Rhubarb.—­This most important plant belongs to the genus Rheum.  The officinal rhubarb is the root of an undetermined species.  There are about thirteen different kinds which are said to yield rhubarb.  Lindley enumerates fifteen.  I however take Professor Balfour’s classification:—­

    1. Rheum palmatum, native of Bucharia, which has perhaps the best
    title to be considered the true rhubarb-plant, grows spontaneously
    in the Mongolian empire on the confines of China.

    2. R. undulatum, native of China, which yields much of the French
    rhubarb.

    3. R. compactum, native of Tartary, another species yielding
    French rhubarb, and often cultivated in Britain for its acid
    petioles.

    4. R.  Emodi (Wallich).  This species yields a kind of Himalayan
    rhubarb.  Its petioles are much used for their acid properties.

    5. R.  Rhaponticum, native of Asia.  Used in France and Britain in
    the same way as the third species.  It is much cultivated in the
    department of Morbihan.

    6. R. hybridum (Murr).  Much cultivated in Germany for its root and
    in Britain for its stalks.

    7. R.  Webbianum (Royle). 8. R.  Spiceformi (Royle). 9. R. 
    Moorcroftianum (Royle).  Himalayan species or varieties.

    10. R. crassinervium (Fisch), a Russian species.

    11. R. leucorhizum (Pall), a Siberian and Altai species, said to
    yield imperial or white rhubarb.  It has striped flowers, while all
    others are whitish green.

    12. R.  Caspicum (Fisch), a Russian and Altai species.

    13. R.  Ribes, native of the Levant, but some say an Afghanistan or
    Persian species.

All these grow in the cold parts of the world, as on the Altai mountains, in Siberia, Thibet, North of China, and on the Himalayan range.  The rhubarb procured from one or more of these species is known in commerce under the names of Russian or Turkey, Chinese or East Indian, and English rhubarb.

The plants all thrive well in a rich loamy soil, or light sandy soil, and are increased by divisions of the roots or by seed.

The extent of country from which rhubarb of one kind or another is actually collected, according to Christison, stretches from Ludall, in 771/2 east longitude, to the Chinese province of Shen-si, 29 degrees further east, and from the Sue-chan mountains, in north latitude 26 degrees, nearly to the frontiers of Siberia, 24 degrees northward.  The best rhubarb is said to come from the very heart of Thibet, within 95 degrees east longitude and 35 degrees north latitude, 500 or 600 miles north of Assam.