HEART-ROT CAUSED BY OTHER FUNGI 131 



hp. 



c.h. 



-b.h. 



of all degrees of thickness from 6 n downward, but some of 

 the largest, in the earlier stages of rot, have brown contents. 

 These thicker, brown hyphae generally run either vertically 

 along the tracheides, or horizontally, boring through the 

 tracheide walls and markedly constricted in the bore-holes. 

 The finer hyphae, which are much more numerous, branch 

 frequently and spread in all directions, though the bore- 

 holes are nearly always transverse to the tracheide walls. 

 Hyphae may also grow up between 

 the tracheides. As decomposition 

 proceeds fewer hyphae are found, 

 but even in advanced stages of rot 

 a few colourless hyphae are gener- 

 ally present. The same variation 

 in size and colour of the hyphae 

 is also a feature of the felted my- 

 celium which fills up the cracks 

 in the rotted wood. 



Although the mycelium in the 

 wood lacks those special features 

 of interest which characterize the 

 growth of Fomes annosus and 

 Armillaria mellea, the effects pro- 

 duced in the wood are peculiar and 

 distinctive. In the first place the 

 wood is never quite delignified,. 

 and to the last will give a slight 

 reaction with phloroglucol and hydrochloric acid. At the 

 same time the cellulose, which, though present in normal 

 wood, fails to give normal reactions without special treat- 

 ment, is so far freed from lignone that rotted wood gives 

 a blue or purplish colour with chlor-zinc-iodine. Thus 

 the presence of lignone and the presence of cellulose may 

 be demonstrated, without special treatment, in the same 

 cell wall. During the process of decomposition the wood 

 also undergoes contraction to a very marked extent. In 

 the final stages this is apparent to the naked eye by the 

 large cracks and crevices, but before these appear evidences 



K 2 



FIG. 53. Mycelium of 

 Polyporus Schweinitzii in 

 the wood of the larch : &., 

 hyphal bore - hole ; b.h., 

 brown hypha ; b.p., bor- 

 dered pit ; c.h., colourless 

 hypha. 



