DEFECTS AND DNSODNDKESS. 



39 



respect of great thickness, as it never leads to rottenness. There 

 is no way of recognising it until the tree has been felled and cut 

 up, and it must, of course, be removed before the wood can be 

 employed. 



Article 2. — Unsoundness. 



In a previous Section, under the head of durability, the decay 

 which overtakes felled and, therefore, dead wood through the at- 

 tacks of saprophytic fungi was considered. In the present case 

 the unsoundness occurs in the living tree itself, and, besides being 

 due to the decomposition consequent on the oxidation common to 

 all dead organic matter, is occasioned by parasitic as well as by 

 saprophytic fungi. The ravages of the latter are only local, being 

 confined to the dead tissues, while those of the former may extend 

 through the entire tree. The mycelium of such fungi sends out 

 fine filaments in all directions, which dissolve and absorb every- 

 thing in the shape of food that comes in their way, so that the walls 

 of the tracheides, vessels and cells become attenuated, and from 

 having been closely cemented together and firm and tough and 

 elastic, lose all cohesion and become soft, moist and brittle — in 



Fig. 8 



STokeii dead hranch. 

 (After HartigJ. ' 



