BARKS. 181 



SECTION VII. 



POWDERED BARKS. 



The cells and tissues contained in barks exhibit, as a rule, 

 much less variety than those contained in leaves, flowers, seeds, 

 or fruits, and, consequently, in powdered barks there are fewer 

 diagnostic characters available for the purpose of dis- 

 tinguishing such powders from one another or from other 

 powdered drugs. In studying this section, therefore, the 

 student must pay particular attention to the details exhibited 

 by the various elements present. 



It is desirable, first of all, to point out the difference that 

 exists in the definition of the term " bark." Modern botanists 

 apply the term bark to those tissues of the stem that are cut 

 off by successive phellogens, and consequently become dried up, 

 forming a layer of varying thickness, composition, and character 

 on the outside of many stems. Pharmacognosists, on the other 

 hand, understand by bark all the tissues of the stem exterior to 

 the cambium, and include in the term, therefore, bast, pericycle, 

 endodermis, cortex and epidermis, together with any tissues 

 that may be formed in these. Should secondary growth have 

 taken place, then the tissues thus produced, in so far as they are 

 exterior to the cambium, are included in the term bark. Older 

 barks will therefore contain secondary bast in addition to 

 primary, secondary cortex in addition to or in place of primary, 

 cork in place of epidermis, and possibly also outer bark (the 

 " bark " of botanists). 



