PRACTICAL TREE SURGERY 387 



diseased wood. This often extends some distance above and below 

 the visible discolored area. 



The most important feature of this stage of the work is to re- 

 move all the diseased and insect-eaten wood (Fig. 305 B, C). This 

 excavating must continue on all sides of the cavity until sound 

 uninfected wood is reached. All discolored or water-soaked 

 heartwood should be removed, as this is the region in which the rot- 

 producing fungus is most active. In decayed areas of many years' 

 standing there may be only a thin shell of uninfected wood around 

 the cavity (Fig. 301 F), in which case there is danger of the tree 

 being broken by storms unless braced or guyed. 



294. Drainage. The bottom and all other parts of the cavity 

 should be so shaped that if water were thrown into the cavity it 

 would promptly run out and none remain in any hollow. This fea- 

 ture is commonly called "drainage." It is bad practice to have a deep 

 water pocket at the bottom of a cavity with drainage through an 

 auger hole bored from the exterior. An open hole of this sort often 

 becomes a favorable lodging place for insects or fungous spores. 



295. Undercutting. Another important point in shaping a cavity 

 is to have the sides undercut if possible, so as to hold the filling 

 firmly in place. Care must be taken, 



however, not to have the wood at the 



edges of the opening very thin, as this 



promotes the drying out of the bark and 



sap wood at these points. Ordinarily the 



edges should be at least 34 of an inch 



thick, and \ l /> would be better (Figs. 301 D, 



306 A). Inrolled bark at the edges of an 



opening should be cut back in nearly 



parallel radial planes, as a rule, to a point 



which will permit the surface of the 



completed cement filling to conform with 



and continue across the cavity the general 



contour of the woody part of the trunk J PLACED BOLT 



(Fig. 306 A) . If it is not possible to under- HEAD 



cut sufficiently to hold the filling firmly in 



place, the alternative method described under "Nailing' (297) may 



be adopted (Fig. 306 B). 



Great care must be exercised in working around the cambium, 

 and all cutting tools must be kept very sharp. The final cutting along 

 the edges of the bark and the sap wood can usually best be made 

 with a very sharp knife. This cutting must be followed immediately 

 by a coating of shellac, which should cover the edges of both bark 

 and sap wood. 



296. Bolting. Before cementing a long cavity it is advisable to 

 place through it one or more bolts, so as to hold the wood and the 

 cement more firmly in place. A cavity 2 feet or less in length will 

 not usually require a bolt, but long cavities, as a general rule, should 



