HEART-ROT CAUSED BY OTHER FUNGI 135 
filled up with mycelium as with the latter fungus. But 
wood rotted by Poria vaporaria may be distinguished by 
the following features : 
(i) The rotted wood has the consistency of charcoal, 
for which it might be mistaken but for its red- 
brown colour. 
(ii) It has not the turpentine smell which is so charac- 
teristic of wood rotted by Polyporus Schwei- 
nitzit. | 
(ui) The mycelium in the crevices is not chalky, but 
woolly, and the mycelium is partly composed 
of white mycelial veins, which are made up 
of numerous parallel, thick-walled, slightly 
branched and sparsely septate hyphae. These 
veins grow not only in the crevices, but also 
on the outside of blocks of wood, where they 
are kept damp, and between the wood and 
bark of dead trees. 
The microscopic features are also similar to those of 
Polyporus Schweinitzii. The hyphae, which are not numerous 
in the tracheides, are some thick-walled and some thin- 
walled, are poor in branches, and are constricted where 
they bore through the tracheide walls. But the bore-holes 
are characteristic in that the hyphae digest the middle 
lamella across a greater breadth- than the rest of the wall, 
as shown in fig. 55, B, so that the bore-holes are somewhat 
lens-shaped and in surface view appear to be surrounded 
by one or more nearly concentric circles. In the summer 
wood there are numerous cracks in the tracheide walls 
similar to those caused by Polyporus Schweinitzii, but not 
as a rule so long. The hyphae frequently have ‘ buckle 
connexions ’ at the points where septa are formed (fig. 55, A). 
This rot may either spread up from the roots or may be 
initiated above ground where the heart-wood is exposed by 
the fall of a branch. 
As stated above, there are many varieties of this fungus, 
the distinctive features of which are only partially known. 
