Culture of Verticillium olbo-atrum , B. et Br. 527 
sufficient moisture present no growth took place in 30° or 35 0 C. after seven, 
fourteen, or twenty-one days.’ 
The usual bacterial method was followed to determine the thermal 
death-point of the fungus. A number of tubes of melted potato-mush agar 
were inoculated and kept at 40° C. for ten minutes and then poured into 
sterile Petri dishes and cooled rapidly. Next the temperature of the bath 
was raised to 43 0 C., and another set of tubes inoculated and kept there for 
ten minutes, and then poured into sterile Petri dishes and cooled rapidly. 
Similar experiments were made at 46°, 49 0 , 52 0 , and 55 0 C. These Petri 
dishes were incubated at 22-5° C., the optimum temperature for this fungus. 
Innumerable colonies appeared on the second and third day from those ex¬ 
posed to 40°, 43 0 , and 46° C. A smaller number of colonies appeared at 
49 0 C. No colonies appeared at 52 0 C. Next a similar set of experiments 
were made at 48°, 50°, 52 0 , and 54 0 C. A number of colonies appeared at 
48° and some at 50° C. One or two colonies appeared in some cases at 52 0 
and none at all at 54° C. So the thermal death-point may be put between 
52 0 and 54 0 C. for a ten minutes exposure. 
Growth in Media of Different Concentration at One 
Temperature. 
It has been found that if certain amounts of food material are 
present the increase in diameter of the mycelium is fairly constant for 
a particular temperature, provided that the thickness of the medium is the 
same in all cultures. Thus a colony will spread equally in Coon’s normal, 
half normal, and quarter normal, if incubated at the same temperature. The 
following are the actual measurements (squares of the diameter in mm.) for 
Coon’s N/i, N/2, and N/4 at temperatures 2i° and 25 0 C. It will be seen 
from Fig. 5 that spread is equal for different concentrations at the same 
temperature. 
21° C. 25° C. 
Days . 
N/i 
N/2 
N/ 4 
Days. 
N/i 
N/2 
N/ 4 
4 
81 
IOO 
77 
4 
5 <J 
60 
68 
5 
182 
l88 
15° 
5 
90 
IOO 
106 
6 
361 
3 2 4 
3 2 4 
6 
150 
r 75 
182 
7 
5 2 9 
494 
461 
7 
225 
289 
270 
8 
702 
665 
575 
8 
330 
319 
410 
9 
930 
900 
870 
9 
475 
560 
560 
10 
1225 
ii 35 
1135 
10 
650 
729 
729 
11 
1560 
!444 
1482 
11 
860 
961 
990 
12 
1936 
1831 
1849 
12 
1089 
1190 
1190 
13 
2304 
2190 
2227 
13 
J 354 
1444 
1480 
14 
2601 
2 57 ° 
2650 
14 
1600 
I 74 ° 
1720 
15 
3° 2 5 
3 IO ° 
3080 
15 
1916 
2025 
19S0 
16 
348 1 
3457 
3600 
16 
2240 
2 3 2 5 
2 35 ° 
In one case, however, the effect of a difference of temperature was not 
manifest. This was with a six-months-old solution (Coon’s normal) in which 
growth had previously stopped ; the pH was 8*2. This medium was filtered, 
Mm2 
