280 BARKS 



Description. Cascarilla bark is usually imported in single quills 

 or channelled pieces, commonly varying from 5 to 10 cm. in length 

 and from 4 to 6 mm. in width, rarely exceeding the latter limit. The 

 outer layer of the bark is a white or greyish white cork which owes 

 its characteristic chalky appearance to the presence in the cells of 

 numerous crystals of calcium oxalate. It is longitudinally wrinkled, 

 and often, at more distant intervals, both longitudinally and trans- 

 versely furrowed, thus assuming a chequered appearance. It 

 frequently bears the minute black apothecia of a small lichen, and 

 easily exfoliates, disclosing a brown or dark grey inner layer (cortex) 

 marked with furrows corresponding to those in the cork. On some 

 portions of the bark the white cork is so thin that the brown cortex 

 shows through and imparts to the outer surface a brown or dark 

 grey colour. 



The inner surface of the bark is dark in colour and longitudinally 

 striated. The fracture is short and resinous. The section exhibits 



under the lens a pale cork layer and 

 a dark brown cortex and bast, the 

 latter being traversed by numerous 

 very thin whitish medullary rays. 



Microscopical Structure. A transverse 

 section of cascarilla bark, examined under 

 FIG. 140.-Cascarilla bark. Trans- the micr scope, exhibits a cork of vary- 

 verse section. Magnified. (Berg.) m g thickness, the cells of which have 



thickened outer but thin inner walls ; in 

 the latter, numerous minute crystals of 



calcium oxalate are embedded. Some of the cells of the cortex contain 

 prismatic or cluster-crystals of calcium oxalate, others (secretion cells) droplets 

 of oleo-resin. The bast contains in addition small scattered groups of small 

 (not over 26/x wide) bast fibres together with numerous cells filled with a 

 brown amorphous substance, but neither bast nor cortex contains any cells with 

 thickened lignified walls. These characters are useful in distinguishing cascarilla 

 bark from various barks that have been substituted for it. 



The bark has a pleasant aromatic colour and an aromatic but rather 

 disagreeably bitter taste. When burned it exhales an agreeable odour, 

 whence its use as an addition to fumigating mixtures, tobacco, &c. 

 It yields about 8 per cent, of ash, but sittings may yield much more, 

 probably because they contain many cork fragments rich in calcium 

 oxalate. 



The student should observe 



(a) The chalky cork, 



(b) The longitudinal wrinkles and longitudinal and transverse 



fissures, 



(c) The short resinous fracture and the appearance of the section 



under the lens, 



(d) The aromatic odour and bitter taste. 



