VIIL] THE CORTEX AND BARK OF TREES. 207 



exposing the cambium and other delicate tissues : it 

 may also serve to show why bark is so various in 

 composition and other characters. But it is also clear 

 that this jacket of coherent bark, bound together by 

 the elastic sheets of cork, must in its turn exert con- 

 siderable pressure as it reacts on the softer, living, 

 succulent parts of the cortex, trapped as they are 

 between the rigid wood cylinder and the bark proper ; 

 and it is easy to convince ourselves that such is the 

 case. By simply cutting a longitudinal slit through 

 the cortex, down to near the cambium, but taking care 

 not to injure the latter, the following results may be 

 obtained. First, the bark gapes, the raw edges of the 

 wound separating and exposing the tissues below ; 

 next, in course of time the raw edges are seen to 

 be healed over with cork produced by the conversion 

 of the outer living cells of the cortex into cork-cells. 

 As time passes, provided no external interference 

 occurs, the now rounded and somewhat swollen cork- 

 covered edges of the wound will be found closing up 

 again ; and sooner or later, depending chiefly on the 

 extent of the wound and the vigour of the tree, the 

 growing lips of the wound will come together and 

 unite completely. 



But examination will show that although such a slit- 

 wound is so easily healed over, it has had an effect on 



