132 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



shoot, if affected early, is usually killed and replaced by a lateral. 

 He then turns to the really important part of his subject, namely, 

 the origin of the more destructive cankers on the main stem. 



Mr Hiley bases his remarks on the examination of a large 

 number of cankers in trees cut down in Bagley and Tubney 

 woods near Oxford at thirteen to eighteen years of age. In the 

 large bulk of cases he has found two important features : — 



1. The cankers had been initiated at the bases of lateral 



branches. 



2. The cankers were initiated when the portion of the stem 



on which they appeared was from three to eight years 

 old. (The age was computed by counting in each 

 case the number of unbroken rings inside the canker.) 



He further found that in twenty-one out of twenty-six cases 

 examined the canker had been initiated one or more years 

 after the lateral branch died. In the remaining five cases the 

 canker was initiated during the same winter as that in which 

 the branch died. 



Since for some time after death the canker fungus usually 

 flourishes in the bark of the dead branches, Mr Hiley finds it 

 difficult to resist the conclusion that the fungus is identical with 

 that which attacks the living growth and finds its way from the 

 lateral branch to the main stem. 



It is true that the tree protects itself by forming, as the branch 

 dies, a layer of cork which extends all round the branch near its 

 base, turning inwards and so uniting the cork envelope to the 

 woody centre and covering in the cortex and phloem which 

 would otherwise be exposed. But Mr Hiley thinks that the 

 fungus makes its entrance at the point where the new cork layer 

 joins the wood. The space, he says, though narrow is frequently 

 large enough, and though he has never been able to trace the 

 hyphae right through it, he has seen hyphas at each end of it. 

 He also thinks it possible, though less likely, that the fungus 

 may effect an entrance through the wood itself which, until the 

 dead branch decays, continues to project beyond the cork barrier. 



Mr Hiley observes that if dead branches are, as he suspects, 

 the chief source of canker, this new conception will suggest 

 considerable modifications in the method of larch cultivation. 

 He advises that experiments should be made in the removal of 

 dead and suppressed branches. Since the knife exposes the 



