432 



BASIDIOMYCETES. 



over it a new hymenium ; this is continued for some time so 

 that the sporophore consists of successive layers, and the spiny 

 outgrowths become much thickened. Infection, as was experi- 

 mentally shown by Hartig, takes place on wounds. 



The wood-destruction, consisting of a white-rot, was studied 

 by Hartig, chiefly on the oak and beech. It begins by the 



Fig. 262. — Poly-porus igniarius. Causing death of a White Alder plantation at 

 Petneu, Stanzer Thai, Tyrol. The stems bear sporophores, and die from above 

 downwards, (v. Tubeuf phot.) 



appearance of yellowish longitudinal bands (not white as with 

 Stereum hirsutum), and extends gradually till the wood becomes 

 uniformly yellow. The mycelium causes the inner layers of 

 the cell-walls to swell gelatinously without previous transfor- 

 mation into cellulose, and finally to dissolve out leaving the 

 middle lamellae longest intact. 



