HEART-ROT CAUSED BY OTHER FUNGI 131 
of all degrees of thickness from 6 downward, but some of 
the largest, in the earlier stages of rot, have brown contents. 
These thicker, brown hyphae generally run either vertically 
along the tracheides, or horizontally, boring through the 
tracheide walls and markedly constricted in the bore-holes. 
The finer hyphae, which are much more numerous, branch 
frequently and spread in all directions, though the bore- 
holes are nearly always transverse to the tracheide walls. 
Hyphae may also grow up between 
the tracheides. As decomposition 
proceeds fewer hyphae are found, 
but even in advanced stages of rot 
a few colourless hyphae are gener- 
ally present. The same variation 
in size and colour of the hyphae 
is also a feature of the felted my- 
celium which fills up the cracks 
in the rotted wood. 
Although the mycelium in the 
wood lacks those special features 
of interest which characterize the - 
growth of Fomes annosus and yg 53.—Mycelium of 
Armillaria mellea, the effects pro- Polyporus Schweiniteii in 
duced in the wood are peculiar and phe ae So tie at 
distinctive. In the first place the brown hypha; b.p., _bor- 
wood is never quite delignified, er pit; ¢.h., colourless 
and to the last will give a slight i a 
reaction with phloroglucol and hydrochloric acid. At the 
same time the cellulose, which, though present in normal 
wood, fails to give normal reactions without special treat- 
ment, is so far freed from lignone that rotted wood gives 
a blue or purplish colour with chlor-zinc-iodine. Thus 
the presence of lignone and the presence of cellulose may 
be demonstrated, without special treatment, in the same 
cell wall. During the process of decomposition the wood 
also undergoes contraction to a very marked extent. In 
the final stages this is apparent to the naked eye by the 
large cracks and crevices, but before these appear evidences 
K 2 
