HEAET-ROT 99 



If the rotted wood remains wet (and it is often saturated 

 with water), it may become sodden and still more decom- 

 posed. It is very probable that bacteria assist in this final 

 stage, and the large amount of cellulose present would be 

 suited to bacterial action if enough moisture were present. 



The myceHum grows up the trunks much more rapidly 

 than it spreads transversely, since the gum layer limits 

 lateral expansion. The affected part of the wood may be less 

 than half an inch in diameter, but up to 4 or 5 ft. in 

 length. If the rotted portion could be dissected out it would 

 then appear as a long spike. Later the fungus grows up 

 from other basal points, making fresh spikes, and when 

 a number of these are cut across in a transverse section, 

 a beautiful pattern is often produced. Fig. 36 is a photo- 

 graph of such a section, cut somewhat obhquely ^dth an 

 axe. In the rotted portions the white cellulose patches can 

 be seen, and the dark gum lavers round the individual 

 ' spikes ' of rotted wood are also visible. Another common 

 type of rot is showii in fig. 31. Here an annular portion 

 is rotted and a central peg of sound wood remains, wliich 

 is of course protected by a layer of insolu])le gum. Tiiis 

 central peg is often present, and may be no thicker tlian 

 a pencil, though as much as 5 ft. long. 



ii;: 



