378 



Diseases of Economic Plants 



be undercut so that the fiUing will be held firmly in place, 

 but, lest they dry out, should not be less than three- 

 quarters of an inch thick, better an inch and a half. If 

 there is but little undercutting, nails may be driven into 

 the interior to hold the filling. The final cutting around 

 the cambium should be made with a sharp knife and imme- 

 diately followed by a coating of shellac covering the edges 

 of the cambium, bark, and sapwood. In cavities more than 

 two feet long, it may be necessary to reinforce the remaining 

 wood by bolts placed every 18 to 24 inches at appropriate 

 angles. After excision is completed, the entire inner surface 



Fig. 199. — Least objectionable method of an- 

 choring guy wires to trees. After Stone. 



should be disinfected with creosote or carbolineum, and over 

 this a heavy coating of tar or hot asphalt applied. 



The cavity may then be filled, using Portland cement and 

 sand (1 to 3) well tamped in, the cement being put in to form 

 blocks about 12 inches high and separated by tarred roofing 

 paper. The face of the cement should be trimmed back to 

 the level of the cambium. Instead of filling the cavity with 

 cement, a mixture of dry sawdust and asphaltum, 3 or 4 

 parts to 1, may be used, with the advantage of greater 

 elasticity to meet the winds. Or the cavity may be left un- 

 filled and simply covered with a concrete layer with ap- 

 parently equal advantages and much saving of cement. 

 Metal coverings of tin or zinc are sometimes used, but in 

 general are not so desirable. Shallow cavities are merely 



