THE HANDLING OF THE PLANTS 147 
opening, and filled on the inside with concrete, the brick serving 
the purpose of a retaining wall to hold the concrete in place. 
Concrete used for the main filling is usually 
made in the proportion of one part good 
portland cement, two parts sand, and four 
parts crushed stone, the consistency of the 
mixture being such that it may be poured 
into the cavity and require little or no tamp- 
ing to make the mass solid. (Fig. 160.) 
“Fillings thus made are considered by 
expert tree surgeons to be a permanent pre- 
ventive of decay. The outside of the filling 
is always coated with a thin covering of 
concrete, consisting of one part cement to 
two parts fine sand. Cavities resulting from 
freezing, and which, though large on the in- 
side, show only a long narrow crack on the 
outside, are most easily filled by placing a 
form against the entire length of the opening, 
having a space at the top through which the 
cement may be poured (Fig. 161). Another 
method of retaining the concrete is to re- 
inforce it from the outside by driving rows 
of spikes along the inner surface of either 
side of the cavity and lacing a stout wire 
across the face of the cavity. For best re- 
sults, all fillings must come flush with the 
inner bark when finished. During the first 
year, this growing tissue will spread over the 
outer edge of the filling, thus forming an her- 
metically sealed cavity. In the course of 
time, the outside of small or narrow openings 
should be completely covered with tissue, 
which buries the filling from view. 
161. A wound, made 
by freezing, trimmed 
out and filled with 
cement. 
