GENERAL SUMMARY 189 
Where the Fomes has obtained a thorough hold, the only 
means by which it can be combated is by sylvicultural 
methods which improve the soil, especially the subsoil. 
Probably the same recommendations. apply to Polyporus 
Schweinitzii, but so little is known about the pathology of 
this fungus that it would be unwise to dogmatize. 
Polyporus sulphureus and Trametes Pini, which also cause 
heart-rot, begin near the top of the tree instead of at the 
roots. They enter chiefly through wounds left when large 
living branches are broken by the wind or other means, and 
the fungi are consequently most common in open places or 
near the edge of plantations. As soon as these diseases are 
discovered by the presence of fructifications the trees should 
be cut down and diseased portions, as well as the fructifica- 
tions, burnt. 
The honey fungus, Armillaria mellea, is probably the 
most destructive pest with which British forestry has to 
contend. It can kill all species of conifers and a great 
many broad-leaved trees as well, and in many woods it is 
so common that its eradication is wellnigh impossible. 
By means of spores the fungus attacks the dead stumps of 
trees, chiefly broad-leaved species such as oak and beech. 
On large stumps it may feed for a great number of years, 
and it sends rhizomorphs out into the soil, which grow into 
the roots of conifers, with which they come into contact, 
and in a few years kill the trees. From such conifers fresh 
rhizomorphs arise until the ground may become infested 
with the fungus and the pathologist comes to wonder, not 
why so many trees are killed, but why so many escape. 
Probably therhizomorphs are incapableof infecting a healthy, 
living root, and can only enter through. wounds or dead 
roots, so that dead roots predispose the trees to attack, and 
thus far correct soil treatment may minimize the incidence 
of attack. But old trees must generally have some dead 
roots, and when the fungus is present a large percentage of 
deaths must be anticipated. Eradication of the fungus, 
though difficult, is well worth attempting where it is not very 
widespread. The means to be adopted have been described 
