1 82 PRACTICAL TREE REPAIR 



little need be said. The excavation is made in 

 substantially the same way that an excavation 

 for a filling is made, though with the important 

 differences that no wood has to be taken out of 



Four sections of the same cavity, showing it before excavation, 

 filled with concrete, covered with zinc and treated by the open 

 system 



it so as to shape the excavation in such a way that 

 it will retain a filling, and that no provision has 

 to be made for a " cambium edge line " from 

 which the callus can grow out over a filling. In- 

 growing calluses need not be removed. If in- 

 cisions through the healthy bark have to be made 

 they should conform in shape and location to the 



