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 Porta vaporaria, but with 
increasing age the two fungi may be readily distinguished 
by the fact that with Merulius they become grey and silky 
ve dt 
n= i] ad 
Fie. 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 ; ¢, 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 Porta. 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 sulphureus, 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 
Trametes 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), 
