ALDER BUCKTHORN 245 



The traverse section shows under the lens a narrow dark purple 

 cork and yellowish brown cortex and bast. 



Older bark is commonly much rougher. It has usually a dull 

 dark purple colour, and is marked with transversely elongated lenticels 

 and shallow longitudinal fissures, the cork exhibiting less disposition 

 to exfoliate. The transverse section shows a similar purple cork ; 

 the bast is thicker and allows of "very thin medullary rays being 

 distinguished. The absence of sclerenchymatous cells is a character 

 occasionally of value in excluding substitutes. 



The bark has no odour and a taste that is scarcely bitter. 



The student should observe 



(a) The dark purple cork, showing, when scraped, a deep crimson 



colour, 



(6) The light-coloured lenticels, 

 (c) The shortly fibrous fracture of the bast. 



FIG. 125. Alder Buckthorn bark. Trans- 

 verse section. Magnified. (Berg.) 



Microscopical Characters. A transverse section exhibits a cork consisting 

 of narrow cells many of which contain a bright purplish crimson colouring 

 matter. The cortex contains small starch grains, cluster-crystals of calcium 

 oxalate and elongated mucilage cells, but no sclerenchymatous cells. The 

 secondary bast contains numerous tangentially elongated groups of thick-walled 

 bast fibres ; the medullary rays are mostly two cells wide. The cells of the 

 medullary rays and bast parenchyma contain a yellowish amorphous substance 

 dissolving in solution of potassium hydroxide with production of a bright purple 

 colour. 



Constituents. The active constituents of alder buckthorn bark 

 are but imperfectly known. It contains a glucoside, frangulin, 

 C 21 H 20 9 , which crystallises in lemon-yellow needles melting at 228 

 to 230, is slowly volatile at ordinary temperature and stains the 

 paper in which the drug is kept ; it is soluble in caustic alkalies 

 with purple coloration. Boiled with alcoholic hydrochloric acid it is 

 converted into rhamnose and frangula-emodin. Rhamnose (isodulcite) 

 is a pentatomic alcohol (pentose, pentaglucose), and is produced by 

 the hydrolysis of quercitrin and a number of other glucosides, which 

 are therefore termed rhamnosides. Frangula-emodin, C 15 H 10 O 5 , occurs 

 in reddish yellow crystals melting at 254. It is a derivative of 

 anthraquinone, viz. trioxymethylanthraquinone, C 14 H4(CH 3 )(OH) 3 O 2 , 



