f 



73 



200. In the bark itself, an anuular layer of growth is also formed 

 next to the wood, and in some cases wo may count the distinct lay- 

 ers i 1 'growth of recent years; but iu otlicr cases they become a 

 homogeneous mass, as seen by the naked eye, and the outer layers 

 an; gradually cast off. Iu some trees, like the birch and the cherry, 

 the outer layers consist of strong fibers, running hori/oiitally uround 

 the trunk and branches. These may exfoliate in loose shreds. This 

 tendency to exfoliation is shown in the plane tree, where the outer 

 bark falls oil' in hard masses, leaving a livsh surface, at first white, 

 but becoming greenish, and in the Scotch pine, (Pimu tyhatrid), in 

 which the outer bark peels ojf iu thin flakes from the upper part of 







gt 



111 



ill 



01. Longitudinal Portion of the Bnrk 

 (.!' ihe Linden: showing the minute 

 interlocking libers of tin- l>iist-t>im- 

 illes. crossing the longitudinal 

 lit ers.(l) 



62. Transverse Seetion of the Bnrk of the 

 Linden: showing the outer bark, h; 

 the green cellular layer, ft; the hast- 

 layer. t>; ninl the edge of contact with 

 the wood.f/r; with the medullary rnys 

 of the liurk, m, m, in. m, m, extend- 

 ing into the green cellular layer. (1) 



the trunk, and from the branches, leaving a smooth and fresh green 

 surface. 



LMH. When the bark and wood of a tree are cut or wounded by 

 accident, as by the marking-hammer of the forester, or the ax of a 



1 From Rossmassler. 



