CUSPARIA 239 



Description. Cusp ana bark occurs in somewhat thin curved or 

 channelled pieces or single quills, usually about 8 or 10 cm. long and 

 1*5 to 3 mm. thick, but sometimes much longer, one of the longitudinal 

 margins being frequently obliquely cut. The outer layer (cork) is 

 sometimes buff -coloured, friable, and easily removed by the finger-nail, 

 sometimes dark grey, thin and firmly adherent, a difference due to the 

 alternate production of layers of thin and thick-walled cork cells. 



Below the cork is a hard, dark brown middle layer (cortex), whilst 

 the inner surface of the bark (bast) is of a cinnamon or chocolate brown 

 colour and finely striated . This portion frequently exhibits a laminated 

 structure and bears numerous minute short white lines, longitudinally 

 arranged, which are usually easily visible under a lens, especially after 

 the inner surface has been smoothed with a knife. They are caused 

 by axially elongated cells filled with acicular crystals of calcium oxalate. 

 Similar white masses of calcium oxalate may be seen en the smoothed 

 radial and transverse sections. 



The fracture is short and resinous, the transverse section exhibiting 



FIG. 118. Cusparia bark, showing buff spongy cork and 

 obliquely cut edges. Natural size. 



a whitish cork, a yellowish brown cortex, and, in the bast, yellowish 

 oblique or wavy medullary rays alternating with darker bast-rays. 

 Throughout both cortex and bast numerous cells filled with white 

 crystals of calcium oxalate, as well as minute dark ones filled with oil, 

 may be distinguished under the lens. 



Microscopical Characters. A transverse section examined under the micro- 

 scope shows a cork varying in thickness and in the nature of the cells, layers 

 with thin-walled cells alternating with thick-walled. The primary cortex 

 usually contains but few sclerenchymatous cells ; when present they are generally 

 near the cork and probably belong to the phelloderm. The secondary bast 

 contains occasional tangentially elongated groups of bast fibres and slender 

 axially elongated prisms of calcium oxalate. All the tissues except the cork 

 contain small oil-cells with droplets of yellowish oil, and tangentially elongated 

 cells filled with acicular crystals of calcium oxalate. 



The bark has an unpleasant musty odour and a bitter taste. 

 The student should observe 



(a) The cork, which is often spongy, 



(b) The laminated inner portion, 



