DRY ROT, a popular name for the decay of seasoned timber and for certain forms of decay of the trees while still standing. The latter kind is caused mainly by species of shelf fungi and toadstools, which also attack the stumps of various trees. Sap rot (Polystictis verstcolor) is the rhost serious of all, destroy ing 75 per cent of railroad ties in use. Eco nomically, the former kind is the more import ant, since it attacks timber after it has been put in place in buildings. In such cases the floors or walls may collapse with more or less damage to property, if nothing worse. The fungi producing this kind of dry rot are species of the genera Polyporus and Merulius, which produce similar effects. The most common is M. lacrymans. The spores germinate in the presence of moisture and the branching threads (mycelium) penetrate as far as the wood is moist, later spreading into broad sheets and completely the fibre of the wood.
The fungus is at first white hut later turns, brownish-red, producing what is called "red-• striped') timber. Drying only temporarily checks growth, for when moisture again reaches the wood the fungus recommences its work of destruction. The wood exposed to frequent changes of moistening and partial drying is most susceptible. But if properly seasoned and then protected by antiseptic treatment or good paint, will be exempt unless the fungus has already gained entrance. In floors and walls only dry and non-alkaline sound-deaden ing substances should be used, since these do not favor the germination and-growth of the spores which may be present. Both Merulius and Polyporus are classed with the poisonous fungi.