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. 
