INJURIES INDUCED BY PLANTS 205 



a layer of hyphae disposed at right angles to the surface. The 

 hyphae end in somewhat club-shaped basidia, which are covered 

 by peculiar hair-like outgrowths. Only a certain number of the 

 basidia produce spores (four in each case), those which remain 

 sterile producing a new hymenium in a succeeding period of 

 growth, and in doing so they anastomose here and there by 

 lateral budding. On a transverse section a sporophore, depending 

 on its age, shows more or less distinct strata, of which only the 

 youngest possesses a pale colour, the others being of a deep 

 brown hue. When dead the whole of the sporophore appears 

 dark brown. 



STEREUM HIRSUTUM 1 * 



A very striking and characteristic form of decomposition in 

 the oak is produced by S. hirsutum. In practice such wood is 

 called "yellow piped" or "white piped." Usually a brown 

 colour first makes its appearance in certain concentric zones, 

 which to begin with are confined to one side but afterwards 

 encircle the whole of the stem, and later on a longitudinal 

 section will show detached snow-white or yellow stripes which 

 appear as white spots on a cross section (" fly wood "). When 

 the oxygen of the air has free access, as in the alburnum, 

 branch- snags, &c., the whole of the wood is frequently converted 

 into a uniform yellow mass. It scarcely seems to admit of 

 doubt that this fungus also plays an important part as a sapro- 

 phyte, and finds its way on to branches that are dying naturally. 

 In the white stripes the mycelium concerts the wood into cellu- 

 lose, and when the middle lamella disappears the elements 

 become isolated. In the yellow parts of the wood, on the other 

 hand, the solvent action proceeds from the lumen outwards, as 

 in the case of P. igniarius, and this is not preceded by a con- 

 version into cellulose. The sporophores, which usually develop 

 on the bark, appear first as a crust, but afterwards their upper 

 edge which is brown, faintly zoned, and covered with stiff hairs 

 projects in a distinctly horizontal direction. 



1 R. Hartig, Zersetzungserscheinungen, pp. 129 et seq., Table XVIII. 

 *[Very common in England. ED.] 



