SECTION VII 



BARKS 



The term ' bark ' is commonly employed by pharmacognosists to 

 denote all the tissues of the stem and root of trees and shrubs exterior 

 to the cambium. It comprises, therefore, botanically, such tegumen- 

 tary tissue as may have been formed, primary and secondary cortex, 

 together with primary and secondary bast. 



In examining a bark attention should first be directed to the shape 

 of the pieces in which it occurs. 



Barks are said to be in fiat pieces when they are quite flat ; in 

 curved pieces when they present a curved but not deeply concave 

 transverse section ; in recurved pieces when the concave surface is 

 the outer portion of the bark ; in channelled pieces when the transverse 

 section is deeply concave. Should it be so deeply concave that the 

 edges nearly or quite overlap, a quill is produced, and should both 

 edges be inrolled a double quill is formed. Single or double quills 

 packed inside one another form compound quills. 



Next the physical characters should be noted, such as colour 

 odour, taste, nature of the outer and inner surface, &c. 



The appearance of the edges when a piece is broken (' fracture ' 

 of a bark) often affords useful information ; the fracture may be 

 short, granular, splintery, or fibrous terms which sufficiently explain 

 themselves. 



As the bark of any particular tree may be, and frequently is, 

 collected from axes varying in size from a twig to a large trunk, the 

 drug thus produced will exhibit not only corresponding variations in 

 size, but also considerable variation in external appearance caused by 

 the changes in the tegumentary tissue due to the growth of the axis. 

 The internal structure, however, retains its important characteristics 

 unchanged, and the student should therefore carefully examine a 

 smooth transverse section which he will find an excellent and often 

 indispensable guide to the identification of a bark. Before passing 

 to this part of the work he should study the anatomy of the bark in 

 his text-book of botany ; the following brief notes may, however, be 

 useful. 



