THE EPIDERMIS AND PERIDERM 85 



The presence or absence of cork or epidermal tissue in pow- 

 ders must always be noted. The presence of cork enables one to 

 distinguish Spanish from Russian licorice. In like manner, the 

 presence of epidermis enables one to distinguish the pharma- 

 copceial from the unofficial peeled calamus. The absence of 

 epidermis in Jamaica ginger is one of the means by which this 

 variety is distinguished from the other varieties of ginger, etc. 



In canella alba the periderm is replaced by stone cell-cork. 

 That is, the cells forming the periderm are of a typical cork 

 shape, but the walls are lignified, unequally thickened, and 

 the inner or thicker walls are strongly porous, and the walls 

 are of a yellowish color. Stone cell-cork forms the periderm 

 of clove bark also, but the cells are narrower and longer, and 

 the inner wall is not so thick or porous as is the case in canella 

 alba bark. 



STONE CELL PERIDERM 



In canella alba (Plate 17, Fig. B) cork periderm is frequently 

 replaced by stone cells, particularly in the older barks. These 

 stone cells form the periderm because they replace the cork 

 periderm, which fissures and scales off as the root increases 

 in diameter. 



The side and end walls of cork cells are of nearly uniform 

 diameter. Exceptions occur, but they are not common. In 

 buchu stem (Plate loi, Fig. 3), the cork cells have thick outer 

 walls, but thin sides and inner walls. The cell cavity contains 

 reddish-brown deposits of tannin. 



PARENCHYMA AND STONE CELL PERIDERM 



As the trees and shrubs increase in diameter, cracks or fis- 

 sures occur in the periderm, or corky layer. In such cases the 

 phellogen cells divide and redivide in such manner as to cut 

 off a portion of the parenchyma cells, stone cells, and fibres of 

 the cortex which is inside of and below the fissure. All the 

 parenchyma cells, etc., exterior to the newly formed cork cells 

 soon lose their living-cell contents, since their food-supply is 

 cut off by the impervious walls of the cork cells. In time they 

 are forced outward by the developing cork cells until they 



