158 ARMILLARIA MELLEA, 
to indicate a stage of excessive vigour in the mycelium, and 
‘though it does not directly cause marked changes in the 
character of the wood, it appears in some way to transform 
the wood into a state in which it is easily acted on by the 
hyphae behind. ; 
The dark-brown pigment differs from that found in the 
black specks of wood rotted by Fomes annosus in being 
unaffected by hydrochloric acid, though it is bleached by 
concentrated nitric acid. 
When two black lines approach each other they seldom 
unite, but cease to move when about 1 to 5 mm. apart. 
This causes the frequent phenomenon of a pair of black 
lines running parallel to each other. In some parts a black 
line is replaced by a much broader band of colourless, 
bladder-like hyphae. These resemble the black-line hyphae 
in all respects except their colour and the thickness of their 
walls, and apparently are much more slowly decomposed. 
They may cover a width of as much as 6 to 10 tracheides. 
Resin flow. The disease is generally accompanied by an 
external flow of resin, and sometimes the quantity of this 
substance excreted is so great that the fallen needles, twigs, 
and soil round the base of the trunk become compacted 
into a hard adherent crust. The resin arises in two ways. 
Firstly, the living cells lining the resin ducts in the cortex 
and wood are killed so that the contained resin escapes, 
and, taking advantage of the cracks formed by the drying 
of the bark, runs down the outside of the trunk. Secondly, 
the living tissues in the neighbourhood of the fungus excrete 
an abnormal amount of resin, and wood which is formed 
after some part of the tree has been attacked is characterized 
by containing a large number of irregular resin ducts, so 
that in this respect the wood resembles the abnormal wood 
made in the region of a canker. On account of this escape 
of resin the disease is sometimes known under the name of 
‘resin flow’ or ‘resin glut’, and though the flow of resin 
is commonly not so great in the larch as in the Scots or 
Austrian pine, it is often the first external symptom of the 
disease. 
