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 producing decay in the fibres, running from the knot to the centre of the tree; the diseased or affected part,
FIG. 13.
when opened, being often found spread to a very great extent, and in bad cases emitting an unpleasant odour.
The disease thus occasioned first attacks the alburnum, and the fibres immediately surrounding the centre of the knot, and then passes downwards, following the direction of the wounded branch towards the pith of the bole or stem, after 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 concentrated, 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
