560 
Journal of Agricultural Research 
Vol. XXIX, No. 11 
DISCUSSION 
The methods employed in diagnosing 
decay in wood have been presented 
with sufficient detail to show that many 
of the questions on wood decay asked 
by both scientist and lumberman can 
be accurately answered. Proving that 
decay is present or absent, and that the 
causal organism is alive or dead, and 
whether the fungus is a wood destroyer 
or a staining organism, is relatively 
easy in a majority of cases. This has 
been demonstrated by the diagnosis of 
over 1,500 samples sent to the labora¬ 
tory for examination during two years. 
Gross, microsopical, and cultural char¬ 
acters were used in most of the diag¬ 
noses. A study of the microsocopical 
characters is made easier by a collection 
of microscopical mounts showing the 
characters of normal sound wood of 
various species. A similar collection of 
wood decayed by known fungi can be 
used to advantage in comparisons 
made with sections cut from the 
unidentified sample. A collection of 
stock pure cultures of the numerous 
fungi producing decay in wood is 
indispensible to the successful appli¬ 
cation of the cultural methods of 
diagnosis. The way in which cultural 
characters may furnish the evidence 
necessary to establish identity of the 
causal fungus, in addition to macro- 
scopical and microscopical data, is well 
illustrated by the following examples: 
A piece of heartwood oak showing a 
dark reddish-brown color was sub¬ 
mitted for diagnosis. The rot was in 
the late incipient stage and the gross 
characters placed it among the brown 
cubical rots. Microscopical examina¬ 
tion showed numerous signs of decay. 
Clamp connections observed on the 
hyphae developing in the wood indi¬ 
cated that the fungus was a Hyme- 
nomycete. Cultures were made and 
in a few days mycelium of a bright 
orange yellow appeared. This was 
compared with stock pure cultures, and 
it seemed reasonable to name the causal 
organism Polyporus sulphureus. 
A more positive case was a piece of 
white fir (Abies concolor ) plank show¬ 
ing a characteristic rot resembling that 
caused by Pholiota adiposa. Cultures 
on malt agar developed typical though 
small sporophores of this fungus. In a 
third case the cultures showed nearly 
perfect sporophores of Schizophyllum 
commune obtained on malt agar from 
fragments of infected wood taken from 
a birch log, and in a fourth case the 
cultures obtained produced abortive 
and typical sporophores of Lentinus 
lepideus when fragments of infected 
railroad ties were used. 
The close resemblance of the typical 
stage of the rots produced by such 
fungi as Trametes pint, Polyporus 
anceps, Fomes annosus, Stereum sul¬ 
catum, Stereum sanguinolentum , Tram¬ 
etes isabellina, Fomes nigrolimitatus f 
and Polyporus circinatus in conifers 
makes it difficult to determine the 
causal organism in the absence of 
sporophores. Cultures aid greatly in 
this diagnosis and only in the case of 
Trametes pini and Polyporus circinatus 
is there any very close resemblance of 
cultural characters. In this case care¬ 
ful comparisons will show sufficient 
differences to distinguish between the 
two. The cultures of Polyporus cir¬ 
cinatus on malt agar are a much darker 
brown than those of Trametes pini on 
the same medium. Other distinguish¬ 
ing characters such as rate of growth, 
type of surface growth, and discolora¬ 
tion of the medium are to be noted. 
Incidentally, the study brings out rath¬ 
er clearly the value of rot characters and 
cultural evidence in connection with the 
identification of dubious sporophores of 
fungi found with the typical rots. The 
following case is a good example: 
Diagnosis was attempted on a 
section of southern yellow pine fence 
post with several sporophores of a 
white polypore attached. The sap- 
wood and part of the heartwood 
showed large areas of a brown cubical 
rot. The cultures obtained from the 
brown rot areas indicated a species of 
Lenzites (PI. 10, D), but the sporophores 
attached showed a white context. 
Trametes serialis was suggested, since 
it produces a brown cubical rot. 
However, upon closer examination 
the early typical stage of a white 
pocket rot was observed in the sap- 
wood in proximity to the sporo¬ 
phores and merging into the brown rot. 
The white rot resembled that produced 
by Polyporus anceps . Cultures from 
the white rot areas, from the sporo- 
phore tissue, and from the spores cast 
by the near-typical sporophore devel¬ 
oped on malt agar in the cultures ob¬ 
tained from the brown rot areas fur¬ 
nished sufficient data to identify the 
sporophore as that of Polyporus anceps 
(PL 10, A and B). Sporophores of 
Lenzites trabea were later collected 
from another part of the same post. 
These were associated with a brown 
cubical rot. Cultures of the .sporo¬ 
phore tissue were identical with the 
Lenzites-like cultures obtained as above 
from the brown rot, and with cultures 
from the spores cast by the near¬ 
typical sporophores developed on malt 
agar (PI. 10, D). Therefore in this 
instance two fungi were isolated and 
identified from the same sample. 
