FUNGAL ATTACK. 73 



of the wood, and ultimately reducing it to the condition of 

 " touchwood " or "punk." "It will readily be understood that 

 all these progressive changes are accompanied by a decrease in the 

 specific gravity of the timber, for the fungus decomposes the 

 substance much in the same way as it is decomposed by putre- 

 faction or combustion, i.e. it causes the burning off of the carbon, 

 hydrogen, and nitrogen, in the presence of oxygen, to carbon- 

 dioxide, water, and ammonia, retaining part in its own substance 

 for the time being, and living at its expense. 1 



Another true parasite, Tramties radicipfrda, only attacks coni- 

 fers. Its spores, which can be readily conveyed in the fur of mice 

 or other burrowing animals, germinate in the moisture around the 

 roots : the fine threads of " spawn " penetrate the cortex and 

 spread through and destroy the cambium, extending in thin, 

 flat, fan-like, white, silky bands, and, here and there, bursting 

 through the cortex in white oval cushions, on which the sub- 

 terranean fructifications are produced. Each of these is a 

 yellowish white felt-like mass, with its outer surface covered with 

 crowded minute tubes or " pores " in which the spores are pro- 

 duced. The wood attacked by this fungus first becomes rosy or 

 purple, then turns yellowish, and then exhibits minute black dots, 

 which surround themselves with extending soft white patches. 



The many pores in the fructification of Trametes indicate its 

 kinship with the genus Polypwus, many species of which are well- 

 known as "shelf-funguses," projecting like brackets from the 

 stems of trees, and having their pores on their under-surfaces. 

 Most of these are wound-parasites. One of the commonest, the 

 yellow cheese-like Polyporus sulphur ens, occurs on Oak, Poplar, 

 AVillow, Larch, and other standing timber, its spawn-threads 

 spreading from any exposed portion of cambium into the 

 pith-rays and between the annual rings, forming thick 

 layers of yellowish-white felt, and penetrating the vessels of the 

 wood, which thereupon becomes a deep brown colour and decays. 



The ravages of such wound-parasites are often the result of 



1 Timber and some of its Diseases, by Prof. H. Marshall Ward, F.R.S., 

 to which work I am particularly indebted in the present chapter. 



