IX.] HEALING OF WOUNDS BY OCCLUSION. 217 



provided the wound is not too large, and the tree is 

 full of vigour, the margins of the callus will meet near 

 the middle, and what was the exposed cut surface 

 of the branch will be buried beneath layers of new 



Fig. 31. — The same piece of stem six years later still : the surface of the cut branch 

 has now been covered in for some time, and only a boss-like projection marks 

 where the previous cut surface was. This projection is protected by cork layers, 

 like ordinary outer cortex, the old outer cortex cracking more and more as the 

 stem expands. 



wood and cortex, between which lies the cambium 

 now once more continuous over the whole trunk of the 

 tree (Figs. 31 and 32). 



It is not here to the purpose to enter into the very 



