POLYPORUS. 435 



side is concentrically marked, and has a stoue-hard coating which 

 is generally more or less cracked ; several zones and layers of 

 tubes will be found when the sporophore is cut in section. 



This fungus produces a white-rot in the wood, and is one of the 

 most common and dangerous of wound-parasites. The wood 

 attacked by the mycelium is at first dark in colour, then 

 yellowish-white and soft. According to Hartig, a delicate 

 mycelium fills up the elements and eats away the inner layers 

 of the walls : then the middle lamellae are transformed into 

 cellulose and al)Sorl)ed I)y it (Fig. 264). 



Polyporus fomentarius (L.) (Fomes fomcntcfrins (L.) Fr.) ^ 

 (Britain and U.S. America). " Tinder-fungus." Sporopliores 

 broad and shaped like reversed brackets or hoofs. Their upper 

 side, at first brownish and velvety, becomes afterwards smooth, 

 grey, and marked with broad concentric zones. The margin 

 is rounded and uniformly grey. The pore-layer is smooth and 

 greyish-brown. A longitudinal section shows a homogenous 

 tinder-like mass, covered on its lower surface by layers or 

 zones of pores. 



The tinder-fungus is parasitic on beech, elm, and mountain 

 maple. It is particularly common in l)eech-fo rests, and was 

 even more so at one time when the infected trees were allowed 

 U) remain standing. The sporophores may be found on living 

 stems, on remnants of trees broken by wind, and on felled 

 trees. For some distance above and below the seat of the 

 sporophore runs a furrow on the stem, marking a tract where 

 the mycelium has penetrated to the cambium and killed it, so 

 that growtli in thickness ceases (Fig. 2 60, a). 



The mycelium causes in the wood a white-rot of a light 

 yellow colour. Where the wood is still firm, though diseased, 

 it will be found to be divided into cubical portions by white 

 tracts of mycelium which run both radially and vertically. A 

 \ery characteristic feature of the destruction consists of l)road 

 white leathery bands of mycelium, formed in a radial direction 

 through the wood ; these are l)est seen on stems shattered by 

 storm, or on wrought timlier.2 



•Rostnip, TkhskriJ't pa Skovburg, 188.3. Tubeuf, " Mittlieilungen," A/foj. 

 For,rtf-. u. Jar/d-Zeituug, 1887. A common British species. (Edit.) 



-Krull (Sckles. Ge.s. f. vaterland. Knit., 1893) distiugiiishes a gelatinous niyfeliuin 

 and a cushion-mycelium. 



