Different Species of Rhubarb.
Linnæus has distinguished the different species of rhubarb by the names Rheum Palmatum, R. Rhaphonticum,[183] R. Rhabarbarum, R. Compactum, and R. Ribes.
Botanists have long differed in their opinions, which of these several species is the true rhubarb; and that question does not appear to be as yet satisfactorily cleared up. |Rheum Palmatum.| However, according to the notion which is most generally received, it is supposed to be the Rheum[184] Palmatum; the seeds of which were originally procured from a Bucharian merchant, and distributed to the principal botanists of Europe. Hence this plant has been cultivated with great success; and is now very common in all our botanical gardens. The learned doctor[185]Hope, professor of medicine and botany in the university of Edinburgh, having made trials of the powder of this root, in the same doses in which the foreign rhubarb is given, found no difference in its effects; and from thence conclusions have been drawn with great appearance of probability, that this is the plant which produces the true rhubarb. But this inference does not appear to be absolutely conclusive; for the same trials have been repeated, and with similar success, upon the roots of the R. Rhaponticum and R. Rhabarbarum.
R. Rhaponticum.
The leaves of the R. Rhaponticum are round, and sometimes broader than they are long. This species is found abundantly in the loamy and dry deserts between the Volga and the Yaik[186], towards the Caspian Sea. It was probably from this sort that the name Rha, which is the Tartarian appellation of the river Volga, was first applied by the Arabian physicians to the several species of rheum. The roots however which grow in these warm plains are rather too astringent; and therefore ought not to be used in cases where opening medicines are required. The Calmucs call it Badshona, or a stomachic. The young shoots of this plant, which appear in March or April, are deemed a good antiscorbutic; and are used as such by the Russians. The R. Rhaponticum is not to be found to the West of the Volga. The seeds of this species produced at Petersburg plants of a much greater size than the wild ones: the leaves were large, and of a roundish cordated figure.
R. Rhabarbarum.
The R. Rhabarbarum grows in the crevices of bare rocky mountains, and also upon gravelly soils: it is more particularly found in the high vallies of the romantic country situated beyond Lake Baikal. Its buds do not shoot before the end of April; and it continues in flower during the whole month of May. The stalks of the leaves are eaten raw by the Tartars: they produce upon most persons, who are unaccustomed to them, a kind of sphasmodic contraction of the throat, which goes off in a few hours; it returns however at every meal, until they become habituated to this kind of diet. The Russians make use of the leaves in their hodge-podge: accordingly, soups of this sort affect strangers in the manner above mentioned. In Siberia the stalk is sometimes preserved as a sweet-meat; and a custom prevails among the Germans of introducing at their tables the buds of this plant, as well as of the Rheum Palmatum, instead of cauli-flower.
R. Rhaponticum.
The R. Rhaponticum which commonly grows near the torrents has, as well as the R. Rhabarbarum of Siberia, the upper part of its roots commonly rotten, from too much moisture: accordingly, a very small portion of the lower extremity is fit for use. The Russian College of Physicians order, for the use of their military hospitals, large quantities of these roots to be dug up in Siberia, which are prescribed under the name of rhapontic. But the persons employed in digging and preparing it are so ill instructed for that purpose, that its best juices are frequently lost. These roots ought to be drawn up in spring, soon after the melting of the snows, when the plant retains all its sap and strength; whereas they are not taken out of the ground before August, when they are wasted by the increase of the stem, and the expansion of the leaves. Add to this, that the roots are no sooner taken up, than they are immediately sliced in small pieces, and thus dried: by which means the medicinal qualities are sensibly impaired.