72 TECHNICAL PKOPERTIES OF WOOD. 



roots, or through wounds in branches, &c. ; or may be owing to 

 want of oxygen in the soil, or to moisture and air from the 

 atmosphere penetrating through external wounds, in which 

 fungi eventually grow. Whenever wood is attacked by parasitic 

 fungi the evil spreads rapidly, the wood losing its coherence 

 owing to the growth of the mycelia and the decomposition of the 

 cell-walls, and assuming various colours* and appearances, 

 according to the kind of fungus which attacks it. 



Red-rot is caused in the spruce and silver-fir by Tramctes 

 radiciperda, Pidyporns vaporavias and P. mollis ; in the larch, 

 oak, poplars and willows, by P. Hulphurem, and in the oak also 

 by TJidcpJiora j^erdix. 



White-rot is caused in the silver-fir by Pulyporus fidvus and 

 Agaricus melleus; in the spruce by P. horealis and A. melleus : 

 in the Scotch pine, Weymouth-pine, and larch, by A. melleus ; 

 in the oak by P. if/niariiis, P. drj/adcits, I{i/d)ini)i diversidcns, 

 and Stcreum Jnrsutam ; in the beech by Ili/dniun diversidcns. 



Root-rot is commonest with the Scotch pine, and rarer in the 

 case of the spruce and other species, and causes a kind of white-rot. 



All decay due to wounds first causes a dark brown discolora- 

 tion of the wood (red-rot), which may eventually turn into white- 

 rot; the products of the decomposition are often carried far, 

 both upwards and downwards, into the stem by the sap. Such 

 decaying wounds continue to increase only as long as the wound 

 is open and rain-water gains admission into the tree. The part 

 of the tree infected, the amount of infection, and its influence on 

 the future utility of the wood, are naturally very variable. 



(b) Decay of the Separate Parts of a Tree. 



A distinction can be made between decay within the tree itself 

 and external decay. 



i. Intcnicd 1 frcaij. 



The interior of a tree may be decayed without there being 



any easily apparent external signs of the damage. Such decay 



commences either at the roots or through the branches or wounds 



in the bark, and penetrates to the interior of the tree. It 



* [These are very clearly shown in coloured ytlates given hy Hartig in his 



Bauiakrankhciteny which arc not, however, reproduced in tiie Engli&ii transla- 

 tion of that work. — Ti:.] 



