84 HEART-ROT 



when the rot reaches the trunk it spreads both upwards 

 and downwards. There is some doubt as to the method of 

 infection adopted by Poria vaporaria, but probably, like 

 Polyporus sulphureus, it can only reach the heart-wood 

 through wounds. 



Fomes annosus, (Fr.) Cooke : General. In Britain Fomes 

 annosus attacks nearly all kinds of conifers. It has, how- 

 ever, two different modes of attack, and as the symptoms 

 are very distinct in the two cases, they might easily be 

 considered the work of two different fungi. In one case the 

 fungus attacks the trees when young, usually about four 

 to ten years, and kills them in a year or two. Frequently 

 in young plantations individuals or groups may turn a brown 

 or reddish-brown colour, lose their leaves and die, and on 

 pulling these trees up it is generally found that the roots 

 are attacked either by Armillaria mellea or Fomes annosus. 

 The identity of Armillaria mellea can generally be detected 

 by the presence of rhizomorphs and the large flaky masses 

 of mycelium between the wood and the phloem and between 

 the scales of the bark of the rootstock, as well as by the 

 resin flow at the base of the trunk. Fomes annosus is not 

 so easy to identify unless some of the perennial fructifications 

 are present, but small pustules of mycelium on the roots 

 and the very thin layers of mycelium in the bark, no thicker 

 than the thinnest tissue paper, are usually sufficient evidence 

 of its presence. The species that are most commonly 

 attacked in this way are Douglas fir, Lawson's cypress, 

 Weymouth pine, and sometimes the monkey-puzzle tree, 

 but probably many other conifers are liable to this kind of 

 attack. In such instances the fungus is a fairly rapid 

 parasite, and death follows quickly on attack. Other 

 species, such as the larch, 1 spruce, and Scots pine, are not 

 generally attacked by the Fomes until they are comparatively 

 old and have made heart- wood. On these trees the fungus 

 is a rather feeble parasite and kills living tissues very slowly. 

 It flourishes, however, in the heart-wood which is dead, and 



1 The death of some young larch trees in the manner described above 

 ia reported by Somerville (1898). 



