Tllti CULTIVATION OF THE OAK 159 



cases some of the fungi destroy the vessels, fibres, 

 &c., by dissolving their walls from inside, while others 

 destroy the part common to contiguous cells, &c., and 

 thus first isolate the elements and then complete the 

 destruction. A series of very interesting researches by 



FIG. 43. Oak timber destroyed by the fungus Ilydnum 

 (lircrxidens. a shows the medullary rays on the tan- 

 gential section; &, a mass of felted mycelium. (R. 

 liar tig.) 



Hartig has demonstrated that the presence of these 

 timber-destroying fungi can be detected from the mark- 

 ings and discolorations they produce in the wood ; those 

 due to Hydnum div&rsidens, Thelephom Perdix, Poly- 

 porus sulpliureusj P. igniarius, P. dryadeus, and Sterenm 



