﻿30 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 



The hyphse attack the cell walls very slightly, presumably living on 

 the tannin, of which oak wood contains a high percentage. The 

 value of the wood for veneers is very much enhanced. The writer 

 has no record of this discoloration being found on oaks in this 

 country. 



DECAY DISCOLORATIONS. 



The hyphse of wood-destroying fungi living 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 hyphse 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 debris 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. Humphrej' (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 



