Dec. 1, 1924 
Diagnosis of Decay in Word 
549 
hyphae which pass through them (16, 
17, 18, 19, in fig. 6). The hourglass 
shape appears to be caused by the 
greater resistance of the middle lamella 
to the decomposition process (19b, 
fig. 6). In a few cases hyphae were 
noted passing through bore holes of 
the same diameter as the hyphae. 
This is often observed where young 
hyphae are penetrating the walls (8, 
9, 10, in fig. 6). The hyphae pierce 
any part of the cell wall, often the 
curved or embossed part, or the mem¬ 
brane of the bordered pit; occasionally 
they pass through the pit openings 
(fig. 5, Bf and E). 
Hiley {35) in discussing the hyphae 
in larch wood infected with Fomes 
annosus states that—- 
to make these bore holes, the hyphal tips must 
excrete the necessary enzymes (presumably a lignase 
and a cytase). When once a hypha has gained 
passage from one tracheid to the next, the hole which 
it occupies ceases to enlarge, and it may reasonably 
be deduced from this that the enzymes are only se¬ 
creted by the apices of the hyphae. 
Observations on a number of fungi 
causing wood rot, and careful com¬ 
parison of the very young hyphae 
with the older ones which showed 
constrictions, indicated that the bore 
holes were usually as large or only 
slightly larger in diameter than the 
diameter of the young hyphae found 
penetrating the cell walls. The rela¬ 
tive size of bore holes in the tracheid 
cell walls in Pinus strobus infected 
with Trametes pini and of the hyphae 
producing them is shown in 1 to 10 of 
Figure 6. The bore hole produced by 
the largest hypha (fig. 6, 1) is little 
different in size from that produced by 
a very young hypha (fig. 6, 10), ex¬ 
hibiting no pronounced constriction. 
In (fig. 6, 11) is shown what might be 
taken for the early stage of penetration 
of a hypha, which is interpreted as the 
effect produced by sectioning obliquely 
through the hypha and the bore hole. 
Numerous hyaline hyphae smaller 
than those shown in 9 and 10 of Figure 
6 were noted in the tracheids, but they 
were not observed penetrating the 
walls. Some idea of the number of 
bore holes in the infected tissues may 
be gained by the photomicrograph in 
Plate 7 showing Trametes pini in 
southern yellow pine. Apparently, the 
young hyphae can only dissolve the 
cell wall, and beyond a certain point 
are incapable of enlarging the bore 
holes. The hyphae continue to grow 
in diameter and the characteristic 
constrictions are produced where the 
hyphae pass through the bore holes 
in the cell walls. All the evidence 
appears to confirm Hilev’s observations 
on Fomes annosus. 
Absence of hyphae in certain 
stages. —Very often when prepared 
sections, particularly those cut from 
the typical stage of a brown rot, are ex¬ 
amined under the microscope, numerous 
bore holes and other evidence of fungus 
action appear but hyphae are absent. 
It is not clear whether absence of hy¬ 
phae is due to loss during the handling 
of sections, or to resorption of the old 
hyphae, or, in the case of incipient 
stages of rot, to the invisibility of very 
fine threads (PI. 5) {43)- 
Buffer {11, 14) states that in wood 
decayed by Lentinus lepideus the hyphae 
often disappear, leaving but a trace of 
their former existence in the form of 
hyphaelike deposits of calcium oxalate 
crystals. 
Rhoads {63) finds scanty mycelium 
in the typical stage of rot produced by 
Polystictus pargamenus, and notes this 
peculiarity in other rots. He suggests 
that the enzymes produced by the fun¬ 
gus dissolve the older hyphae. 
Kauffman and Kerber {43), working 
with the rot produced in black locust 
by Trametes robiniophila, had difficulty 
in finding hyphae of the fungus in the 
older stages of decay, though bore holes 
and other signs of fungus activity were 
evident. They find this a frequent 
phenomenon in the typical stages of rot 
caused by some of the common wood- 
destroying fungi. 
Since bore holes vary for different 
rots (see above, p. 545), and certain in¬ 
fected woods exhibit bore holes consid¬ 
erably larger than the hyphae which 
pass through, it is possible that in cut¬ 
ting microtome sections from such mate¬ 
rial without embedding in celloidin or 
paraffin the hyphae may become broken 
and may eventually become lost from 
the section. 
A summary of the main microscopical 
characters of diagnostic value assem¬ 
bled during this study is given in Table 
IV. In the absence of hyphae identifi¬ 
able as wood destroyers the bore holes 
are perhaps of prime importance. Spi¬ 
ral cracks and corrosion marks are re¬ 
liable when accompanied by hyphae, 
particularly when the hyphae show no 
characters such as buckles or medal¬ 
lions which can be used to class them as 
wood-rot fungi. In wood showing no 
distinctive gross or microscopical char¬ 
acters the proof that the hyphae ob¬ 
served belong to a wood-rot fungus 
rests entirely upon the success of cul¬ 
tural methods. (These observations 
may not hold for all species of wood and 
under all conditions. The number of 
species examined is limited, particularly 
for any given fungus, and the study 
should be continued to obtain further 
