VARIOUS TYPES OF CAVITIES 165 



away several inches so as to give a chance to in- 

 spect and treat the remaining roots. 



All decay having been removed, but little more 

 cutting is usually required. No great effort should 

 be made below the surface of the soil, as is often 

 necessary in handling openings in the upper trunk 

 to arrange the edges of the cavity in such a way 

 that the calluses will heal over the filling. It is 

 possible to do much in that way only at the foot 

 of the filling, in connecting up the filling with the 

 large roots usually found on each side of a basal 

 cavity. The patches of bark which have to be 

 removed from the roots in this operation are of 

 slight consequence, on account of the fact that 

 they are aside from the main flow of sap. 



Basal cavities of the type we have been dis- 

 cussing do not often need any bracing. The cen- 

 ter is so much larger than the mouth that bracing 

 is not frequently required to retain the filling in 

 place, and it is not possible to add much strength 

 to a tree by putting in braces so low down in the 

 trunk. 



As a dressing for the inside of the cavity, tar 

 will do very well, for the good drainage removes 

 the principal reason for a heavier covering of the 

 wood. 



The work of filling the excavation is fairly sim- 

 ple. If there are any pockets, such as might be 

 caused by removing the decay from a root, they 



