298 



RHAMNACE^: 



section shows numerous thin, almost straight, broadening medullary 

 rays, which run on an average about three-fourths of the distance 

 across the bark. Medullary rays in groups converging at their outer 

 ends (distinction from Rhamnus Calif arnica) ; stone cells present (dis- 

 tinction from Rhamnus frangula). If to a small quantity of the 

 powdered barks an alkaline solution be added, the color developed 

 in the Rhamnus Californica is a deep red, while that of R. Purshiana 

 is orange. Odor distinct; taste bitter and slightly acrid. 



Powder. Characteristic elements of: See Part iv, Chap. I, B. 



FIG. 170. Rhamnus purshiana Branch. 



CONSTITUENTS. Emodin and frangulic acid; frangulin and purshianin 

 the two latter being glucosides, yielding, on hydrolysis, emodin and 

 sugar. The principle, emodin, is found in many purgative drugs. 

 Its composition, and its relation to several carbon compounds are 

 shown in the following: 



Anthracene 



Anthraquinone 



C 14 H 6 (OH) 2 2 



Chrysophanic Acid 



C 14 H4CH,(OH),Oi 



Emodin 



Emodin is, therefore, said to be a trioxy-methyl-anthraquinone. It 

 is contained in rhubarb, senna, aloes, etc. See emodin test under Rhu- 

 barb (120). The resins are turned a vivid purple-red by caustic potash. 

 The fresh bark is active as a purgative, causing much griping. By 



