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 

 the direction of the 

 wounded branch to- 

 wards 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 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 



FIG. 13. 



