320 
medium was favored by temperatures of 
16 and of 25 degrees C. 
Tests in vitro showed that longevity of 
conidia of Endoconidiophora fagacearum 
was favored by low temperatures and a 
dry atmosphere. Under conditions of high 
humidity, conidia on artificially grown 
mats remained viable for 102 days at 0 
and at 12 degrees C. Under conditions of 
low humidity, conidia on similar mats 
were still viable after 250 days at 0, at 
12, and at 16 degrees. Conidia on a mat 
taken from nature and subjected to dry 
storage at 16 degrees were still viable 
after 330 days. 
Laboratory feeding tests revealed that 
insects of the family Nitidulidae were ef- 
fective destroyers of mats of the oak wilt 
fungus. 
The rate at which wilt-infected oaks 
declined and the length of time required 
for trees to reach a condition favorable 
for the development of mycelial mats 
were found to be closely related to the 
time of incipient wilt. 
The influence of monthly temperature 
and precipitation on formation of mats of 
the oak wilt fungus was suggested by ac- 
celerated mat development during April, 
May, and June. The average tempera- 
tures for May and June were near the 
optimum temperature for growth of the 
fungus. 
The development of macroscopic my- 
celial growth of Endoconidiophora faga- 
cearum was readily induced during 
March, April, and May simply by mak- 
ing cuts through the bark of trees that 
were nearing the mat-producing stage. 
This experience suggests a strong air re- 
lationship in mat formation. 
In March and April, padless mats of 
the oak wilt fungus formed and grew on 
17 of 213 pieces of bark that were taken 
from diseased oaks and placed on the for- 
est floor. No macroscopic growth formed 
on any of 128 wood pieces that were 
treated in the same manner. 
The time required for fungus mats on 
trees to progress from an immature stage 
to a deteriorated condition varied accord- 
ing to the season in which the mats first 
appeared. Mats that first appeared dur- 
ing the spring and summer declined rap- 
idly as compared with mats that first ap- 
peared during the autumn and winter. 
Intinors NATURAL History SurvEY BULLETIN 
Vol. 26, Art. 3 
Insect activity on mats in nature was 
greatest during April, May, and June, 
when more species of insects were found 
than in other months. Members of the 
families Nitidulidae, Staphylinidae, and 
Histeridae, and of the order Collembola 
were more abundant than others. Among 
other agents commonly associated with 
mycelial mats were nematodes, mites, bac- 
teria, fungi of various kinds, and crusta- 
ceans. 
A total of 649 typical mycelial mats, 
each with a pad in the center, were found 
on 31 selected trees, some of the mats in 
each month of the 10-month study period. 
Spore counts from mat samples indicated 
that the highest concentration of conidia 
on mats was reached in December, after 
which there was a steady decrease during 
a period of low winter and spring tem- 
peratures until April, when a sharp rise 
occurred with the rise in temperature. 
After April the number of conidia de- 
creased rapidly until, in July, no conidia 
could be found on mats. In the laboratory, 
best germination was obtained from conid- 
ia that were collected in April and good 
germination from those collected in Octo- 
ber, November, and March. The highest 
average number of conidia was obtained 
from mature mats but the highest ger- 
mination rate of conidia was obtained 
from immature mats. 
The significance of mat size, as well 
as numbers of mats, in accounting for the 
concentration of conidia in an oak wilt 
area was demonstrated from sample data. 
A mat that measured 24 by 10 cm. was 
estimated to contain 1,650,000,000 co- 
nidia. 
Twenty-three per cent of 393 mats 
(which were presumed to be old enough 
to have perithecia) contained perithecia. 
Mats with perithecia were found in all 
months of the study except July, and the 
highest average number of perithecia per 
mat sample was found on aging mats in 
May. The best germination rate was ob- 
tained with ascospores collected from ag- 
ing mats in April. 
Mass transfers of cells from the inte- 
rior portions of 423 mycelial pads to po- 
tato dextrose agar showed that cells from 
immature, mature, and aging mats were 
viable; 82 per cent of the pads from im- 
mature mats gave positive cultures. 
r 
