190 BARKS. 



(93) Cassia Bark. 



The bark of Cinnamomum Cassia, Blume. (N.O. Laurinese). 

 The bark presents the following structure : 



(1) Cork, in which layers of thin-walled, tabular cells alter- 

 nate with layers of cells with thickened, brown walls. 



(2) Cortex, which is moderately wide and characterised by the 

 abundance of sclerenchymatous cells contained in it. Some of 

 these cells have very thick walls with branching pits ; others 

 have comparatively large cavities and walls that exhibit a more 

 or less conspicuous one-sided thickening. They occur either 

 isolated or in small groups in the primary cortex, and also form 

 a sclerenchymatous ring, which is interrupted at intervals by 

 small groups of pa^enchymatous cells, and bears on the outer 

 margin scattered bundles of pericyclic fibres. 



(3) Bast Ring, constituting the greater part of the bark. It is 

 traversed by medullary rays two cells wide, and contains 

 numerous secretion cells as well as bast-fibres and sclerenchy- 

 matous cells. The secretion cells are mostly larger than the 

 cells of the bast parenchyma, and are axially elongated ; they 

 may contain either mucilage or volatile oil, or a mixture of 

 both. The bast fibres are either isolated, or occur in groups of 

 two or three ; they are larger but less numerous than those of 

 cinnamon bark. The sclerenchymatous cells are also either 

 isolated or in small groups. The cells of the bast parenchyma 

 contain starch grains which are considerably larger than 

 those of cinnamon bark. Many cells, especially those of the 

 medullary rays, contain numerous minute prismatic crystals of 

 calcium oxalate. The sieve-tubes are narrow, and have small, 

 transverse sieve-plates. 



The diagnostic characters of cassia bark are : 



(a) The cork, some of the cells of which are thick walled. 



(b) The isolated bast fibres. 



(c) The sclerenchymatous cells, many of which are more 



strongly thickened on one side than on the other. 



(d) The secretion cells, containing oil or mucilage ' 



(e) Th<t minute prismatic crystals of calcium oxalate. 



Typical specimens of cassia bark may be distinguished from 

 typical specimens of cinnamon bark by the presence of cork, by 

 the larger, thicker, bast fibres, and by the larger starch-grains, 

 but the lower grades of cinnamon bark are often difficult to 

 distinguish from cassia. 



