36 TIMBER AND TIMBER TREES. [CHAP. 
decay, owing to the rain and the moisture of the 
atmosphere having entered by the wound, before it 
became hermetically sealed; and, as it generally takes 
a long time, even many years, to completely heal it 
over, it would during all that while be steadily pro- 
ducing decay in the fibres, running from the knot to 
the centre of the tree; the diseased or affected part, 
when opened, being 
often found spread 
to a very great ex- 
tent, and in bad cases 
emitting an unplea- 
sant odour. 
The disease thus 
occasioned first at- 
tacks the alburnum, 
and the fibres imme- 
diately surrounding 
the centre of the 
knot, and then passes 
downwards, following 
wee i the direction of the 
WAS Wy wounded branch to- 
ee Ly wards the pith of the 
XK S= ZY, ZA bole or ae after 
FIG. 13, which it rises with 
. the sap, and is often 
communicated to other parts of the tree, and does very 
great mischief. 
It will sometimes happen that this disease is con- 
centrated, or confined to the root end of the branch, 
producing there what is technically termed a “druxy 
knot.” This defect, if prevented from spreading by 
the otherwise healthy and vigorous state of the tree 
