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 Schweinitzii. 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 ( 1 878) 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 eaoh 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 



