30 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 
The hyphe attack the cell walls very slightly, presumably living on 
the tannin, of which oak wood contains a high percentage. The 
value of the wocd for veneers is very much enhanced. The writer 
has no record of this discoloration being found on oaks in this 
country. 
: DECAY DISCOLORATIONS. 
The hyphe of wood-destroying fungi ving within the wood feed 
on the various substances composing the cell walls. They use certain 
constituents of the cell walls, neglecting others, with the result that 
these walls are broken down, the wood being thus greatly weakened 
and more or less destroyed. It is the breaking down of the wood and 
the change in its physical and chemical qualities that is termed decay. 
The degree of decay is determined by the energy of growth of the 
fungus, “the length of time it has been at work, and the type of wood 
it attacks. Some fungi attack many different kinds of wood, while 
others are limited in their choice. Owing to their less exacting moist- 
ure requirements, wood-destroying fungi are able to live on heartwood 
as well as sapwood. The fruiting bodies, usually quite large, are 
found on the surface in the form of brackets, crusts, or mushrooms 
or toadstools. They are not developed until the hyphze have been 
at work for some time; consequently, the presence of fruiting bodies 
indicates serious decay. 
Two types of wood-destroying fungi may be recognized, (1) those 
mainly attacking the heartwood, rarely the sapwood, of standing 
living trees, and (2) those principally confining their activities to 
the manufactured product, such as sawed lumber, crossties, and. 
poles. The former type may continue their work of destruction after 
the tree has been cut down and worked up into lumber. The latter, 
attacking the manufactured product, usually invade the sapwood 
first, since it is far richer in stored food, generally has a higher 
moisture content than the heartwood, and is not so inherently re- 
sistant to decay. Fungi causing this type of decay are often very 
abundant in yards where the lumber is closely piled on damp earth, 
with little or no aeration under the piles, and much accumulated 
wood débris scattered throughout the yard. Unfortunately, such 
conditions are all too prevalent in mill yards. Sanitary yards both 
at the mills and the factories are badly needed. Humphrey (28) 
gives a complete account of the life history and habits of these fungi. 
the damage caused by them, and methods for their control. 
CONDITIONS AFFECTING DECAY. 
All conditions which favor sap stains are equally favorable to 
wood-destroying fungi. Furthermore, the latter can attack wood 
with a lower moisture content, so the fact that wood does not sap- — 
stain is no indication that fungi causing decay may not be present. 
The discolorations caused by the latter in sapwood are not so pro- 
nounced as sap- -stain; consequently, they are much harder to detect. 
Moisture in wood. —Dry lumber will not decay. The most efficient 
method to prevent decay is to air-dry or kiln-dry lumber immediately 
and then keep it dry by proper methods of storage. Placing dry 
lumber in the open, exposed to rain, or in damp sheds can not be too 
strongly condemned. If the lumber becomes moist again, it is just 
ie oe 
