130 HEART-ROT CAUSED BY OTHER FUNGI 
more confined than in the larch (compare fig. 49 with 
fig. 52). This suggests that the fungus is purely sapro- 
phytic. At the same time dead trees are not infrequently 
found which have become rotted through to the bark, and 
it is only then that fructifications are borne on the trunk, 
except when large branches have fallen away so as to expose 
the heart-wood. For the present it must remain an open 
question whether such dead trees are killed by other causes, 
or whether P. Schweinitzii can kill the roots, taking advan- 
tage of the more moist conditions in the soil, and thus, 
secondarily, produce suitable conditions for growth in the 
sap-wood of the stem. 
In the earliest stages of rot, the heart-wood has a rather 
deeper red colour than normally, but it soon loses its reddish 
tinge and takes on more the colour of cork (fig. 50). It 
also becomes very much lighter in weight. Further decom- 
position’ is generally attended by deepening of the colour 
(fig. 49), in which case the wood becomes dark walnut 
brown, and has a strong smell of turpentine. It cracks 
along transverse, radial, and tangential planes, producing 
wedge-shaped or cubical blocks which can be picked out 
with the fingers. The cracks are often filled with mycelium 
of the fungus, bound together with resin and of cheesy con- 
sistency. If a section of a trunk cut in this stage is kept 
in a dry laboratory the rotted wood contracts on drying to 
such an extent that small pieces fall away by their own 
weight, and the section is eventually left with a hollow 
centre. The wood is then so far reduced in weight that, 
according to Hartig, its specific gravity is only 0-19, as 
compared with 0-57 for normal wood. 
With the help of a microscope mycelium can be found in 
the wood from the earliest stages of rot. But dense agglome- 
rations of hyphae, such as occupy the regions of most 
intense wood destruction in Fomes annosus and Armillaria 
mellea, are nowhere present in wood rotted by this fungus, 
except in the cracks as mentioned above. Consequently, 
decomposition is less localized and more evenly distributed. 
The hyphae present in the wood are mostly colourless and. 
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