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 (6,7). 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 hyphe may 
remain dormant, ready to continue their work of destruction again 
if suitable conditions arise. The chalky quinine fungus (Pomes 
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 hyphe and their spread 
to adjoining sound timbers. The rose-colored Fomes (/omes 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 hyphe. However, this does not 
prevent reinfection and subsequent damage if conditions for decay 
