524 
Journal of Agricultural Research 
Vol XXIX, No. 11 
THE DIAGNOSIS OF DECAY 
If a piece of wood which shows 
plainly that it is decayed has attached 
to it the fruiting body of a wood- 
rotting fungus, a probable diagnosis 
can be made by identifying the sporo- 
phore; but, if the sample bears no such 
fruiting body and shows little or no 
surface signs of decay, determining the 
causal organism is much more difficult. 
The writer’s procedure is then as 
follows: First, the “unknown” is com¬ 
pared with a large number of 
“knowns.” This has been made pos¬ 
sible by the building up of a collection 
of some 600 or more typical rot speci¬ 
mens authenticated by the known 
identity of the sporophores collected 
on them. (Samples of wood rots col¬ 
lected from tree trunks which have 
lain on the ground for several years are 
not suitable on account of the possible 
presence of other wood-rot fungi in 
the same substratum.) These rots are 
grouped according to a classification 
presented below. 
The next step is a study of the gross 
characters of the rot and comparisons 
with descriptive data on various rots. 
It is obvious that a collection and 
detailed descriptions of rots are essen¬ 
tial in connection with studies of the 
gross characters. A key for the classifi¬ 
cation of wood rots will be the eventual 
outgrowth of these detailed descrip¬ 
tions. 
Details of hyphae and cell structure 
in the infected wood are then studied 
under the microscope and the cultural 
characters of the organism, isolated 
from the infected wood and grown on 
artificial media, are observed. These 
cultures and the subcultures obtained 
from them are next compared with 
authentic stock cultures. At this 
point the identification of the or¬ 
ganism can often be established with 
reasonable accuracy. A further test 
may be made to determine whether 
the fungus isolated from the unknown 
sample reproduces in sound sterilized 
wood an identical decay. 
THE STAGES OF DECAY 
Before the diagnosis can be dis¬ 
cussed in detail, it is necessary to define 
the terms decay, decay stages, decay 
processes, and the classification of 
decays. 
Decay (known to lumbermen as 
• ‘dote,” “doze,” or “punky wood”) is 
a process which begins with the 
development of wood-destroying fungi 
in wood and ends with more or less 
complete dissolution. The term in¬ 
cludes all stages in the destruction 
process and two principal stages have 
been recognized by writers on wood 
decay. The early development of 
decay has been termed: Beginning,, 
early, initial, incipient, advance, im¬ 
mature, first, primary, and invasion 
stage; and the final or decomposed 
stage: Final, last typical, advanced, 
mature, complete, ultimate, destruc¬ 
tion. The two descriptive terms, 
invasion stage and “ destruction stage,” 
were extensively used by Falck (22). 
The terms “incipient” and “typical” 
have been selected by the writer to 
represent the two stages. 
THE INCIPIENT STAGE 
The incipient stage of decay cor¬ 
responds to the period when the 
mycelium of the fungus is invading 
new host tissues preparatory to a more 
complete attack upon the cells (fig. 1,1). 
During this stage the hyphae ramify 
in all directions. In most decays the 
infected wood exhibits color changes 
although to the naked eye it appears 
to retain its structural characters, not 
having become punky, soft and spongy, 
stringy, ring-shaked or pitted. In some 
rots a softening of the wood may be 
detected in this stage and a character¬ 
istic brashness is evident, though with 
little or no discoloration. 
Incipient discolorations and zone 
lines (62, 63) usually accompany the 
incipient stage of decay. These are 
generally due to the presence of by¬ 
products resulting from the dissolution 
of the cell walls and cell contents by 
the fungous enzymes. 
THE TYPICAL STAGE 
The typical stage is that in which 
decay is plainly a factor in breaking 
down the wood cells. With few excep¬ 
tions it is accompanied by unmistakable 
changes in strength properties of the 
infected wood, changes in color and 
changes in continuity and texture (fig. 
1, T). One of the exceptions noted 
above is Trametes pini when the white 
pits are few and wide apart and the 
tissues are heavily infiltrated (16). 
Since infected wood undergoes color 
changes, the nature of the attacking 
fungus determines whether the rotted 
wood becomes whitish because of de- 
lignifying action, bleaching, or other 
causes, or whether the infected tissues 
become yellow, red, or brown due to a 
cellulose-dissolving action or to other 
causes not yet fully understood. The 
continuity of the wood tissues is broken 
in most decays in this stage. The wood 
