176 MASS. EXPERIMENT STATION BULLETIN 170. 



or healing tissue. It is therefore essential that the shape of the cavity 



opening conform to the path of the translocated plastic substances of 

 the tree. These are confined to the phloem, or 

 inner bark. The sides of the cavity opening 

 should, in a general way, conform; and the less 

 the irregularity of the edges of the opening the 

 better. 



If the cavity is above the surface of the ground 

 the apex and base of the opening should never be 

 truncated or flattened, but should be apiculate or 

 pointed. There is no particular objection, how- 

 ever, to having the opening of the cavity per- 

 fectly square or rectangular if the bark is re- 

 moved above and below the opening and brought 

 to a pointed or rounded termination. (See Fig. 

 49.) This allows the healing tissue to form reg- 

 ularly and uniformly over the outside of the 

 cavity. Tliis also holds true in the treatment of 

 scars and abrasions on trees. After removing 

 the bark the wood should be scraped and treated 

 as with any wound. 



Concrete Fillings. — Concrete has been used 

 more largely than any other substance for fill- 

 ing cavities in trees, but its physical properties 

 are so unlike those of wood that it has never been 

 regarded by competent authorities as a suitable 

 material for work of tliis nature. By some workers 



its use has only been tolerated until something better could be substituted. 

 Some of the numerous objections to be raised against filling cavities 



with cement are as follows : — 



Fig. 43. — Demonstrating 

 the object of treating 

 cavities. Upper figure 

 shows cavity of long 

 standing, with callus 

 curved in, which, if it 

 had been treated, 

 would be as repre- 

 sented below. 



Fig. 44. — Cross-section of filled cavity showing one 

 method of treatment. B, bark; Y, sapwood; M, 

 medullary rays; H.heartwood; A, annual rings, 

 G, grouting; S, cement surface covering; W, wire 

 re-enforcement; E, elastic cement. Inferior to the 

 (irv cement methods now used. 



