188 GENERAL SUMMARY 



becoming severely attacked, pruning off the side branches 

 during dry weather in the early months of the year (January 

 to March) is calculated to prevent infection to a large 

 extent. Fuller instructions for this pruning are given in 

 Chapter IV. This treatment is necessarily expensive, and 

 should be regarded as a last resort in woods which give 

 sufficient promise to render it worth while. The side 

 branches should be removed while still alive, but at an age 

 when they would normally die through the shading by the 

 crowns. If these cut branches are removed and burnt 

 there will remain very little opportunity for the saprophytic 

 development of the fungus, and fewer spores will be produced 

 for reinfection. This treatment thus lessens the chance of 

 canker in two ways : it prevents direct mycelial infection 

 from the branches into the trunk, and it reduces the number 

 of spores which might cause infection through wounds, 

 aphis pricks, and the like. The latter reason for the restric- 

 tion of canker is, however, relatively unimportant, since the 

 fungus produces spores in such enormous quantities that 

 neighbouring woods which have passed beyond the pruning 

 age will provide sufficient spores for infection. The fungus 

 is so widely distributed and so common that no hopes can 

 be entertained of stamping it out. 



The view of the predispositionist has been largely adopted 

 in the consideration of larch canker. It so happens that as 

 we recapitulate the larch diseases in the order in which they 

 have been described in this book we are forced to take up 

 more and more the attitude of the pathogenetist. Fomes 

 annosus almost certainly enters trees largely through dead 

 roots, and any treatment of the larch which discourages 

 the death of roots will also discourage the fungus, so that 

 remarks offered on the relation of larch to the soil in this 

 chapter will be more especially applicable to this fungus. 

 But it is also possible to combat the fungus by direct action, 

 by searching woods thoroughly for fructifications and by 

 destroying all diseased parts of trees. Such work can only 

 be profitable in woods in which the fungus is as yet un- 

 common, and there are many such in the south of England. 



