Dec. 1, 1924 
Diagnosis of Decay in Wood 
543 
The presence of hyphae in the vari¬ 
ous areas in infected wood was deter¬ 
mined by microscopical examination of 
radial and transverse sections specially 
stained for this purpose (figs. 3 and 4). 
The Bismarck brown-methyl violet 
method of staining (38) was used in the 
majority of cases. Plate 5 shows a 
radial section of Picea sitchensis con¬ 
taining minute hyaline hyphae of a 
wood destroyer, Polyporus schwenitzii, 
stained by the above method. The 
minute hyphae could not be observed in 
the wood cells before staining. The 
piece of wood from which this section 
was cut showed no discolorations to in- 
infected with Fomes laricis and Fomes 
pinicola. The incipient decay pro¬ 
duced in firs and hemlocks by the 
Indian paint fungus, Echinodontium 
tinctorium, is known to continue 
longitudinally about 4 to 6 feet ahead 
of the discolored areas. Microscopical 
examination discloses hyphae some 
distance radially from the faintest 
discolorations (fig. 4, B). 
Microscopical evidence therefore in¬ 
dicates that in certain rots the hyphae 
advance as far as the edge of discolor¬ 
ation; and that in other rots, principally 
those of the brown rot group, the 
hyphae may be found a considerable 
Fig. 4.—A.—Section of Tilia americana infected with Pholiota adiposa. a, incipient area; b, invasion zone; 
c, sound area. Sections for examination were taken from areas 1 to 10. Failure to find hyphae in 6 may 
have been due to the minuteness of the threads. No hyphae were observed in 7 to 10. Cultures made by 
using fragments from the invasion zone usually give positive results. B.—Section of fallen trunk of 
Tsuga heterophylla infected with Echinodontium tinctorium. Typical rot at a showing characteristic 
reddish streaks. Incipient rot at b with extremely faint discoloration at c. Apparently sound sapwood 
region at d. Hyphae were observed in all of sections 1 to 6. Apparently the fungus invaded the sap- 
wood after the tree died. C.—Section of pulp log of Picea canadensis infected with Lenzites sepiaria. 
Typical rot in shaded areas. Very faint discoloration immediately surrounding the typical rot. Region 
near 2 and 3 apparently sound. Hyphae were observed in all the sections cut for examination. The 
distance from edge of typical rot to outer edge of 3 is 2 y$ inches. 
dicate the presence of a wood-destroy¬ 
ing fungus. 
Hyphae were noted in the apparently 
sound wood of Pinus banksiana in¬ 
fected with what appeared to be 
Fomes roseus. On close observation 
this area showed a very faint greenish 
color on the outer edges and a pale 
yellowish-brown color between this 
and the typical rot area. 
Hyphae are present some distance 
beyond the discolored areas in wood 
distance beyond the faint discolored 
areas in the incipient rot region. 
Cultural experiments. —Frag¬ 
ments of infected wood were removed 
at regular intervals from the typical 
stages of rot, through the incipient 
stages and from the apparently sound 
wood beyond. 3 In the late typical 
stage of most of the brown rots it was 
very difficult to obtain cultures un- 
contaminated by molds. Apparently 
the shrinkage in this stage of decay 
3 The technique employed was essentially thatdescribed in V. S. Dept. Agr. Bui. 1262 : 40. 
