188 XIV. CORK LENTICELS. 



upon potato-tubers. We cut a piece from a sound tuber and 

 preserve it in a moderately moist chamber. The cut surface soon 

 takes a clear brown colour, and after a few weeks we can deter- 

 mine that it is covered by a thin layer of cork. Similarly if a 

 cut or scratch be made upon a young twig of most shrubs, or 

 even upon some leaf-stalks (e.g., Hoy a carnosa), the living cells 

 under those which are wounded will divide tangentially and 

 form a true cork layer. Wound cork may be distinguished as 

 pathological. 1 



1 It seems probable that all cork has, philogenetically, a pathological 

 origin. [ED.] 



