i6 4 TREES AS GOOD CITIZENS 



be repeated in two or three inch layers until the filling is 

 complete, and the tamping should always be directed 

 toward the back of the cavity rather than toward the 

 bottom. The filling should stop at a point even with the 

 surface of the wood. To allow the cement to project 

 outside the wood, so that it is flush with the outer surface 

 of the bark, will delay the purpose for which the operation 

 was performed, as such projection will prevent new tissue 

 from covering the opening without first lifting the edge of 

 the old bark and growing up over the cement. If the filling 

 is flush with the surface of the wood and the cambium has 

 not been injured, a healing callous will promptly grow over 

 the edges, and if the wound is small this new growth may 

 eventually cover the entire surface. In overlapping the 

 edges of the cement, this new tissue completely seals the 

 cavity and usually keeps out moisture in small cavities. 



After the cement has dried, its surface should be coated 

 with coal tar, to prevent unnecessary absorption of water. 



Often creosoted wood blocks, sawdust and tar are used 

 instead of cement and have some advantages, especially 

 less weight, without marked disadvantages. 



If the cavity is long and deep, leaving little more than 

 a shell of a trunk, the tree should be removed unless there 

 is some very special reason for trying to prolong its life. 

 If it is determined to fill the cavity, the tree should be 

 braced and guyed and then the cavity should be reinforced 

 by means of one or more bolts. A cavity less than two 

 feet long usually requires no such reinforcement, but in 

 those of greater length a bolt every two feet is desirable. 

 The bolting is done in fashion similar to the process of 

 bolting split crotches. The bolt should be half an inch 

 thick, or even larger for trunks of considerable size, and 

 must fit snugly into the hole bored for its reception. 

 It should be placed where the nature of the cavity indi- 



