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 willremain 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. 
