THE STEM. 93 



the outside. The stelar cambium arises between the wood 

 and the bast strands of each pair, and extends across the 

 pith ray? which intervene, thus forming a complete zone 

 nearly concentric with the surface of the stem (figs. 78, 81, 



Fig. 83. — Part of a transverse section of the bark of cinchona, c, layers of cork formed 

 by a transient cork cambium, j, thin-walled tissues, with occasional stone cells. The 

 sheets of cork cells are lines of weakness along which the Hakes of bark split off. 

 Magnified 665 diam.— After Warnecke. 



84, A). On the inside of the cambium there arises, opposite 

 the primary wood, secondary wood. Outside the cambium, 

 opposite the primary bast, there arises secondary bast. Each 

 strand is thus increased in its radial thickness (fig. 8i). 



115. Pith rays, — The cambium in the pith between the 

 bundles either produces pith tissue (B, fig. 84), or it forms 

 secondary wood and bast corresponding to that produced 

 between the adjacent bundles. In the latter case, therefore, 

 a complete zone or ring of secondary wood and bast is 



