THE CULTIVATION OF THE OAK 



159 



cases some of the fungi destroy the vessels, fibres, 

 fee., 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 Hydnwni 

 diversidens. a shows the medullary rays on the tan- 

 gential section; b, a mass of felted mycelium. (B. 

 Hartig.) 



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 diversidens, Thelephora Perdix, Poly- 

 porus sulphur eus } P. igniarius, P. dryadeus, and Stereum 



