Street Trees. 



333 



cement, two parts sand, and four parts crushed stone, the consistency 

 of the mixture being such that it may be poured into the cavity and 

 require httle or no tamping to make the mass soHd. FilHngs thus 

 made are considered by expert tree surgeons to be a permanent pre- 

 ventive of decay. The 

 outside of the filhng 

 is always coated with 

 a thin covering of con- 

 crete, consisting of one 

 part cement to two 

 parts fine sand. Cavi- 

 ties resulting from 

 freezing, and which, 

 though large on the 

 inside, show only a 

 long narrow crack on 

 the outside, are most 

 easily filled by placing 

 a form against the 

 entire length of the 

 opening, having a 

 space at the top 

 through which the ce- 

 ment may be poured. 

 Another method of 

 retaining the concrete 

 is to reinforce it from 

 the outside by driving 

 rows of spikes along 

 the inner surface of 

 either side of the cav- 

 ity and lacing a stout 

 wire across the face of 

 the cavity. For best 

 results, all fillings m.ust 



come flush with the inner bark when finished. During the first 

 year, this growing tissue will spread over the outer edge of the filling, 

 thus forming an hermetically sealed cavity. In the course of time, 

 as the cambium continues to expand, the outside of small or narrow 

 openings should be completely covered with living tissue, which buries 

 the filling from view. 



Fig. 254. — A large tree requiring immediate attention, if 

 the specimen is to be preserved. 



