarb is justly prized as a mild cathartic, and may be safely administered to children, invalids, and delicate women, in doses of from 10 to 20 grains, though, in irritable, hysterical, and phthisical habits, it is apt to occasion gripes, and to aggravate febrile symptoms: hence it ought never to be given in the first stage of dysentery, when this invaluable remedy, by premature use, may occasion the most violent pain and inflammation of the bowels ; but, after the fever is suppressed, and the disease becomes a chronic diarrhoea, small doses of rhubarb will be attended with the best effects. As, however, this medicinal root has a tendency to occasion obstructions of the intestines after copious evacuations, it will, in most cases, be proper to combine it with cooling salts, in order to prevent costiveness : thus, Ograins of the former, and one dram of either Glauber's salt, or cream of tartar, in a combined state, may be taken with advantage in the evening, and a similar dose in the morning. In short, rhubarb is the only purgative we possess, that is at the same time mildly astringent, diuretic, and does not relax the first passages.

Being an article of such importance in medicine, large quantities of this root are annually imported, to the amount of 200,0001; which sum might easily be saved to the Nation :various attempts have, therefore, been successfully made to introduce its culture into Britain. With this intention, the patriotic Society for the Encouragement of Arts, etc have, for several years, distributed premiums for the cultivation and curing of the largest quantity of rhubarb. The successful candidates were, Sir William Fordyce, on whom they confer-red a gold medal in 1784; Mr. Thomas Jones, whom they rewarded with a similar premium in 1793, and with the farther sums of 30 guineas in 1798, and 1800; Mr. Hayward, on whom they conferred their gold medal in 1794; Mr. Ball, to whom they adjudged a similar reward in the same year, and a second in 1795; Mr. Robert Davis, and the Rev. James Stillingfleeft, on whom they severally bestowed gold medals in 1796 in 1797, for their respective exertions in cultivating and curing the true rhubarb. Their methods of management correspond, with a few exceptions, to that above stated ; and it appears from authentic accounts, that sufficient quantities of this valuable drug may be reared in Britain; and that the English root has proved to be fully equal to the best sort obtained from Turkey and China.

Beside the utility of the roots, the seeds of such plants as are raised in England, possess a considerable portion of the medicinal properties of the former : its leaves impart an agreeable acidity to soups, similar to that of sorrel: a strong infusion in white wine, of pieces of the roots, that were not sufficiently thick for drying, has been given with great success in the dysenteries sometimes incident to cattle. - A marmalade is likewise prepared from the fresh stem, by stripping off the bark, and boiling the pulp with an equal quantity of honey or sugar. This, we understand, affords a mild and pleasant laxative, especially for children, to whom it is highly salubrious.-Lastly, Prof. Pallas informs us, that M. SIeverS, an apothecary, has discovered a resinous elastic gum, which, in the month of August, exuded from the leaves and flower-stalks of the Siberian rhubarb, on wounding them with a knife ; and which bore perfect resemblance to the Caoutchouc, or India rubber.- By a decoction of this root in alum-water, the Kirghis impart a beautiful orange colour to their leather and wool: a similar tint may be given to cloth; and, on adding green vitriol, a fine olive shade will be the result. - It has farther been conjectured, that, with a solution of tin, or bismuth, rhubarb would afford a beautiful red dye.