442 



I'.ASIDIOMYCETES. 



rays appear snowy white at the place where the two forms 

 of rot meet ; this is due to an accumulation of starch left 

 after the cell-walls liave been almost completely dissolved. 



Polyporus (Poria) vaporarius (Pers.)^ (Britain and U.S. 

 America). Tlie sporophores are white, and have a pungent 

 odour ; they form crusts (never l)rackets) closely adherent to 

 dead sul)strata, especially to l)eams and other timber in buildings, 



m 



Irnkm 



Fig. 273.— Polyporus dryadeus. Later 

 stage of decay of Oak-wood. The darker 

 places still consist of firm brown wood ; 

 the white, however, are soft cellulose, 

 (v. Tubeuf phot.) 



^«-f" 



Fio. 27 i.— Polyporus dryadeus and Poly- 

 porus igniarius. Destruction of Oak- 

 wood under the combined agency of 

 both fungi. The wood is yellowish and 

 perforated ; the medullary rays are 

 snowy-white, from the accumulation of 

 unchanged starch, (v. Tubeuf phot.) 



where this fungus does great harm. They are also found, how- 

 ever, on bark of living stems of spruce and fir. The destruction 

 takes the form of a red-rot, the wood attacked becoming red- 

 Itrown, cracked, and soft. The mycelium is found in stems and 

 roots of trees ; in cracks in the wood and below the bark, and 

 on the surface of timber in buildings, it forms fan-shaped strands 

 of a permanent white colour. The mycelial strands of the 

 "dry-rot fungus" {Mending lacrijiiunis) dilfer from it in being 



Very common in Britain on dead wood, less so on living trees. (Edit.) 



