Part IV.] 
PRUNING AND THINNING. 
225 
the dead wood which is inclosed forms an impe¬ 
diment to the course of the sap, and a conse¬ 
quent distortion of the grain, as much as if a 
bolt of iron were passed into the tree. 
Now, the great objection to a cross-grain or 
to an united knot is, that it prevents the timber 
from cleaving and working well, as the carpenters 
say: but it does not weaken the timber, or 
render it more liable to break; but at every 
disunited knot the timber is already broken , be¬ 
sides the cross-grain. 
De Candolle remarks that, as the girthing of 
the branch is at first extremely small, but in¬ 
creases annually, each year the stem incloses a 
larger circumference; and that part of the 
branch which is inclosed is in the form of a 
cone, its base at the bark, and diminishing in¬ 
wardly towards the pith. The outer part of the 
branch is in the form of a cone, its base at the 
bark, diminishing outwardly. But no such in¬ 
ternal cone exists except in appearance, that is, 
in colour , when a branch has died while the tree 
was alive : and doubtless De Candolle has been 
deceived by the appearance of knots formed by 
branches which died and dried before the tree 
was cut. When a branch dies while the tree is 
alive, it will indeed dry in and change colour in 
Q 
