From the Cashew nut tree a milky juice is obtained, by tapping or incision, which stains, of a deep black colour, whatever it touches. The fine black varnish so much used in China and Japan is the resinous juice of a tree called fsi-chu, which is conjectured to be the cashew nut tree.
TRIGYNIA.
134. The TRUE or OFFICINAL RHUBARB (Rheum palmatum) is a medicinal root which grows wild in various parts of Asia.
The leaves which issue from this root are large, and deeply cut into lobes; and the whole plant has a general resemblance to what in our country are called docks. The stem is erect and six or seven feet high. The leaves stand on footstalks, that are somewhat grooved above, and rounded at the edge. Those which proceed from the stalk supply at the joints a kind of membraneous sheaths. The flowers terminate the branches in clusters.
The importance and the properties of this root in medicine are universally known. Rhubarb is usually imported from Turkey, but it is occasionally also brought from Russia, China, and the East Indies. Dr. Woodville states that the Turkey rhubarb is brought over in oblong pieces, flattish on one side, and rounded on the other; and that it is compact, hard, heavy, and internally of a dull colour, variegated with yellow and white. The Chinese rhubarb is in roundish pieces, each with a large hole through the centre. It is softer than the former, and exhibits, when broken, many streaks of bright red colour.
In some of the mountains of Tartary, rhubarb plants are found in great abundance. The roots, when first dug out of the ground, are thick, fleshy, externally of yellowish brown colour, and internally of bright yellow streaked with red veins. When they have attained sufficient size, they are dug up and cleansed; and the small fibres and the rind being cut off, they are divided into pieces of proper size. Each piece is then perforated in the middle, and they are strung on cords in such manner as not to touch each other, and are suspended to dry, either upon adjacent trees, or in the tents.
The sum expended for the importation of this drug is said to exceed 200,000l. per annum, a great proportion of which, it is presumed, might be saved to the country by cultivation of the plants in Great Britain. This was first attempted, about sixty years ago, by Dr. Hope, in the botanic garden at Edinburgh, and with such success as to prove that the climate even of Scotland would be no obstacle to its increase. In 1791, Sir William Fordyce received from the Society for Encouragement of Arts, Manufactures, and Commerce, a gold medal, for having raised more than 300 plants of the true rhubarb from seed. And, in 1783, Mr. Davis, of Minehead, in Somersetshire, brought to perfection as many plants as yielded three hundred pounds' weight of dried rhubarb. Since this period, rhubarb has been grown, in different parts of England, to great extent; and has so far flourished, that some of the roots have weighed seventy pounds and upwards. The principal difficulty has attended the curing of it; but this, after numerous experiments, has at length been performed in such manner, that the English drug has been found equal, or nearly equal, to that which is imported from Turkey and China.
The bark of rhubarb has been used for tinctures, and found, in every respect, as efficacious as the best part of the roots: and the seeds possess nearly the same qualities. The leaves impart an agreeable acidity, somewhat similar to that of sorrel; and a marmalade, which may, with advantage, be adopted for children, is made from the fresh stalks, by stripping off the bark, and boiling the pulp with an equal quantity of sugar.
135. The COMMON RHUBARB (Rheum rhaponticum), is a plant which is cultivated in kitchen gardens, and has large, blunt and smooth leaves, and the leaf-stalks furrowed on the upper side, and rounded at the edge.
This species of rhubarb grows wild on the mountains of Rhodope, in Thrace, whence it was first propagated in other parts of Europe, about the year 1630. It is chiefly in request for the footstalks of the leaves, which are used, (in the early part of the year, when there is little fruit) for pies and tarts. The root has some of the qualities of the true rhubarb, and has occasionally been imposed upon purchasers for that drug.