232 
PRUNING AND THINNING. 
[Part IV. 
side-branches in bulk, and for finally taking them 
off while small. 
On cutting across the part of a branch which 
I had rung, I found that in the course of twelve 
years the outside wood . had died, and dried in 
only to the thickness of paper. From this I 
imagined that the case would be the same with 
the ends of amputated branches. I think it, 
however, probable that the reason why so slight 
a surface of the rung branch died and dried was, 
that the whole of the internal wood remained 
the conduit of the upward sap. In the case of 
amputated branches, the internal wood would 
cease to be a conduit of sap, and the whole pro¬ 
bably dies and dries in as far as the cross-grain. 
This would occasion a knot to that extent; but 
it would be a knot united annually growth for 
growth with the stem-wood, and not like the 
detached knots which are formed by the inclos¬ 
ing in the stem of branches which have died. 
The healing takes place over a dead branch 
which is cut off in the same manner as over a 
living one. But if a dead branch is left till it 
becomes rotten where it joins the stem, as there 
is no firm surface for the deposit of new wood, 
the new growth curls round upon itself, and a 
hole remains in the stem of the tree. In this 
