183 BARKS. 



(92) Cascarilla Bark, 



The bark of Croton Eluteria, Bennett (N.O. Euphorbiacese). 

 The bark presents the following structure : 



(1) Cork. This tissue varies considerably in extent, and the 

 cells of which it consists exhibit a very remarkable structure. 

 They are strongly thickened and lignified on the outer tangential 

 walls, and the thickening extends over part of the radial walls, 

 the cells thus assuming, in transverse section, a horse-shoe 

 shape ; the inner tangential walls and part of the radial walls 

 contain innumerable minute crystals of calcium oxalate em- 

 bedded in them, and present therefore a granular appearance. 

 In surface view the cells appear polygonal, and uniformly 

 thickened when the outer wall is focussed or thin walled, and 

 filled with a granular substance when the inner wall is 

 focussed. 



(2) Phelloderm, consisting of several rows of radially arranged 

 cells, containing prismatic crystals of calcium oxalate, colouring 

 matter, or droplets of oleo-resin. 



(3) Cortex, usually narrow, and composed of polygonal or 

 rounded cells, containing prismatic or rosette crystals of 

 calcium oxalate, sometimes of very large size, and droplets of 

 oleo-resin. 



(4) Bast Ring, generally of considerable extent, and traversed 

 by numerous, narrow, medullary rays containing a brown sub- 

 stance or prismatic or rosette crystals of calcium oxalate. 

 The bast rays contain numerous secretion cells and also bast 

 fibres. The latter are either isolated or in small groups ; they 

 have very thick walls which, in surface view, often exhibit de- 

 pressions. The secretion cells are rounded or polygonal; in 

 longitudinal section they are rectangular, or bluntly conical, 

 and are often superposed to form a transversely septate tube. 

 They contain either a reddish-brown substance insoluble in 

 alkali, or droplets of oleo-resin. 



The cells of the bast parenchyma contain small grains of starch, 

 or prismatic or rosette crystals of calcium oxalate. In radial 

 sections the cells containing the latter are arranged in vertical 

 rows. 



The diagnostic characters of powdered cascarilla bark are : 



(a) The characteristic secretion cells. 



(b) The bast fibres. 



(c) The cork cells with their remarkable thickening and 



calcium oxalate crystals. 



