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



it is usually completely resin soaked or contains pitch streaks which 

 make it unsuitable for painting or contact with fabric coverings. 



INCIPIENT DECAY. 



It is a simple matter to recognize well-advanced rot or typical 

 decay. Here the changes in the wood structure due to the longer 

 action of the wood-destroying fungus are so profound as to be very 

 plainly apparent, but the earlier stages of decay, termed incipient 

 decay, immature decay, or advance rot, are often far from easy to 

 detect (G, 7). In some cases detection is practically impossible with- 

 out a microscopical examination of the wood. 



Specific gravity is not a reliable index of decay. It has been sug- 

 gested that decay in any piece of wood will be immediately reflected 

 in a lowering of the specific gravity. But this can not be detected 

 unless the specific gravity of the piece was known before decay com- 

 menced, a manifest impossibility in most cases. Incipient decay does 

 not cause a sufficient reduction in the specific gravity to bring the 

 heavier pieces of wood below the minimum set for the species. The 

 writer has tested pieces of yellow birch, white ash, and Douglas fir 

 with conspicuous incipient decay and found the specific gravity of the 

 affected pieces to be from 0.05 to 0.2 higher than the minimum per- 

 missible. The same condition will exist in all species. Douglas fir 

 with pronounced white cellulose pockets characteristic of the final 

 stage of red-rot or conk-rot has been found in some cases to have a 

 higher specific gravity than the minimum of 0.45. Of course, when 

 sound such wood had a high specific gravity. 



Wood is weakened by incipient decay, the degree depending on the 

 stage of the decay and somewhat on the species of fungus at work. 

 Furthermore, if infected material is merely air dried the hyphae may 

 remain dormant, ready to continue their work of destruction again 

 if suitable conditions arise. The chalky quinine fungus (Fomes 

 laricis (Jacq.) Murr.), which normally causes decay in the heartwood 

 of various coniferous trees, either living or dead, has been found 

 causing decay in the roof timbers of cotton weave sheds (5). Un- 

 doubtedly this originated from timbers containing incipient decay 

 of this species placed in the roofs at the time they were built, where 

 the high temperature and humidity which prevails in such sheds soon 

 resulted in renewed activity of the fungous hyphae and their spread 

 to adjoining sound timbers. The rose-colored Fomes (Fomes roseus 

 (Alb. and Schw.) Cke.), which is common on dead trees and is some- 

 times found on living trees in the coniferous forests of the Pacific 

 Northwest, has been found to be very destructive to timbers in base- 

 ments with high humidity and poor ventilation in the Northeastern 

 States (26, p. 28). As a general rule, infected wood must not be 

 used. 



It is extremely doubtful whether incipient decay in one of the 

 laminations of ply wood can be considered an important defect. 

 In the first place, the reduction in strength would be negligible. 

 Furthermore, there would be but little danger of the fungus ever 

 resuming its activities, because the high degree of heat and humidity 

 to which the ply wood is subjected during various stages of its manu- 

 facture must kill the vegetating hyphae. However, this does not 

 prevent reinfection and subsequent damage if conditions for decay 



