92 



BARK OF BIRCH 



[CH. 



of bark, bursting through the superficial periderm and 

 gradually extending so as to cover the whole surface. 

 The older of these small patches begin to flake off before 

 the younger ones, with the result that the stem or branch 

 obtains a peculiarly rough irregularly scaly bark. 



Fig. 43. Birch {Betula alba) : smooth bark (Irv). 



More usually in the Beech, and in the Hornbeam, Hazel, 

 Berheris, &c., the superficial periderms, extending regularly 

 round the stem, graduall}- peel off in broad smooth ring- 

 like lamellre. In the Birch (Fig. 43) this is emphasized 



