Dec. 1, 1924 
Diagnosis of Decay in Wood 
545 
hole. The first reference to wall pene¬ 
tration by wood-rotting fungi is given 
by Willkomm (00), who made several 
excellent drawings showing the hyphae 
in the wood tissues but showed no 
definite penetration of the hyphae 
through the cell walls. R. Hartig {28, 
29, 80) was the first to demonstrate 
and illustrate correctly the penetration 
of cell walls by hyphae of wood-rotting 
fungi. Since Hartig’s time compara¬ 
tively little has been added to our 
knowledge of the subject. His work 
{28) shows that there are two principal 
methods of penetration exhibited by 
the various fungi studied. The (older) 
hyphae of the one group are always 
constricted when passing through the 
cell walls, while those of the other 
group show no constriction but pass 
freely through an opening in the cell wall 
as large or larger than the hyphal thread. 
Hartig illustrates the larger hyphae 
of Armillaria mellea {28, PL 11) greatly 
constricted, with the small, appa¬ 
rently young hyphae showing no con¬ 
striction. He shows the hyphae of 
Polyporus borealis markedly constricted 
{28, PL 10), with no enlargement near 
the host cell walls. But he figures the 
hyphae of Polyporus fulvus {28, PL 7) 
passing through the cell walls by way 
of large hourglass-shaped bore holes, 
and Trametes pini {28, PL 6), Poly¬ 
porus schweinitzii {28, PL 9), and 
Fomes igniarius {28, PL 16) passing 
through cell walls without constric¬ 
tion. A few bore holes are shown 
with no hyphae passing through in 
Stereum hirsutum {28, PL 18). ' For 
Fomes annosus {Trametes radiciperda) 
a few bore holes and one indistinct # 
penetration are noted {28, PL 4)- * 
No penetrations by hyphae are shown 
for Polyporus sulphureus {28, PL 14)* 
Lindroth {45) records the hyphae of 
Polyporus nigricans, Polyporus betu- 
linus, and Polyporus laevigatus boring 
without constriction through the cell 
walls. 
White (89) notes the constriction of 
hyphae of Fomes applanatus in in¬ 
fected wood. Hiley (35) records con¬ 
striction of hyphae for Dasyscypha 
calycina, Fomes annosus, and Poly¬ 
porus schweinitzii in larch wood. In 
the latter fungus the constriction is 
marked and in Armillaria mellea the 
hyphae are of the same size as the 
bore holes. These statements do not 
correspond with Hartig’s records as 
given above. 
Buller (14, fig . 1) illustrates the 
penetration of tracheid walls of pine 
by hyphae of Lentinus lepideus. No 
constriction is shown and the bore 
holes are larger than the hyphae. 
The mechanics of penetration through 
plant cell walls of hyphae of various 
fungi have always interested patholo¬ 
gists. There are several possible ways. 
Openings already provided may be 
used (36, 57, 7*2), or by means of 
enzymic action (3, 20, 26, 35, 42) an 
opening may be dissolved out of the 
wall. A third possibility is the forcing 
of an opening by mechanical means (31, 
32, 52, 55). Hawkins and Harvey 
(32) give a r6sume of the literature on 
penetration of plant cell walls and 
conclude that some good evidence sup¬ 
ports the view that certain parasites 
penetrate the hosts by mechanical means- 
Many wood-inhabiting fungi pass 
from one cell to another through such 
natural openings as the simple or 
bordered pits. It is of interest to 
note that the hyphae of wood-destroy¬ 
ing fungi as a rule do not seek these 
natural openings but pass through the 
cell walls at random, often passing 
through a large number of cell walls in 
a direct line, and often passing through 
the bordered pit very near its opening. 
In the case of wood-rotting fungi it 
would seem that the greater resistance 
offered by the thick, lignified walls of 
the tracheid and wood-fiber cells would 
preclude any possibility of a fungus 
hyphae forcing an opening by mechani¬ 
cal means only. The theory of enzyme 
action more nearly fits the facts 
observed. 
Size and shape of bore holes.— 
The bore holes by which the hyphae 
pass through the cell walls vary con¬ 
siderably with the stage of the rot and 
with the fungus in question. In cer¬ 
tain rots they are small in the incipient 
stage and become larger in diameter 
as the decay progresses (figs. 5 and 6). 
In such rots as those produced by 
Trametes pini, where the hyphae are 
constricted, very little change in the 
diameters of the bore holes is noted 
(fig. 5, B; fig. 6, 1 to 12). Those 
through which the very young hyphae 
pass are rarely smaller in diameter 
than those through which the older and 
larger hyphae extend. Where con¬ 
strictions occur in the hyphae when 
passing through the cell walls the bore 
holes are usually even, cylindrical, and 
perpendicular to the surface of the 
walls. This is brought out very well 
when the holes are seen in longitudinal 
section (fig. 5, Be and Fd). 
In other rots the section view shows 
the bore holes with irregular outlines, 
in many cases resembling roughly an 
hourglass. This feature is always 
found in connection with bore . holes 
which are usually twice to several 
times larger in diameter than the- 
