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 the wood appear bleached. Black zone lines may develop in the light areas. Unless severely
degraded, the wood does not crack across the grain and does not collapse or shrink abnormally as
with the brown rots. A white fibrous mass may result.
The strength properties decrease gradually with the exception of toughness.
Soft rot (Figure 4-8) occurs when fungi create elongated, spindle-shaped
cavities which follow the angle of the cellulose fibril within the cell wall. Wood exposed to very
wet conditions seems to suffer most commonly.
The surface of wood that has soft rot can be scraped off with a fingernail. The wood is darkened,
dull brown to blue-gray. When dry the surface may appear as though it had been lightly charred,
and there will be profuse fine cracking and fissuring both with and across the grain. When probing
with a sharp object, the degraded wood will be comparatively shallow and the transition between it
and the underlying firm wood will be abrupt.
The soft rot fungi have been shown as a group to be able to better tolerate certain extremes of the en-
vironment such as higher temperatures, higher pH's, tolerance of preservative chemicals, and ability
to grow with restricted oxygen. They are important in cooling towers and in hardwoods preserv-
atively treated with water-borne preservatives.
4.2.3.2 In Trees. The term, "pocket rot", describes decay in wood that is charac-
terized by small cavities of severe decay, scattered throughout the wood. Two pocket rots which
started in trees growing in the forest and which are seen in wood after the products are put into ser-
vice are described below:
White pocket rot (Figure 4-9), in the advanced stage, appears as spindle
shaped, pointed pockets or cavities parallel to the grain and separated by apparently sound wood.
Within the pockets, the wood is reduced to a white fibrous mass of cellulose, and in other cases the
pockets may be empty. This type of decay may be seen in Douglas-fir lumber cut from old growth
trees. This lumber is accepted in certain grades.
Brown pocket rots (Figure 4-10) can affect softwood species such as cedar and
cypress. The pockets are elongated in the direction of the grain and are several tunes longer than
broad. In the early stages of decay, the pockets are at first firm, and in the advanced stages are filled
with a dark brown, carbonaceous, crumbly mass typical of brown cubical rot. The line of separation
between the sound and decayed wood is sharp.
The fungus may continue development in dead trees, but it does not develop after wood is placed in
service. Therefore, control measures are not necessary.
4-15
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