20 



PRACTICAL TREE REPAIR 



lower edge is in a sort of back-water, where it 

 gets but little nourishment. In some cases, as 

 often on the oak, these differences are not so dis- 

 tinct. 



The effect of the tendency of the sap to flow 

 in continuous vertical channels is well illustrated 



by the results of the 

 way sap has of flowing 

 by an irregular bark 

 wound. Suppose that a 

 patch of bark of the 

 shape indicated in the 

 diagram is torn from a 

 trunk, and that the ex- 

 posed cambium dies. 

 What will happen is 

 obvious enough. The 

 tongue B (see draw- 

 ing) , being entirely 

 isolated from the flow 

 of sap (which, it must be remembered, is normally 

 downward) , will soon die back to the dotted line. 

 The tongue A will probably die, but that is not so 

 certain, for projections from the upper edge of a 

 wound stand a better chance of getting nourish- 

 ment. Calluses will of course be formed at the 

 sides of the wound. 



On the basis of these observations, we can 

 formulate a general rule for the shape of incisions. 



An irregular bark wound 



