314 
cent germinability of conidia taken from 
mycelial mats during the 10-month period 
did not coincide with the time of highest 
concentration of conidia. ‘The best aver- 
age germination rate (39 per cent) was 
obtained from conidia that were collected 
in April, fig. 20. The next best germina- 
tion rate was obtained from conidia col- 
lected in November. A germination rate 
as high as 80 per cent was not uncommon. 
The number and germinability of conid- 
ia that were taken from mats of the same 
condition class did not vary unexpectedly 
from one study area to another, table 17. 
All areas included in the study were in the 
northern half of the state, and the dis- 
tance between any two areas was not 
greater than 165 miles. 
Pronounced differences were found, in 
the number and germinability of conidia, 
between the mats belonging to different 
condition classes, fig. 21. The highest 
average numbers of conidia were obtained 
from mature, or class II, mats. The high- 
est average per cent of germination oc- 
NUMBER OF CONIDIA 
(HUNDRED THOUSANDS) 
CLASSI CLASS II 
Intrinois NatrurAL History SurvEY BULLETIN 
CLASS IL 
Vol. 26, Art. 3 
curred in conidia from immature, or class 
I, mats. Both the number and germina- 
bility of spores changed as the condition 
of the mats advanced from class I toward 
class V or deterioration. 
The data dealing with number of co- 
nidia on a mat were based upon esti- 
mates of the average number of spores in 
1 ml. of suspension prepared from a 3-disk 
sampling of the mat. A rough approxi- 
mation of the number of conidia on an 
entire mat could be made by using figures 
obtained from the samples. The number 
of conidia in a mature mat which meas- 
ured 12 by 5 cm. with a central pad which 
measured 4 by 2 cm. was estimated as fol- 
lows. The average number of conidia 
from one disk of mat surface 7 mm. in 
diameter (383 sq. mm.) contained in 1 ml. 
of a 10-ml. water blank was 350,000 
spores or 3,500,000 spores from the entire 
disk. The area of the mat, after the area 
of the central pad (which had few or no 
spores) had been deducted, was 4,100 
square mm. The number of conidia on 
BB conioia 
[] GERMINATION 
PER CENT GERMINATION 
CLASS Iv CLASS © 
Fig. 21.—Average number and per cent germination of conidia of Endoconidiophora 
fagacearum taken from mycelial mats in five stages of development and decline over the 10- 
month period October, 1952, through July, 1953; class I, immature; class II, mature; class III, 
aging; class IV, declining; class V, deteriorating. 
