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. (K. 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 



