138 HEART-ROT CAUSED BY OTHER FUNGI 
The fungus produces a red rot in the duramen of the 
larch, which spreads indefinitely both upwards and down- 
wards from the point of infection. My own observations of 
the rotted wood have been confined to a section from the 
base of a large trunk in the School of Forestry Museum at 
Oxford. This section (fig. 66, p. 155), which came from. 
Windsor Park, is hollow, and only small fragments of rotted 
wood remain attached to the uninjured wood surrounding it. 
These fragments are in many respects similar to wood rotted 
by Polyporus Schweinitzit. They differ, however, in show- 
ing more regular tangential and transverse cracks, so that 
portions broken away are more nearly cubical. These 
blocks are heavier and firmer than wood rotted by P. 
Schweinitzii, and have a darker and richer chestnut colour. 
The process of decomposition does not appear to have been 
described in the larch, though the fungus was carefully 
investigated by Hartig (1878) on the oak. Schrenk’s observa- 
tions on the spruce (1900), although they cannot be appli- 
cable to the larch in all details, should be briefly noted in 
this connexion. 
First the wood turns slightly red brown, but in longi- 
tudinal cuts it is seen that this colour is confined to irregular 
patches. Then small transverse cracks appear which never 
cross from one annual ring to the next, but extend part way 
across a ring either from the side of the summer or spring 
wood. At this stage microscopic sections show numerous 
small breaks and fissures, which are evidence of much 
shrinkage having occurred in the wood. Slanting fissures 
in the tracheide walls, similar to those shown in fig. 54, 
were also observed in the spruce, but they are said to rise 
from left to right at an angle of about 45°. The medullary 
rays are often absorbed, so that the tracheides appear dis- 
torted in tangential sections. Later the annual rings separate 
from each other, presumably owing to the destruction of the 
first-formed spring wood in each ring, and the radial fissures 
become complete, so that the wood becomes divided into 
a number of long flat slabs, each the width of an annual 
ring. There is very little mycelial development in the 
