4 BULLETIN 510, U. S. DEPARTMENT OF AGEICULTUKE. 



Air. — Under ordinary conditions the air supply within and sur- 

 rounding the timber is amply sufficient for decay. Fungi develop 

 best in still air in closed spaces, but this is due to the greater humidity 

 rather than to air requirements, for a good air circulation dries the 

 timber to a point unfavorable to the development of the organisms. 



In the case of timber thoroughly saturated with water, however, 

 so that the cell cavities are filled with the liquid, decay is prevented 

 entirely through lack of sufficient oxygen. 



I FRUITING BODIES. 



Fruiting bodies are an expression of fungous activity within the 

 wood., They form only after decay has well started. They appear at 

 the surface in the form of single or imbricate shelves or brackets, 

 leathery or waxy incrustations, or, in a few cases, as mushrooms 

 (PI. I, fig. 3) with central or eccentric stems bearing an expanded 

 cap at the top. 



The fruit bodies of the many fimgi which cause decay in timber 

 may vary in color from white through reds and yellows to dark 

 brown or blackish. The consistenc}' or texture is also highly vari- 

 able, from fleshy to tough and leathery, and occasionally hard and 

 woody. In some species the under side, or outer surface where the 

 fungus is spread out as a crust (resupinate), is smooth (Stereum, 

 Corticium, Peniophora, Coniophora (frequently warted)). In other 

 cases, the under side, or the outer surface where resupinate, bears 

 numerous por.es (Polyporus, Poria (PL II, fig. 5), Merulius, Tra- 

 metes, Daedalea, Fomes). Still other species have platelike gills on 

 the under side (Schizophyllum, Lentinus, Lenzites). Occasionally, 

 forms with distinct spines (PL I, fig. 4) or teeth are encountered 

 (Hydnum). Various other species are illustrated in Plates III 

 toX. 



HOW WOOD-DESTROYING FUNGI SPREAD. 



There are two general methods by which wood-destroying fungi 

 spread from infected to sound timber : (1) By a direct overgrowth of 

 mycelium from an infected stick to adjoining or near-by timber, and 

 (2) by the blowing about of spores produced by the fruit bodies or 

 by the mycelium. 



Infections by mycelium. — In wholly or partially inclosed moist 

 spaces, such as are often found in the basements of buildings, in 

 mines, or beneath low, poorly ventilated lumber piles, the mycelium 

 finds sufficient moisture in the air to allow it to develop on the 

 surface of timbers, and in this way. may progress along the timber 

 for considerable distances. Such may be the case also where timber 

 is close piled; the writer has records where severe infections have 



