248 
PRUNING AND THINNING. 
[Part IV- 
measured, though probably the pollards never 
girthed large as sound trees. Even when the 
circle is broken, and they stand like detached 
strips of bark, the new deposit of wood and bark 
takes place on their outside, while their inside 
is sloughing, or rotting off, and these detached 
strips gradually and annually progress outwards 
from where the centre of the tree was. 
When old pollards are cut over, they throw 
out new branches most vigorously, which mili¬ 
tates against the theory, that all new branches 
are from original latent buds, and from the 
central pith; since old pollards may be found 
not only destitute of central pith, but the oldest 
part of whose stem-wood is possibly not ten 
years of age. So that the casuist might raise the 
question whether these our supposed oldest trees 
are not actually among our youngest; as the 
identity of the ship Argo was disputed when, from 
constant gradual repair in the temple where it 
was preserved, every part of the old ship had 
disappeared and had been replaced. Nay, since 
whilst a pollard is becoming hollow the internal 
decay surpasses the external growth, it may be 
said to become younger by age; and when 
decay and growth balance each other, that age, 
or the addition of years, makes it no older. 
