JL86 BARKS. 



(91) Cascara Sagrada. 



The bark of Rhamnus purshiana, D.C. (N.O. Rhamnese). 



The bark presents the following structure: 



(1) Corky composed of several layers of small, flattened cells 

 with brown contents ; in surface view these cells are polygonal. 



(2) Cortex, the cells of which are tangentially elongated. 

 Near the cork these cells are collenchymatous in character, 

 forming a more or less continuous band of thickened cells. This 

 tissue contains numerous large groups of sclerenchymatous 

 cells, the individual cells of which are of irregular shape, and 

 have very thick, striated, pitted wails. The parenchymatous 

 cells abutting on these groups of sclerenchyma often contain 

 prismatic crystals of calcium oxalate, whilst in the remainder 

 of the cortical parenchyma numerous rosettes of calcium 

 oxalate are to be found 



(3) Bast Ring. This tissue is traversed by medullary rays 

 from one to four cells wide. It contains numerous, narrow, 

 tangentially elongated groups of thick-walled bast fibres upon 

 which parenchymatous cells containing prismatic crystals of 

 calcium oxalate abut. These latter cells are arranged in 

 long vertical rows, and their contents are very conspicuous in 

 longitudinal sections. The sieve-tubes are mostly wide, and- 

 bear large sieve-plates on oblique walls ; they can by suitable 

 treatment be detected in the powder. The bast ring contains in 

 addition smaller groups of sclerenchymatous cells and- 

 numerous rosettes of calcium oxalate. 



The diagnostic characters of powdered cascara sagrada 

 are : 



(a) The conspicuous bast fibres accompanied by calcium' 



oxalate crystals. 



(b) The groups of sclerenchymatous cells, or fragments of 



such groups. 



(c) The small cork cells with reddish-brown contents. 



(d) The large sieve-tubes with oblique plates. 



(e) The purplish colour produced wlien the powder is- 



treated with a caustic alkali. 



