GENERAL METHODS 121 



enlarged to sound wood an inch or so thick, in 

 order to provide a proper edge for the cavity. 

 If there are old callus lips rolling over the side of 

 the opening of the cavity, and there is rot behind 

 them, they must be cut away. In case new in- 

 cisions are necessary, they are made, when possi- 

 ble, at a place where there is already an injury to 

 the tree, such as a patch of dead bark, or where 

 the wood is thin and the slow growth of the bark 

 indicates that the flow of sap will not be seriously 

 interfered with by an incision. It requires con- 

 siderable experience to enable a man to say in ad- 

 vance just how large an opening will be needed 

 for removing the decayed wood from a cavity, 

 but to dp so often saves much time, for it frequently 

 happens that a man chips a long time at a patch 

 of dead wood which could have been very quickly 

 removed through an opening made later on. 



EXCAVATION 



The openings once fixed on and made, the work 

 of removing the rotten wood begins. At first this 

 is usually easy enough, but it grows harder and 

 harder as the work progresses. All sorts of 

 tricks have to be used In order to get at all 

 of the decay. Sometimes if a gouge won't "bite," 

 a chisel, with its edge toward the wood, will 

 do the work. An extension bit is also very 

 useful in handling " pockets " of rotten wood. 



