POLYrOKUS. 



U9 



but later becomes brown, and, on being touched, deep reel. Tlie 

 spores are white, and various forms of hairs occur among the 

 basidia. Young sporophores appear as little brown cushions on 

 felled timber, also on living stems of pine, and, according to 

 Magnus, on Weymouth pine. 



The disease generally makes its first 

 appearance in roots and lower parts of the 

 stem, spreading thence into higher parts. 

 Diseased wood has a characteristic odour of 

 turpentine ; it has a reddish-brown colour, 

 and, as destruction proceeds, it gradually 

 shrinks and dishitegrates till it becomes so 

 soft as to be easily powdered between the 

 fingers. Where broken over, the wood is 

 often covered with a thin white coating of 

 mycelium incrusted in resin so as to appear 

 like chalk. 



The mycelium penetrates the cell-walls 

 in all directions. A very characteristic 

 feature of this parasite is furnished by 

 shrinkage-fissures in the thick walls of the 

 tracheids of the summer- wood (Fig. 280). 

 These are numerous and run upwards from 

 right to left extending through the whole 

 wall to the outermost layers. They differ 

 from the fissures in tracheids destroyed by 

 P. raporarii(s, in that they run round the 

 whole circumference of the cell, instead of 

 being small and set vertically above each 

 othei-. 



Polyporus (Fomes) pinicola (Sw.) (U.S. 

 America). Sporophores thick, hoof-like or 

 bracket-shapeil, with a smooth dark-grey upper side and a bright 

 red rounded margin. The hymenial layer is smooth and yellowish, 

 the spore-powder white. In section the sporophores are white. 

 The species is frequent on living stems of spruce, pine, and fir, 

 also on birch and cherry. 



Polyporus (Fomes) marginatus Fr. (U.S. America). Sporo- 

 phores with red margins, and otherwise very like those of the pre- 

 ■ceding species, yet generally much larger, and more extended. 



2f 



Fio. -280. — Tracheid of 

 P(>w«destroyed by Polt/iiorun 

 .lixtoti-'iiiouhf. The celbilose 

 has been for the most part 

 extnicted, and the waU« con- 

 sist of lignin (wood -gum). 

 Cracks occur in the dry 

 secondary wall, while the 

 wall (o, 0) remains intact. 

 The spiral structure of the 

 secondary wall causes cross- 

 ing of the fissures in the 

 walls of adjoining cells at 

 tlie bordered pits, e, and at 

 bore -holes, d, e ; where 

 neither pits nor holes are. 

 present the fissures are 

 simple,/; (After H. Hartig.) 



