Nov. 3,1923 Five Molds and their Penetration into Wood 
22 5 
adhered to the wood and here and there dark areas were found on the 
sides of the blocks. 
The development of the mycelium within the blocks was especially 
marked and abundant in the case of this species of mold. The hyphae 
not only extended longitudinally, but frequently also bored transversely 
through even the thicker cell walls. In aspen and the oaks the mycelium 
of this fungus was found abundantly in the rays, fibers, and vertical 
parenchyma, as well as in the vessels (PI. 4). In the red oak particularly 
very fine hyphae, as well as coarse, vigorous ones were observed. In 
spruce the most abundant growth was near the surface, where very fine 
hyphae were produced, but the hyphae penetrated also to the very 
center of the block, traversing both the sap wood and the heartwood, a 
small amount of which was present in the test blocks. The tendency 
of the hyphae of this mold to bore through thick cell walls, especially in 
the aspen blocks, is clearly illustrated in Plate 4. Their penetration 
through the end walls of vertical parenchyma cells is shown in Plate 4, B. 
The attack of Penicillium divaricatum upon the wood cell walls was the 
most effective of any observed in the study. 
DISCUSSION AND CONCLUSIONS 
The test blocks were frequently much discolored and stained by the 
surface growth or spores of the molds or by water stain; but they were 
not appreciably softened, except in the case of Penicillium divaricatum 
on spruce, where the wood appeared unusually soft when sectioned with 
the microtome. 
The development of the mold mycelium in the test blocks as observed 
under the microscope was found to vary considerably. Some of the 
molds showed more penetration of the cell walls than others, although 
practically all were found well below the surface of the blocks. More¬ 
over, growth in the vessel cavities alone, such as was found in the case of 
red oak with Aspergillus sp. and Ceratostom'ella sp., presumably indicated 
less damage to the wood than would be expected in those cases where 
the hyphae were present in the rays and fibers, as was the case especially 
with Monilia sitophila and Penicillium divaricatum and also with other 
molds in white oak and aspen. 
It is apparent from the results here shown that Monilia sitophila and 
Penicillium divaricatum penetrated the cell walls of the wood to a greater 
extent than did the other molds. Observations on the behavior of 
Ceratostomella sp., a blue stain fungus, made by others (jo, 12) have given 
evidence that this mold can also penetrate the cell walls and cause their 
thinning to a greater extent than was observed in the present test, but it 
is nevertheless maintained by pathologists that this does not materially 
affect the strength of the wood for ordinary commercial purposes. 
It is apparent from the foregoing that the mycelium of certain molds 
may actually penetrate wood to a notable extent, even traversing thick 
cell walls (PI. 4, A, C, and D). In general, however, it was observed that 
the tendency was to follow the cell cavities, especially those of the vessels 
or tracheids near the surface and (PI. 2, B, C) to pass from cell to ce.ll 
through the thin areas offered by the pits. 
The effect of such an infection upon the strength of the wood has not 
been determined; but, until they are proved not guilty, it would appear 
that molds should be guarded against as much as possible in the endeavor 
to advance the cause of general lumber sanitation, and especially should 
molding be prevented in the case of material for exacting uses. 
