138 HEART- ROT CAUSET) BY OTHER FUNOl 



The fungus jiroduces a red rot in the duramen of the 

 larch, which spreads indefinitely both upwards and down- 

 wards from the point of infection. My OAvn 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 Schweinilzii . They differ, however, in show- 

 ing more regular tangential and transverse cracks, so that 

 j)ortions bi'oken away are more nearly cubical. These 

 blocks are heavier and firmer than wood rotted b}^ P. 

 Schweinitzii, and have a darker and jicher chestnut colour. 

 The process of decomposition does not appear to have been 

 described in the larch, though the fungus was carefully 

 investigated b}^ Hartig (1878) on the oak. Schrenk's observa- 

 tions on the spruce (19U0), although they cannot be appli- 

 cable to the larch in all details, should be briefly noted in 

 tliis connexion. 



First the wood turns shghtly 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 ling 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 

 ill the tracheide walls, similar to those shown in lig. 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 

 j-ays 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 

 lirst-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 



