VARIOUS TYPES OF CAVITIES 167 



proper treatment is Identical with that just de- 

 scribed for simple basal cavities, with the exception 

 that braces may be required in order to prevent 

 the opening of cracks at the sides of the filling. 



Much more difficult to handle than basal cavi- 

 ties are those in the upper part of the trunk, 

 caused, for the most part, by the wrenching out 

 of a large limb or by some severe injury to the 

 bark. The difficulty of the excavation depends 

 upon the age of the injury. If the decay has 

 worked far up or down the trunk it may be neces- 

 sary greatly to enlarge the original opening. 

 The direction and size of the enlargement should 

 be investigated in advance by sounding the tree, 

 if necessary, with a half-inch bit. Once the exact 

 extent of the decay is known, it is easy to deter- 

 mine the size of the opening necessary for the 

 complete removal of the decay. If the shell of 

 the tree is thin it is best simply to enlarge the ex- 

 isting opening, but if a considerable thickness of 

 sound wood remains, it is well to try to get at the 

 decay from separate openings, above or below the 

 original one, but not less than a foot from it. Or 

 the new opening may be made on another side of 

 the tree if a good opportunity presents itself — a 

 bark wound, for instance, a rotten stub, or a very 

 slow-going area — to make an incision without 

 doing much damage to the tree. The reason for 

 the difference is that the wood between the main 



