160 THE OAK. 



Mrsutum being all different, and in some cases so char- 

 acteristic 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. (E. 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 hymenomycete 

 allied to the preceding, but differing from them in not 

 attacking the standing timber. The spores of this 



