98 BARK OF BEECH [CH. 



due to betulin, is here effective as also in the case of 

 Eucalyptus, which is also a sun-exposed genus. 



Trees with thin bark, such as Beech (Fig. 47), Spruce, 

 Hornbeam, &c., are impatient of exposure unless in clumps 



Fig. 47. Beech (Fagus sylvatica) : thin periderm clothing the trunk (Irv). 



where some mutual shading is afforded, and it is noticeable 

 that just such shade-enduring trees suffer most if suddenly 

 exposed, by fellings, to the solar rays, especially those from 

 the south-west impinging on the exposed trunks are apt 

 to produce sun scorching. 



