TREE SURGERY 353 



wood beyond the limits of evident decay and discoloration. A 

 layer of apparently healthy wood outside the discolored area 

 must be removed from all sides of the cavity to make sure that 

 all of the mycelium is eradicated. 



The size of the opening of the cavity should be no greater than 

 is absolutely necessary, as healthy sapwood and bark must be 

 conserved. The form of the opening will depend on conditions, 

 except that it must be pointed below and above, as in the case 

 of canker excision, to insure rapid healing at these places. The 

 edges of the cavity must be clean cut and should be shaped with 

 a chisel or gouge. The bark may be finally shaped with a strong 

 knife. Shellac should be applied to the bark and sapwood as 

 this is done. 



For cavity work, gouges of various sizes, chisels, a mallet and 

 a heavy knife are needed. In opening a diseased area, it is 

 often necessary to cut away healthy sapwood and bark in order 

 to get at the decayed wood with the gouge. Often the diseased 

 wood must be followed for some distance above and below the 

 original opening. Instead of making other small holes in' the 

 bark and sapwood, a narrow continuous opening is much better. 

 The bridges of healthy bark and sapwood left, when holes are 

 made; are bad practice for two reasons : the decayed wood is 

 not as effectively removed and the bridges are likely to die and 

 may be the source of future diflficulty. 



Cavity Treatments 



At this point it must be decided whether or not the cavity is 

 to be filled. Cavities may be treated in one of three ways : 

 (1) left open; (2) closed by sheet metal conforming to the 

 position of the original bark; and (3) filled with solid sub- 

 stances. The last method is the most commonly practiced and 

 is the most expensive and, in the main, least scientific. 



If the cavity is not to be filled, no further shaping is neces- 

 2a 



