74 THE LARCH CANKER 
thus producing an amphitheatre-like appearance in the 
wood of a transverse section. The mycelium flourishes 
chiefly in the cortex and the phloem, but can also attack the 
wood to a limited extent. 
It has been shown that this fungus is not a parasite in 
the sense in which the term is generally used. The mycelium 
does not directly attack the living cells of the host, but first 
kills them by secretions. The mycelium grows both in the 
cells of the host and in the intercellular spaces. Fructifica- 
tions are borne on the dead bark in the canker region. These 
are larger than those on the dead branches in all their parts, 
but it has been shown that this difference is due to growth 
conditions, and the dimensional differences cannot be 
made the basis of specific or varietal separation. 
Large quantities of resin are made by all attacked parts 
of the tree. This oozes out on to the surface of the canker, 
and often forms long streams down the trunk. 
Pure cultures of the fungus have been grown on various 
media, including sterilized twigs of different conifers and 
dead needles of larch, spruce, and Scots pine. In a damp 
chamber larch needles may become matted together by the 
mycelium which ramifies the mesophyll. It is suggested 
that the matting of needles on the floor of larch plantations 
may be largely due to the mycelium of this fungus, a process 
which may help in the decomposition of the foliar débris. 
Pure cultures on sterilized larch stems were grown up to 
the stage of bearing apothecia, thus completing the cycle 
from spore to spore. 
The fungus may gain admission to the living parts of the 
tree in three ways: 
1. Through wounds, which may be caused by a variety 
of agents. 
2. By growing down from the dead branches into the 
living tissues of the trunk. 
3. By means of buds which have been killed by the 
shading of the upper branches. 
It has been shown that the second of these methods gives 
