250 



BARKS 



In pieces of medium thickness the outer layer (cork) is usually 

 of a dull grey colour, but sometimes it is so dark as to be nearly black ; 

 it is interrupted by reddish warts or circular spots that eventually 

 fuse together into longitudinal bands. Older and therefore thicker 

 barks are rugged, and have a more uniform reddish brown colour. 

 They often exhibit conchoidal depressions of considerable size (1 to 2 

 cm. long), the whole surface, elevations as well as depressions, being 

 ruggedly ridged. In these barks most of the primary cortex has 



FIG. 127. Sassy bark. A, portion of bark of medium thickness, showing 

 fissured surface ; B, portion of very thick bark showing rugged surface, 

 with depressions produced by exfoliation of the outer portion. 



been exfoliated by the formation of cork.- Very young bark is com- 

 paratively smooth and dark in colour ; it bears occasional small 

 reddish warts and exhibits longitudinal reddish bands. 



The inner surface exhibits shallow longitudinal striations or eleva- 

 tions, and is of a dark reddish brown or, more commonly, dull black 

 colour. 



The bark is extremely hard, and breaks with a very short granular 

 fracture. The transverse section examined under the lens is most 

 characteristic. The cork appears as a narrow brownish line ; the 

 cortex is narrow and darker in colour, and separated from the bast 

 by a pale complete or interrupted line of sclerenchymatous cells. 

 The bast, which constitutes the major part of the larger and thicker 



