512 BOTANY AND PHARMACOGNOSY. 



this, having a greater or less development of corky layers 

 among more or less obliterated sieve and parenchymatous cells, 

 is known as the outer bark. The term bark is sometimes 

 restricted to this outer layer, but this is more or less confusing 

 and has not been generally adopted. The term bork is frequently 

 applied to the outer corky layers and the dead tissues enclosed by 

 them (Figs. 237, 238). The term periderm is applied to all the 

 tissues produced by the phellogen, the older layers of periderm 

 being included in the bork. 



In a few cases the wood alone is employed in medicine and, 

 like the bark, may be dififerentiated into two layers — the one next 

 to the cambium, in which the ascent of the cell-sap takes place, 

 known as the sap-wood, and another at the center of the trunk or 

 stem, which is usually darker in color and may contain resinous, 

 coloring and other substances, and denominated the heart-wood, 

 the latter being the part usually employed in medicine and the arts. 



The pith being in the nature of a reserve tissue may contain 

 various of the carbohydrates. Sassafras pith furnishes an example _ 

 of this, being used in medicine on account of the mucilage it 

 contains. 



The following artificial classification may be found of assist- 

 ance in the study of the drugs of this class : 



I. Barks. 



I. With periderm. 



A. Yellowish-red to dark brown, 

 a. Fracture short. 



a Aromatic odor and taste. 



Dark brown Cinnamomum Saigonicum 



/3 Without aromatic odor and taste. 

 * Usually in quills. 



Few lenticels Cinchona 



Numerous lenticels Frangula 



** Usually in flattened or transversely curved 

 pieces. 

 Inner surface reddened 



with alkalies Rhamnus Purshiana 



Odor of Valerian. .. .Viburnum Prunifolium 

 Astringent Hamamelidis Cortex 



