160 THE OAK 
hirsutum being all different, and in some cases so charac- 
teristic that the merest glance suffices to diagnose the 
disease (cf. figs. 42 to 45). 
There is yet another disease of oak timber to be 
noticed, and one which causes great havoc in buildings 
Fig. 44.—Oak damaged by Polyporus igniarius, a very 
common timber fungus. (R. Hartig.) 
where the ventilation is bad and the air damp. ‘This is 
the too well known dry-rot, due to the destructive 
action of the fungus Merulius lacrymans, a hymenomy- 
cete allied to the preceding, but differing from them in 
not attacking the standing timber. The spores of this 
fungus are able to infect oak planks, beams, &c.; and 
