OAK 283 



possesses a smooth, glossy, silvery cork ; such bark is to be preferred 

 and should alone be used medicinally. 



Description. Oak bark usually occurs in channelled pieces 10 

 to 20 cm. in length and 2 to 3 cm. in breadth. The outer layer is 

 a thin, smooth, shining, silvery-grey, firmly adherent cork, which 

 in young barks is marked with darker transverse lenticels and' in 

 older barks is frequently longitudinally fissured and bears darker 

 spots and patches ; beneath the cork is a reddish brown cortex. 



FIG. 141. Oak bark. A, outer surface, showing the smooth, 

 glossy cork and transverse lenticels. B, inner surface. 

 Natural size. 



The inner surface is strongly striated longitudinally and fibrous, 

 and varies in colour from yellowish to reddish brown. 



The bark breaks with a short fracture in the outer part (cork and 

 cortex), but is coarsely fibrous in the inner part (bast). Under a 

 lens the section exhibits a thin cork, a narrow yellowish cortex, 

 occupying about one fourth of the total width, separated by a 

 pale line (sclerenchymatous cells) from the reddish brown bast, which 

 is chequered by tangentially arranged groups of bast fibres. Touched 

 with dilute solution of ferric chloride the section assumes a black 

 colour. 



