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- 

 nitzii. 



(iii) 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. 



