28 THE LARCH CANKER 
an anastomosing mass of hyphac. In this case a red-brown 
stain is formed in the centre of the stem, irregularly star- 
shaped in section and continuous on one side with the 
canker, but spreading for a short distance above and below 
it in the heart-wood. 
The hyphae are colourless and of markedly varying 
width ; they pass through the tracheide walls by very fine 
bore-holes, which are usually accurately transverse, but 
may be somewhat oblique or may even be transverse on 
one side of the middle lamella and oblique on the other. 
The whole mycclium in this region is evanescent and ‘does 
little damage to the wood. 
An interesting phenomenon in connexion with this attack 
is the formation of a gum by the infected wood. This gum 
has been worked out more in detail in connexion with the 
larch heart-rot which also stimulates its formation. 
Under the influence of fungal attack the tissucs show 
certain changes which must be described in detail. 
(i) The walls of all the cells in the neighbourhood of the 
mycelium turn brownish vellow in colour ; frequently their 
contents arc modified ; the protoplasm becomes markcdly 
vacuolated, and the nuclei lose their rounded outline. 
Large accumulations of crystals of calcium oxalate, both of 
the mono- and tri-hydrated form, appear in the cortex, 
and crystals of the trihydrated form become much more 
frequent in the phloem parenchyma, and may also occur 
in the medullary ray cells. Large quantities of resin are 
formed in all cells, much more than can be contained in 
the resin cysts, so that all the tissues become saturated 
with it. The tannin content is also increased. Tannin and 
resin are probably products of excessive katabolism, show- 
ing that the protoplasm of the cells has respired to an 
abnormal extent, only ending in death. The calcium 
oxalate may arise partly in this way, though as shown 
below it is also excreted from the fungus. 
These phenomena are not confined to the cells which 
cither contain hyphae or have hyphae touching them; but 
all the cortical and phloem tissue, for a thickness of about 
