846 
Journal of Agricultural Research 
Vol. XXIII, No. II 
of the resulting colonies from day to day. The best comparative data 
were obtained when the cultures were 4 to 6 days old. 
A sparse, slow growth occurred at 3 0 to 4°C., a light growth developed 
at 5 0 , and an appreciable amount of mycelium developed at 8° after an 
interval of 10 to 12 days. Above this temperature, the rate of growth 
increased rapidly, the optimum falling at 24 0 with unacidified agar, 
and at 28° with acidified agar. Little or no growth occurred above 32 0 
to 34 0 , regardless of the time incubated. The average diameters of the 
colonies are given in Table III and shown graphically in figure 4. The 
diameter and texture of the colonies of a single series are shown in 
Plate 3, C. 
Table III—Influence of temperature on the vegetative development of Gibherella sau- 
binetii incubated on potato-dextrose agar 
Reaction of medium and 
Aver¬ 
age 
num¬ 
Age of 
culture 
(days). 
Average diameter of colonies in centimeters at 
different temperatures. 
inoculum. 
ber 
deter¬ 
mined. 
8° C. 
ia # C. 
i6°C. 
20° C. 
24* c. 
28° C. 
3 2°C. 
36* C. 
Unacidified agar, conidia. 
8 
4 
O. I 
1-3 
2 . 5 
5-9 
8 . 1 
7- 5 
o *3 
0 
Acidified agar, conidia.. 
8 
4 
O 
• 7 
1 . 7 
3 . 0 
3- 1 
5- 7 
. 1 
0 
Unacidified agar, myce¬ 
lium.. 
8 
4 
1 . 5 
2 . 5 
4- 5 
6.5 
9 . 0 
7-3 
1 . 6 
. I 
Acidified agar,mycelium. 
9 
4 
•7 
1.4 
*•3 
2.7 
4.5 
6. 0 
x * 3 
0 
The cardinal temperatures for mycelial growth were about the same 
when the fungus was incubated on the stems of young wheat seedlings 
growing in tubes of sterile soil, the optimum rate of growth ranging from 
24 0 to 28° C. No mycelium was found on the seedlings at temperatures 
above 32 0 to 34 0 C. 
PRODUCTION OP CONIDIA 
Observations on the production of conidia by the fungus were made on 
potato-dextrose agar poured plates, in hanging drops of potato-dextrose 
agar, and on the stems of young wheat seedlings growing in tubes of 
sterile soil. Conidia were produced at temperatures ranging from 4 0 to 
34 0 C., as shown in Table IV. 
Table IV .—Influence of temperature on the production of conidia by Gibberella saubinetii 
in hanging drops of potato-dextrose agar 
24 hours. 
2 days... 
3 days... 
4 days... 
6 days... 
9 days/.. 
18 days. 
Rate of production and comparative number of conidia produced 
at different temperatures. 
Time incubated. 
4 * C. 
O 
o 
o 
o 
o 
o 
o 
11° c. 
17 0 C. 
24° C. 
28° C. 
30° C. 
3 a°c. 
34 ° c. 
0 
0 
I 
° 3 g 
log 
log 
0 
0 
3 
iog 
log 
log 
log 
2 
0 
iog 
xog 
log 
log 
log 
3 
I 
log 
log 
log 
log 
XOg 
4 
10 
log 
xog 
log 
log 
*0g 
log 
4 
• Letter g following a number indicates new conidia germinated after being produced. 
