THE 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, &., 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 Hydnum 
diversidens. a shows the medullary rays on the tan- 
gential section; 6, a mass of felted mycelium. (R. 
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 Hydnwm diversidens, Thelephora Perdix, Poly- 
porus sulphureus, P. igniarius, P. dryadeus, and Stereum 
