476 BOTANY AND PHARMACOGNOSY. 



perforated, strung on ropes and dried either in the sun or by 

 artificial heat. The drug is exported chiefly from Shanghai. The 

 principal commercial varieties are known as Chinese rhubarb, 

 Canton rhubarb and Shensi rhubarb, the latter being preferred. 



Description. Cut into irregular plano-convex and oblong 

 pieces, frequently with a large perforation, hard and moderately 

 heavy, 5 to 15 cm. long, 5 to 8 cm. broad and 3 to 6 cm. thick; 

 externally mottled from alternating striae of light-brown paren- 

 chyma cells and dark-brown medullary rays, occasionally with 

 reddish-brown cork patches and small radiate scars of fibro- 

 vascular tissue, smooth and sometimes covered with a light-brown 

 powder ; fracture somewhat granular ; internally light brown ; odor 

 distinct ; taste bitter, astringent and gritty. 



Light and spongy rhizomes should be rejected. 



Inner Structure. See Figs. 281, A; 289. 



Constituents. The principal constituent appears to be a 

 glucoside (possibly the chrysophan of some authors) or an unde- 

 termined substance which yields successive oxidation products, 

 viz.: chrysophanic acid (di-oxy-methyl-anthraquinone), emodin 

 (tri-oxy-methyl-anthraquinone), and rhein (tetra-oxy-methyl-an- 

 thraquinone). Chrysophanic acid crystallizes in golden-yellow, 

 clinorhombic prisms and dissolves in alkalies and in concentrated 

 sulphuric acid, the solutions having a deep-red color. It is 

 re-formed in rhubarb after extracting it by exposing the moistened 

 root to air. Emodin occurs to the extent of 1.5 per cent, and 

 forms orange-red needles which are soluble in hot toluene and 

 give with alkalies and alkali carbonates purplish colored solu- 

 tions. RiiEiN forms yellowish-brown scales which are insoluble 

 in hot toluene, soluble in hot acetic acid and produce purplish-red 

 solutions with the alkalies or alkali carbonates. Recently another 

 oxymethylanthraquinone-yielding substance, rheopurgarin, has 

 been isolated from Shensi rhubarb. It forms yellow needles, and 

 appears to be composed of four glucosides : (a) one related to 

 emodin, (b) one related to rhein, (c) chrysophanein, which 

 yields chrysophanic acid, and (d) rheochrysin, which yields a 

 yellow crystalline body, rheochrysidine, considered to be identical 

 with Hesse's rhabarberon or iso-emodin. The following glu- 

 cosidal tannoid constituents are also present : glucogallin, yield- 

 ing gallic acid, and tetrarin, yielding in addition to gallic acid. 



