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 qf 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 



