Dec. 1, 1924 
Diagnosis of Decay in Wood 
531 
orations as well as the typical charac¬ 
ters resemble each other closely. 
Zone lines. —Thin zones of dis¬ 
colored matter usually appearing in 
cross section as narrow to broad lines, 
particularly those associated with in¬ 
cipient decay, are valuable diagnostic 
characters (PL 4), though additional 
evidence is usually necessary. They 
are usually formed in the white rots 
only, being rare in brown rots. Their 
cause is still unsettled. Rhoads {62) 
concludes that the brown substance 
(decomposition products) commonly 
occurring in dicotyledonous woods 
attacked by wood-destroying fungi 
arises only after the death of the cells 
through the oxidation of their contents 
and certain constituents of their walls, 
occurring most notably in the 
parenchyma cells. 
Observations on zone lines formed 
between two fungi occupying the same 
wood tissues indicate that this type of 
zone line is fairly common, But in 
several cases these zone lines differed 
from the clear-cut, brightly colored, 
narrow lines formed through desicca¬ 
tion, which will be discussed later. The 
zone lines between the rots produced 
by Polyporus anceps and Lenzites 
sepiaria in. Picea canadensis , for ex¬ 
ample, are broader, up to one-fortieth 
inch wide, with indistinct edges and 
of a dull brownish color. Very often 
a double zone line is formed. The 
zope lines between rots of Fomes 
applanatus and Stereum frustulosum in 
Quercus sp. resemble the above closely, 
but are fainter and, less distinct. The 
zone lines of Fomes applanatus are 
usually narrow, brownish black to 
bl^ck, sharply defined, and rarely 
doubled. 
Schrenk {73) mentions the orange- 
colored zone lines accompanying the 
decay produced by Polyporus adustus 
in the sapwood of red gum {Liquid- 
ambar styraciftud ). The zone lines 
produced in wood inoculated with pure 
cultures of a fungus (Table I) isolated 
from sap-gum boards showing a white 
rot with orange zone lines, and pro¬ 
duced in pure cultures on malt agar 
are identical in width and color with 
those found in infected sap-gum lumber. 
However, the typical rot produced in 
this experiment is a white spongy rot 
and in the writer’s experience the 
typical rot of Polyporus adustus in 
certain broadleaf hosts is always a 
white mottled rot and is very charac¬ 
teristic. Whenever the white mottled 
rot was observed in connection with 
sporophores of Polyporus adustus, the 
orange zone lines were lacking. This 
would indicate that some fungus other 
than Polyporus adustus may be re¬ 
sponsible for the white spongy rot and 
orange zone lines in sap gum. 
Some writers {84, 89) attribute the 
zone lines in infected wood to reactions 
between two wood-inhabiting fungi oc¬ 
cupying the same substratum. White 
{89) in his description of the rot pro¬ 
duced by Fomes applanatus states 
that— 
black lines are encountered but cultural or other 
evidence shows that when they do occur more than 
one species of fungus is at work. They are produced 
at the point of contact of two invading fungi. * * * 
If this proves generally true, another 
type of zone line undoubtedly not 
caused by contact of two invading 
fungi must be accounted for. A study 
of the characteristics of a large number 
of wood rots shows that many of them 
have zone lines included within the 
typical rot areas (PI. 4). Although 
such areas, including zone lines, were 
cultured repeatedly, no fungus other 
than the one responsible for the decay 
developed in any case. Field observa¬ 
tions indicate that these zone finds oc¬ 
cur more commonly in the pieces of in¬ 
fected wood most subject to desicca¬ 
tion. Hartig {28, p. 32-39) states 
that the zone fines in oak wood infected 
with Fomes igniarius {PL 15, fig. 2) are 
due primarily to the entrance of air 
into the infected wood tissues. Lin- 
droth {45) figures a zone fine formation 
just back of the freshly-cut surfaces of 
birch wood infected with Polyporus ni¬ 
gricans. 
Additional observations, given in 
Table I, were made on large pieces of 
- infected wood brought in fresh from the 
woods. The pieces when cut at the 
time of collecting were in most cases 
completely infected but showed no zone 
lines; when cut open after a period of 
drying in the warm air of the labora¬ 
tory, many of the rots showed typical 
zone lines extending transversely across 
and but a short distance back from the 
ends of the infected log sections. Des¬ 
iccation and oxidation of the decom¬ 
position by-products seem responsible 
for the formation of these lines. Data 
EXPLANATORY LEGEND FOR PLATE 2 
Three typical brown rots (about natural size). A.—Brown pocket rot caused by Polyporus amarus in 
Libocedrus decurrens. “ Pecky ” incense cedar (radial section). B.—Brown cubical rot caused by Fomes 
pinicola in Tsuga canadensis. Note the white mycelial mats in the cracks. Radial section. C.—Brown 
spongy rot caused by Polyporus berkeleyi in Quercus alba. “ String and ray rot." The rays are left intact 
and form a remarkable contrast to the crumbly, spongy condition of the adjoining tissue. Radial section. 
7581—25t-2 
