Part IV.] 
PRUNING AND THINNING. 
233 
the water, running down the stem, lodges and 
saturates the parts. This, with the action of 
the oxygen of the air, continues the process of 
decay, which is communicated by contact to the 
heart-wood of the tree: and hollowness of the 
centre is almost always thus caused by rotten 
branches from above, not by rotten roots from 
below. This is the fruitful source of destruction 
to our timber-trees, to the life of which, other¬ 
wise, there is apparently no necessary limit. 
Very little care may avoid this chief cause of 
decay. 
It is not meant to assert that there is no limit 
to the age, or height, or bulk which in a case of 
optimism trees may attain to; but at present 
we know of none. The whole appears to depend 
on circumstances; that is, even if we knew the 
maximum age, or height, or bulk which any par¬ 
ticular sort of tree had ever attained to, it would 
not follow that under more favourable circum¬ 
stances others might not have surpassed it. 
The prejudice against pruning with a saw, or 
the idea of the necessity of afterwards cutting 
the wounds over with a sharp instrument, is 
a vulgar error. The new formation of wood 
and bark over an amputated branch is not 
from the cut wood, which dies, or from the 
Prejudice 
against pruning 
with a saw a 
vulgar error. 
