Dec. 1, 1924 
Diagnosis of Decay in Wood 
535 
on the appearance of zone lines in wood 
inoculated with pure cultures of wood- 
destroying fungi support this view. 
The zone lines invariably appeared 
during the periods when the moisture 
in the tubes and in the inoculated 
blocks had nearly evaporated. Zone 
lines were secured in the following 
cultures on the hosts named: Trametes 
pini in Picea sitchensis heartwood, 
Fomes igniarius in Populus tremuloides 
sap wood, Xylaria polymorpha in Tilia 
americana heartwood, Polyporus adustus 
(?) in Populus tremuloides sap wood, 
Hymenochaete rubiginosa in Populus 
tremuloides heartwood, Fomes applana- 
tus in Populus tremuloides sapwood, 
Ganoderma curtisii in Populus tremu¬ 
loides sapwood and in pure cultures on 
malt agar, the mycelium extending to 
the cotton plug and forming a zone 
line across the plug. 
The data in Table I indicate that 
whenever freshly cut pieces of wood in¬ 
fected with certain fungi are placed in 
a dry room or left to dry in the open, 
characteristic zone lines are formed a 
short distance back and parallel to the 
cut surfaces (PI. 4, A, B, C). Field ob¬ 
servations often show zone lines in the 
upper portion of rotted stumps in the 
region where excessive drying occurred, 
roughly parallel to the surfaces from 
which the evaporation took place. 
Zone lines may be regarded as addi¬ 
tional evidence or as aids in diagnosing 
decay, but in most cases can not be 
regarded as infallible characters in de¬ 
termining the causal organism. The 
data indicate that one type of zone line 
is commonly formed during desiccation. 
Other types, less common, have various 
origins. The entire problem of zone 
lines needs to be attacked from the 
microchemical angle in order to de¬ 
termine the fundamental causes for 
these characteristic despoits. In this 
way their diagnostic value may be 
more fully developed. 
Texture. —Texture may be de¬ 
termined by hardness, elasticity, brash¬ 
ness, or ease of crushing or crumbling. 
Hardness may be tested in a number of 
ways, but the comparative resistance 
offered when a knife blade or a dull 
point is jabbed into sound and decayed 
wood has been found fairly satisfactory. 
Prying up slivers of the wood with a 
knife blade often furnishes comparative 
evidence. This common test for elas¬ 
ticity in general use by inspectors (7) is 
of value since the sounder wood pulls 
out with a more splintery appearance 
and shows greater elasticity and coher¬ 
ence than the infected wood. The 
manner in which fibers tear out at the 
saw cuts is also a reliable sign of decay. 
Brashness. —The tendency to break 
without a splintering fracture is often 
an indication of decay. Out of several 
thousand specimens of Sitka spruce 
tested at the Forest Products" Labora¬ 
tory for their mechanical strength 
properties, 16 were selected as repre¬ 
senting the splintering or tough type of 
failure and 15 as representing the brash 
or weak type. The section of wood 
technology of the Forest Products 
Laboratory made a careful study of the 
wood structures of each piece and found 
no definite physical cause for brashness. 
Later the writer found minute hyphae 
of a wood-destroying fungus in nearly 
all of the 31 brash sticks (PL 5). Only 
one of them showed faint rot discolora¬ 
tions, the remainder appearing normal. 
Two of the tough sticks contained 
blue-stained sapwood and the third 
contained only a very few hyphae of 
the wood-destroying type of fungus. 
Brashness may, of course, be due to 
other factors also. 
Odor. —Polyporus schweinitzii rot in 
Sitka Spruce has a noticeable anise-oil 
odor, and Polyporus berkeleyi rot in oak 
also has a peculiar odor of anise oil. 
A turpentine odor accompanies the 
typical stage in most conifers. A 
somewhat similar odor accompanies the 
rots caused by Lentinus lepideus Fr. 
and by Polyporus fissilis. 
Chromo - chemical tests. — These 
are the gross color reactions produced 
by the application of chemicals to the 
surface of the decayed wood. These 
chemicals are principally so-called lig¬ 
nin or cellulose indicators, and accord¬ 
ing to Crocker (18) the aldehydes 
usually present with lignin compounds 
are responsible for the specific color 
reactions. 
MICROSCOPICAL CHARACTERS OF 
DECAY 
The hyphae present in infected wood 
are usually of two kinds, the older, of 
large size, sometimes colored and 
usually much branched or anasto¬ 
mosed; the younger, very small, hya¬ 
line, and irregularly branched. Often 
these young hyaline hyphae are very 
difficult to detect even with the aid of 
suitable stains and oil immersion 
lenses (Pl. 5). With the exception of 
the hyphae of some of the sap-stain 
fungi, the hyphae found boring through 
the cell walls are rot producers. 
Hyphae may be found in the medullary 
rays, in tracheids, in vessels, in sap- 
wood or in heartwood, and may be 
colored or hyaline. Clamp connections 
sometimes called buckles or nodose 
septae usually indicate a wood de- 
