124 HEART-ROT 
with the increment borer, and be prepared to clear fell as 
soon as they reach a remunerative size. The.poles can then 
be sold for pit props, for which purpose a little heart-rot is 
not a serious blemish. 
No means of artificially aerating the subsoil is economi- 
cally possible. I have seen larch plantations on land that 
was previously common, where the ground was said to have 
been double-dug before planting. Heart-rot was not very 
serious, but it was unmistakably present. Double-digging 
will at most affect the top 16 in., and aeration must go down 
much deeper than this in order to prevent pumping. Natural 
aeration may, however, be encouraged by planting deep- 
rooting trees such as oak or false acacia. In Germany, 
lupin is also used on heaths for this purpose, and is allowed 
to grow for a few years before planting trees. 
Destroying all fructifications will no doubt have a palliative 
effect, especially in woods where Fomes annosus is not yet 
abundant. It removes, at any rate, one of the sources of 
infection, and we know that spores are made in great 
quantities where fructifications are allowed to appear. In 
looking for them it should be remembered that they are 
‘borne particularly on the trunks of dead conifers. They 
are always formed near the base, and are often quite hidden 
in the débris of leaves, twigs, and weeds that surround the 
trunk. By treading lightly all round the tree their presence 
can often be discovered. 
The remains of rotted trees should be burnt whenever it 
is possible, but grubbing up stumps is so expensive that 
woods can seldom be effectively cleared in this way. In 
some cases, however, such trouble will be well repaid. 
There is one wood which I have kept under observation for 
many years without ever finding Fomes annosus. The wood 
is a fairly large one, and in the last twenty years conifers 
have been widely planted in it. Previously it was almost 
exclusively composed of broad-leaved trees. This year 
(1919) a Corsican pine was found dead and fallen down, 
and from its roots I picked the fructification shown in 
fig. 40. This pine is almost surrounded by larch trees. 
