1916] FoMES OFFICINALIS (Vill.) 203 
PATHOLOGICAL. 
Polyporus officinalis is the cause of a red heart rot of the stem of 
conifers. The affected wood darkens to a reddish brown, becomes ex- 
ceedingly friable, and fractures into rectangular blocks up to an inch 
in diameter in some species. In the case of Pinus strobus the wood 
fractures into much smaller pieces, down to one-eighth of an inch, 
and cracks longitudinally both tangentially between annual rings and 
radially. The crevices or spaces in the fractured wood are soon occu- 
pied by sheets of mycelium, so that the diseased wood presents a very 
characteristic appearance—resembling that caused by but one other 
species, namely Polyporus sulphureus, differing from that form, however, 
by a more abundant production of softer sheets. The mycelium may 
wholly disappear in weathered material, or in decayed wood of long 
standing—the resemblance then being to the rot caused by Polyporus 
Schweinitzii or Lenzites sepiaria (Fig. 12). Figs. 7-10 are illustrations 
of decayed white pine, Fig. 11 of Douglas fir. Fig. 8 is a photograph of 
the radial longitudinal face of a block in the plane of a sheet of mycelium, 
and shows well the extent of the fracturing of the wood, and also stages 
(particularly at the left) of the filling in process by the fungus. These 
transverse smaller cracks involve most commonly but a single annual 
ring. Reference to Figures 9 and 1o show that there are likewise many 
small corresponding radial checks. An examination of sections from 
blocks embedded in celloidin reveals the presence of still smaller checks, 
sometimes affecting only a few elements (Fig. 14). 
It has already been stated that the fungus seems capable of a more 
or less complete destruction of pine wood in localized spots in the trunk 
—resulting at times in the formation of mycelium-filled cavities. This 
is due, not to the entire digestion of the wood, but to the tendency of 
the wood to check indefinitely and to the vigour of the mycelium. A 
study of Figures 9 and 10 is convincing that such destruction may 
take place. Tiny fragments of wood are embedded in the thickest 
sheet. Fig. 6 is a photograph of the cut surface of a large mass taken 
from a pine trunk and represents plainly an almost solid structureless 
matrix of mycelium in which fragments of wood of various sizes are 
embedded. It is possible, and seems probable that in time the digestion 
may be complete, but the consumption of the residue of the walls after 
the cellulose has been removed is slow. In this connection Text-figure I 
is interesting, taken from a celloidin section of white pine and showing 
the destruction of the tissues in the neighbourhood of a resin canal. 
The space around the canal was occupied largely by a dense mass of 
mycelium, hyphae from which extended into the surrounding tracheids. 
Such occurrences are not infrequent in the pine I have examined. 
