POLYGONACEJE. 481 



its double twist, contains much tannin, some gallic acid and starch, and 

 is a powerful astringent. The leaves of P. Hydropiper, Water-pepper, 

 are acrid and vesicant. P. tinctorium yields a blue dye. The fruit of 

 P. aviculare is emetic and purgative. The fruit of Fagopyrum esculen- 

 tum, and other species of Buckwheat, is used as food. The plant is 

 cultivated in some northern countries. The leaves of Rumex Acetosa, 

 Common Sorrel, and of R. Acetosella, Field Sorrel, are acid and astringent. 

 The roots of Rumex aquations, Water Dock, R. Hydrolapathum, Great 

 Water Dock, and of other species, are used as astringents and alter- 

 atives, while those of R. alpinus, under the name of Monk's-rhubarb, 

 were formerly employed as purgatives. One of the most important 

 plants of the order is the Rhubarb-plant. The officinal rhubarb is 

 the root of an undetermined species of Rheum. The extent of country 

 from which rhubarb of one kind or another is actually collected, 

 according to Christison, stretches from Ludak, in 77^ east longitude, 

 to the Chinese province of Shen-si, 29 farther east, and from the 

 Sue-chan mountains, in north latitude 26, nearly to the frontiers of 

 Siberia, 24 northward. The best rhubarb is said to come from the 

 very heart of Thibet, within 95 east longitude, and 35 north latitude, 

 five or six hundred miles north of Assam. The following are the 

 species of Rheum said to yield rhubarb: 



1. Rheum. Palmatum. L. This has perhaps the best title to be considered the 



true rhubarb-plant. 



2. Rheum undulatum, L., which yields much of the French rhubarb. 



3. Rheum Compactum, L. Another species yielding French Rhubarb, and 



often cultivated in Britain for its acid petioles. 



4. Rheum Emodi, Wall. This species yields a kind of Himalayan rhubarb. 



Its petioles are used for their acid properties. 



5. Rheum rhaponticum, L. Used in France and Britain in the same way as 



the third species. 



6. Rheum hybridum, Murr. Much cultivated in Germany for its root, and in 



Britain for its stalks. 



7. Rheum Webbianum, Eoyle. A Himalayan species. 



8. Rheum spiciforme, Royle. Another Himalayan species. 



9. RJieum Moorcroftianum, Royle. Another Himalayan species. 



10. Rheum crassinervium, Fisch. A Russian species. 



11. Rheum leucorhizum, Pall. A Siberian and Altai species, said to yield 



imperial or white rhubarb. 



12. Rheum Capsicum, Fisch. A Caspian and Altai species. 



13. Rheum Ribes, L. An Affghanistan and Persian species. 



All these species 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 Eussian or Turkey, Chinese or 

 East Indian, and English rhubarb. Rhubarb contains raphides of oxa- 

 late of lime (If 18), along with tannin, gallic acid, resin, and a peculiar 



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