222 SHADE-TREES IN TOWNS AND CITIES 



employed for the reenforcement of the tree or the retention 

 of the filling. The cavity is finished in a way that it will 

 retain the filling. In the case of small ones it is sufficient if 

 the interiors are made larger than the openings. Shallow 

 cavities and those of considerable size are treated in another 



FIG. 33. A transverse section of a tree showing the precautions to be 

 taken when preparing a cavity for filling. The rolls of tissue must be 

 cut away to the points A A, and all decayed wood removed. The 

 filling must follow the natural contour of the tree, B C B, and stop at 

 the points B B, depressed a distance equal to the thickness of the bark. 



way. A deep channel is cut just inside of the opening, all 

 around the periphery, and this helps to retain the cement. 

 Before filling, the cavity is sterilized by washing with an 

 antiseptic solution of copper sulfate, one pound to fifteen 

 gallons of water, and then covered with molten coal-tar. In 

 order to secure a better adhesion of the cement to the walls 

 of the cavity, the hole is filled before the tar hardens. To 



