4 BULLETIN 510, U. S. DEPARTMENT OF AGRICULTURE. 
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. 
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 
(PL I, fig. 3) with central or eccentric stems bearing an expanded 
cap at the top. 
The fruit bodies of the many fungi which cause decay in timber 
may vary in color from white through reds and yellows to dark 
brown or blackish. The consistency 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 pores (Polyporus, Poria (PI. 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 
