hirsutum being all different, and in some cases so characteristic 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 hymenomycete allied to the preceding, but differing from them in not attacking the standing timber. The spores of this