158 ARMILLABIA MELLEA, 



to indicate a stage of excessive vigour in the mycelium, and 

 tliough 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 

 concentiated 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 otlier. 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 mdth of as much as 6 to 10 tracheides. 



Resin flow. The disease is generally accompanied by an 

 external How of resin, and sometimes the quantity of this 

 substance excreted is so gieat 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 dryhig 

 of the bark, runs down the outside of the truidi. Hecondly, 

 the living tissues in the neighbourhood of the fungus excrete 

 an abnoinial amount l)f resin, and wood which is formed 

 after some pa it of the tree has been attacked is characterized 

 by containing a large numlxT of irregular resin ducts, so 

 that ill this respect the wood resembles the abnormal wood 

 made in the I'cgion of a canker. On account of this escape 

 of resin the disease is sometimes known undei- the name of 

 ' resin flow ' or ' resin glut ', and though the flow of resin 

 is commonly iKjt so great in the larch as in the Scots or 

 Austrian pine, it is often the first external symptom of the 

 disease. 



