278 BARKS 



less flattened fibrous strips that are remarkable for their extreme 

 toughness and flexibility ; they can easily be torn lengthwise, but it 

 is almost impossible to break them. 



The outer surface (cork) is of a yellowish or olive brown colour, 

 very thin, and transversely wrinkled, that of the stem-bark being 

 marked with scattered rounded scars of leaves and buds, and often 

 bearing the minute black apothecia of small lichens. It easily sepa- 

 rates in papery fragments from the cortex, which is either green 

 (stem-bark) or yellowish (root-bark) in colour. The inner portion 

 of the bark (bast) has a pale yellowish or nearly white and silky inner 

 surface ; it is extremely tough and fibrous from the presence of 

 numerous strands of tough bast fibres. 





FIG. 138. Mezereon bark. Slightly reduced. 



The dry bark has little or no odour, but a persistent burning acrid 

 taste. So marked is the acrid nature of the bark that, moistened and 

 applied to the skin, it produces inflammation and even vesication. 



Spurge laurel bark is very similar to the foregoing ; it may be 

 distinguished by the purplish grey colour of the cork and by elongated, 

 pointed oval leaf- and bud-scars which are crowded at intervals. 



The bark of D. Gnidium has a dark purplish brown cork ; the leaf- 

 scars resemble those of D. Mezereum. 



The student should observe 



(a) The thin, easily separable cork, 



(b) The silky inner surface, 



(c) The extreme toughness and flexibility. 



Constituents. Mezereon bark contains a greenish brown amorphous 

 resin, mezerein, possessing extremely acrid and sternutatory 

 properties. It easily changes into an acid bitter resin, mezereic acid, 

 which is present in the ethereal and alcoholic extracts of the bark. 



