84 THE HEALING OF WOUNDS 



by the saw, and capped over with wood, much 

 as a fruit -jar is capped with a metal cover. 



This Fig. 75 is one of the most important pic- 

 tures in the book, and it is drawn most accurately 

 from a normal and average specimen. It is im- 

 portant because it shows that the end of the old 

 stub has no organic or vital connection with the 

 callus which covers it, but it is merely hermeti- 

 cally sealed in, as a nail or a plug of wood might 

 be.* So far as the vital functions of the tree are 

 concerned, this stub is a foreign and useless body; 

 and no dressing can be expected to hasten the 

 healing -over process. 



The callus ring grows rapidly for a year or two. 

 But hard bark forms on this callus, as it does on 

 other growing wood, and tension or pressure 

 thereby arises and checks the growth. This bark 

 even forms on the under side or lip of the callus. 

 Over the end of the stub in Fig, 75 there is a 

 thin layer of bark. We have already found that 

 slitting the bark upon a trunk relieves the pres- 

 sure and allows of extra -rapid growth at that 

 point. Suppose, then, that if the callus ceases 

 to grow, the operator make a circular cut with a 

 knife -point on the inner edge of the callus -roll ! 



In surface wounds which expose the wood, the 

 callus also forms from the cambium and covers 

 the denuded area. If the injury does not extend 



*If the reader desires to know how a graft-stub is buried, he may con- 

 sult Fig. 133 in the last edition of "The Nursery-Book." 



