364 SUBTERRANEAN ORGANS 



the secondary wood is the cambium, usually visible as a dark line, and 

 here and there are the narrow remains of the bark. Small cylindrical 

 pieces are generally more favourable for examination than flat slices 

 of a larger rhizome. 



The structure of this drug is complex, but it must be remembered 

 that it is a very fleshy rhizome, the internodes of which are so closely 

 approximated as to be almost suppressed. 



The drug possesses a characteristic odour and bitter, astringent 



FIG. 190. Chinese Rhubarb (Shensi flat). Flat (inner) surface 

 of a plano-convex piece, showing irregularly distributed 

 rT ' ' star-spots. (Planchon and Collin.) 



taste ; when chewed it is very gritty between the teeth, a character 

 due to the calcium oxalate, which occurs in considerable quantity in 

 large cluster-crystals. 



The student should particularly observe 



(a) The firm, compact, texture, 



(b) The outer surface, seldom much wrinkled, 



(c) The continuous ring of star-spots on the transverse section, 



(d) The network of white lines on the outer surface (not shown when 



the peeling has been carried too deep). 



Constituents. Rhubarb exerts an astringent and also a laxative 

 action. 



