BARKS 



253 



the cinnamon barks are found raphides; in cinchona bark, 

 micro-crystals. 



In cocillina, frangula, cascara sagrada, white oak, poplar 

 and Jamaica dogwood barks are found crystal-bearing fibres 

 (Plates 19 and 20). 



When studying barks we must consider the kind, structure, 

 and amount of the periderm; the nature of the phellogen; the 

 nature and amount of the cortical parenchyma; the occurrence, 

 distribution, and amount of stone cells, when present; the 

 occurrence and structure of the bast fibres; the presence or 

 absence of secretion cells; the width, distribution, and structure 

 of the medullary rays. 



