70 THE LARCH CANKER 
laid stress on preventing wounds when planting young 
trees; and Massee, on finding that infection could take 
place through the punctures made by Chermes abietis, 
declared that, if this insect could be suppressed, canker 
would cease to be an epidemic disease. 
All these suggestions have proved useless in obviating 
the disease, and foresters have been forced to adopt other 
means for reducing the pecuniary loss for which canker is 
responsible. One doctrine is that larch-growing should be 
confined to situations and soils which have proved capable 
of bearing healthy plantations. But since this rules out the 
majority of districts in which larch is at present grown, it 
is a confession of failure except in a few favoured localities. 
Sir Donald Munro Ferguson has adopted, at Novar, a method 
of treating larch which was described by Somerville (1906) 
in the Journal of the Board of Agriculture. He plants pure 
larch at 3,500 to the acre, the vast majority of which become 
cankered. At the age of 16-20 years he cuts out all but 
300-500 of the best trees, and is able to sell the 3,000 or so 
thinnings for £20 to £25. The lateral dead branches are 
removed and the remaining larch are underplanted with 
beech, or preferably such conifers as Picea sitchensis, Pseudo- 
tsuga Douglasii, Tsuga albertiana, Thuja plicata, Cupressus 
lawsoniana, and Abies grandis. 
In most plantations it will be possible to select 10 per cent. 
of healthy trees, and the 300-500 trees that are left may 
be exempt from canker during the remainder of their lives. 
But obviously the treatment will be impossible in woods 
where, as sometimes happens, even the best trees have three 
or four cankers apiece. Nisbet (1907) criticizes the system 
on the ground that the pure larch woods make an excellent 
breeding-ground for the fungus, and become a source of 
danger to all the intermixed larch woods in the district. 
We need therefore some method by which canker can be 
prevented, and the method of infection which I have described 
as accounting for the greater number of dangerous cankers 
suggests a treatment which may possibly prove helpful in 
preventing the disease. Until successful experiments have 
