62 THE LARCH CANKER 
fungus. After a time it will be found that at the base of 
nearly all these dead branches the fungus has spread on 
to the main trunk, and fructifications are duly made there 
(fig. 28). This shows that, when the resistance of the living 
tissues is reduced, the fungus finds no difficulty in growing 
down from the branches; and, under these conditions, 
there regularly occurs what only occasionally happens 
when the trees are alive and vigorous. It may be that 
when the tree is alive it can usually neutralize the secretion 
which the fungus pours into it through the gap, and thus 
prevent the mycelium from obtaining any foothold. 
There is another way in which Dasyscypha may gain 
admission to living stems without previous wounding ; this 
is through dormant buds which have died. There is always 
a large number of these dormant buds on a larch stem ; 
they are surrounded by a number of dead brown scales, but 
in the middle is a growing apex with the living leaf primordia. 
Given light and food these may at any time develop into 
side shoots. As the tree gets older such buds on the lower 
part die, and they immediately become attacked by germ 
tubes of Dasyscypha spores. But in a healthy tree a cork 
layer is formed beneath the buds at the time of their death, 
so that there is very slight danger of the stem bearing them 
becoming infected. In trees, however, which from lack of 
light, or other causes, are growing poorly, such buds are 
responsible for a large number of cankers. 
This source of canker, though of frequent occurrence, is 
of comparatively little importance to the forester, since it 
only affects the poorer trees in a plantation, which would 
be ordinarily removed in the first thinning. 
The importance of wounds as a source of canker. In the 
foregoing section it has been shown that there are two 
ways in which the canker fungus can gain admission to 
trees without their previously being wounded, and it is 
probable that the importance of wounds as a source of 
infection has been greatly exaggerated. The dogma that 
trees can only become cankered through wounds is due to 
Hartig’s infection experiments, for he was unable to infect 
