136 HEART-ROT CAUSED BY OTHER FUNGI 



One form causes a ' dry rot ' on structural timber not 

 unlike that produced by the dreaded Merulius lacrymans. 

 Both occur in houses, especially in cellars and other damp 

 or ill-ventilated situations, and rot the woodwork to such 

 an extent that it collapses under any strain that may be 

 put upon it. Surfaces of the rotting wood are often covered 

 by a thickish layer of felty mycelium traversed by veins of 

 denser conducting hyphae. Such layers are made by 

 Merulius lacrymans as well as Poria vaporaria, but with 

 increasing age the two fungi may be readily distinguished 

 by the fact that with Merulius they become ^rey and silky 



FIG. 55. Poria vaporaria : A, hypha, showing buckle connexions ; 

 a, early stage showing how the connexion grows out from one side of the 

 septum ; b, later stage, in which the wall between the connexions and the 

 part of the hypha on the other side of the septum has been absorbed. 

 B, hyphal bore-hole ; c, in section ; d, in surface view. 



on the surface, whereas with Poria they remain white and 

 felt-like. These mycelial layers are very like those found 

 in the open on trees attacked by Poria. But the humid 

 conditions and large area of wood surface afforded by the 

 under-side of an ill -ventilated floor, or similar situation in 

 a building, allow of a much more massive mycelium than 

 is generally found in the forest. 



Polyporus sulphurous, Fr. We now come to two fungi 

 which, though they cause heart-rot in the larch, are definitely 

 wound parasites, and infect the tree through sub-aerial 

 wounds or dead branch snags left by the fall of the larger 

 branches. These two fungi are Polyporus sulphureus and 

 JTrametes Pini. 



Neither of these fungi has yet proved very destructive 

 to the larch in Britain, and with the former, at any rate, 

 little fear need be entertained as to its power for evil in 

 well-regulated woods. The sulphur polypore has been 

 found in Europe on oak, locust (Robinia pseudacacia), 



