VARIOUS TYPES OF CAVITIES 175 



The decay substantially cleared away, the cav- 

 ity should be dried by leaving it a few days or 

 by building a fire at the bottom of it. Then the 

 inner walls must be sprayed thoroughly with car- 

 bolineum, a little loose soil being thrown into the 

 bottom of the cavity to catch the drip, which might 

 injure the roots. If the cavity walls are fairly 

 smooth and easily accessible they may now be 

 painted with asphalt in some form. 



The filling should be adapted to circumstances. 

 If there is an opening at the base, the lower part 

 of the chimney can be treated like an ordinary 

 basal cavity, being filled with concrete. Above 

 this point, if there is a fairly large stretch of trunk 

 without openings, it can be filled with packed 

 cinders or gravel, and then a filling of asphalt can 

 be set in at the top of the cavity. To fill the 

 entire trunk of a hollow tree with concrete, to 

 try to " put in a new back-bone," as one firm of 

 tree surgeons has claimed it could, is at once waste- 

 ful and futile. 



In case, for any reason, it is not desirable or 

 feasible to fill the upper part of the chimney with 

 cinders, it can be left open, and the filling of the 

 top opening can be supported on a platform built 

 just below it. Such a platform can be made of 

 boards on bolts run through the trunk, or the plat- 

 form can be made of wires woven back and forth 

 between a dozen nails or staples driven into the 



