192 PRACTICAL TREE REPAIR 



be covered with cotton-batting soaked with an as- 

 phalt dressing. It is likely that a back filling of 

 cinders or sawdust would help to avoid the dis- 

 advantages of tin work, but the writer has never 

 tried that method. 



The nature of the principal strain upon the 

 metal and the way in which it gives way to it, sug- 

 gest the correct limitations to be placed upon the 

 use of metal for covering cavities. It is not so 

 much size which causes the failure of a job of 

 tinning, but rather the amount of variation there 

 is, u;ider stress of the wind, in the size and shape 

 of the opening. A large cavity in a firm trunk is 

 much easier to tin successfully than a smaller cav- 

 ity in a bending and twisting limb. An opening 

 in a tru;ik or branch which swings about much 

 ought not ordinarily to be tinned, as the work 

 is almost certain to be unsatisfactory. It is some- 

 times difficult for a beginner to determine whether 

 a given opening is likely to be variable in size or 

 not. In that case it is best to wait until a windy 

 day comes, when any variation in the size of the 

 opening can be observed. 



Tinning is very well suited to the treatment of 

 small cavities, such as those resulting from the 

 decay of stubs. The treatment of one form of 

 rotten stub, for which tin is especially well 

 adapted, is indicated by the accompanying draw- 

 ings. Metal does very well as a covering for the 



