Bark 



49 



tective coat to the exterior of the stem. After a short time the 

 cells generally become dead, and very often peel off under the 

 expanding influence of the growth of the stem. 



Fig. 71. — Longitudinal tangential sociion of stem of Ailanthiis, showing secondary 

 xylem of fibro-vascular bundles : g; g, wood vessels ; p, wood parenchyma ; t, Ij, 

 wood prosenchyma, of two varieties ; t, trachei'des, with pitted and spiral mark- 

 ings, and Iff hbriform or bast-like wood fibres ; st^ medullary rays cut across. 

 (After Sachs.) 



This, as is seen in the Elm or Cork Oak, gives a rugged 

 appearance to the bark. In other cases, as in the Beechj 



E 



