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SCIENTIFIC AND APPLIED PHARMACOGNOSY 



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 glucosidal 

 tannoid constituents are also present: glucogallin, yielding gallic 

 acid, and tetrarin, yielding in addition to gallic acid, cinnamic acid 

 and rheosmin, an aldehyde having the odor of rhubarb. A catechin 

 resembling the catechin of gambir has also been found. Rhubarb 

 also contains considerable starch; calcium oxalate; and yields about 

 15 per cent of ash. 



FIG. 82. Rhubarb: C, rosette aggregates of calcium oxalate; P, parenchyma 

 containing starch grains (S); T, tracheae; E, sieve; R, reddish-brown amor- 

 phous masses separated from the resin or tannin cells. 



Rhubarb leaves contain oxalic acid and cases of poisoning are 

 recorded from their consumption. (Jour. A. M. A., 1917, p. 1954). 



Allied Plants. The rhizomes of other species of Rheum are also 

 used to a limited extent, as English or Austrian rhubarb from Rheum 

 rhaponticum; they are more or less cylindrical, distinctly radiate, 

 and contain, besides chrysophanic acid, rhapontin. Rheum palma- 

 tum, which is cultivated in France, Germany and Russia, produces 

 rhizomes that are lighter in color and less valuable than the Chinese 

 rhubarb, the constituents being similar to those of Austrian rhubarb. 



Rhapontic rhubarb contains a crystalline glucoside rhaponticin, 

 which is colored purplish-red with sulphuric acid, changing to orange. 



