56 THE LARCH CANKER 



indication of being suppressed. The trees were cut down 

 and the parts containing the cankers were brought into 

 the laboratory. Here the cankers were sawn through 

 transversely and the surfaces planed or smoothed with 

 a sharp knife until the section was reached where the 

 cambium had first been killed. 



The inspection of these cankers confirmed the two 

 important observations that in the large bulk of cases : 



(i) The cankers had been initiated at the bases of lateral 

 branches. 



(ii) The cankers were initiated when the sections of stem 

 were, from three (occasionally two) to eight (occasionally 

 nine) years old. 



We must thus consider in detail the condition of affairs 

 which exists at the bases of lateral branches on those parts 

 of the tree which are from two to nine years old. 



In an ordinary ten-year-old larch plot planted at 3 X 

 3 ft., the weaker shoots die off when two or three years old, 

 the stronger shoots when five, six, or even eight years old. 

 In younger plantations, before the branches have begun 

 to shade each other, all of them may remain alive, but 

 generally some small dead branches will be found at the 

 base of the trunk, especially when they have been smothered 

 by rank grass and weeds. Thus the part of the tree which 

 is from two to eight years old, in which cankers are generally 

 initiated, is also that part where some or all of the lateral 

 branches have lately died. Further, in nearly all woods 

 the lateral branches become infected with Dasyscypha 

 calycina, which grows saprophytically on them as soon as 

 they are dead, and continues to flourish on them for three or 

 more years, filling all the dead bark with its mycelium. 



When a dead branch is seen projecting from a canker it 

 has generally been supposed that the canker has killed the 

 branch, but it may equally be true that the fungus spreads 

 from the dead branch and causes the canker. In order to 

 determine this it was necessary to notice the relative times 

 at which the branch died and the canker was initiated. 

 The date of the death of the branch may readily be deter 



