300 
came progressively narrower higher up, 
in others it appeared first at the top of the 
bole and progressed downward, and in 
still others it started at top and base at 
the same time. In some trees, the brown- 
ing of the wood occurred in a spiral man- 
ner on the bole; with time the brown strip 
became gradually wider and was followed 
by loosening of the bark. Two to 5 weeks 
later the strong characteristic odor of the 
fungus could be detected. Usually at this 
stage, mycelial mats formed in a few days 
if weather conditions were favorable. 
Several days prior to mat formation, a 
uniform, very sparse, barely visible my- 
celial growth was seen on the surface of 
some of the odoriferous wood. When 
pieces of this wood were removed and kept 
moist at 12 degrees, pure cultures of En- 
doconidiophora fagacearum appeared in 3 
days. Frequently the first mats to form 
on a tree followed the decline of the tree 
so closely that the mats extended from 
the brown wood under loose bark to the 
adjacent green wood under tight bark. 
In some trees, mats appeared first at 
the base of the trunk, but, in many trees, 
they appeared first at the top of the trunk 
or on some of the large branches. How- 
ever, as the top part of the tree declined 
more rapidly than the lower part, and 
soon became dry, in most trees a larger 
number of mats formed on the lower half 
of the bole. The distances at which 355 
mats were located above the ground on 
different trees in all areas were estimated. 
Of this number, 3 mats were found be- 
tween 6 inches and 1 foot above the 
ground, 111 were located between 1 foot 
and 10 feet, 133 between 10 and 20 feet, 
64 between 20 and 30 feet, 33 between 30 
and 40 feet, and 11 at heights of 40 to 50 
feet. 
The areas of loose bark on a tree could 
be traced accurately by following the dull 
sound given off when the trunk was 
tapped lightly with a blunt instrument. 
Where mats were present the dull sound 
was pronounced, and close examination 
revealed small cracks in the crevices of 
the bark. However, not all cracks that 
appeared in the bark of wilt-killed oaks 
were the result of mycelial mat or pad 
growth. Occasionally very small cracks 
were found, beneath which the odor of 
the fungus was strong but where no mats 
Intinors NATURAL History SurvEY BULLETIN 
Vol. 26, Art. 3 
or pads were visible. When the bark of 
these places was lifted, replaced immedi- 
ately, and nailed down securely, abundant 
mycelial growth of Endoconidiophora 
fagacearum developed within 2 weeks. 
This experience indicated that cracks may 
precede mat formation. By the time the 
pressure created by mats growing beneath 
the bark is strong enough to crack the 
bark at crevices, the bark has been con- 
siderably weakened. During a period of 
rapid growth in the spring, many pads 
pushed the bark out so far that small 
pieces of the bark were dislodged, leav- 
ing portions of the pads exposed to the 
outside. The sizes of cracks in the bark 
seemed to vary according to the sizes of 
the mats beneath. In some instances, the 
combined effects of two mats, one below 
the other, caused very long cracks to form. 
The longest crack of this type found meas- 
ured 3 feet. 
The trunks of trees examined in the 
mat-producing stage did not always have 
the fungus odor distributed uniformly 
over the wood. In most trees in this stage, 
the odor occurred in small, scattered areas 
along the bole, the wood between these 
areas having none of the odor. When pieces 
of wood cut from areas with strong odor 
were placed in a moist chamber at 16 
degrees, abundant mycelial growth of the 
oak wilt fungus appeared in 3 to 5 days. 
Wood that was taken from adjacent areas 
without odor did not produce any visible 
growth when treated in this manner. 
Mats normally formed on the wood 
surface or on the surface of the inner bark 
of trees, but several mats were found 
which had developed entirely within the 
inner bark. These were typical mats with 
central pads, the largest measuring 18 by 
6 cm. 
Mats on Felled Trees. 
Five wilt-killed trees selected for study 
of the development of mycelial mats on 
cut timber were felled at different times 
of the year. Tree H-4 (Havana area) 
was felled on September 23, 1952; tree 
P-6 (Peoria area) on October 21, 1952; 
tree R-8 (Rockford area) on November 
3, 1952; tree R-7 on December 16, 1952; 
and tree R-6 on May 5, 1953. Trees H-4 
and P-6 were felled in an early stage of 
