GENERAL SUMMARY 189 



Where the Forties 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 the rhizomorphs 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 



