THE CONTROL OF CABBAGE BLACK-LEG. 9 
may serve as sources of subterranean infection of near-by seedlings. 
Treatments with solutions heated to 55° and 60° C. for the very 
short periods of 1 to 5 minutes were so injurious that their effect upon 
infected seeds was not given further consideration. It was thus very 
evident that complete disinfection of infected seeds with a formalde- 
hyde solution is impossible without material injury to the subsequent 
development of the plants. Moreover, the fact that protracted treat- 
ment with this fungicide results in very serious injury to the host 
plant precludes its use even in those special cases where complete 
eradication of the parasite is so much desired that moderate seedling 
injury would be tolerated. 
HOT WATER. 
The use of hot-water treatment for the control of cabbage black- 
leg was first suggested by Norton (8). He treated cabbage seed for 
5 minutes at 60°, 10 minutes at 56°, 15 minutes at 56°, and 20 minutes 
at 54° C. without injuring it, while spores of the fungus were killed 
at somewhat lower temperatures. The effect of these treatments upon 
the fungus within infected seeds was not determined, however. 
Table III. — Effect of hot-water treatment upon, the Mack-leg fungus within 
infected cabbage seeds and upon commercial seeds. 
Length 
of ex- 
posure 
(min- 
utes). 
Effect upon infected seeds. 
Effect upon commercial seeds. 
Seed 
lot. 
Num- 
ber of 
seeds 
used. 
Seeds 
with 
viable 
fungus 
after 
treat- 
ment 
(per 
cent). 
Seeds 
with 
viable 
fungus 
and 
ger- 
minat- 
ing 
(per 
cent). 
One-year-old seed. 
Two-year- 
old seed. 
Temperature. 
Lot 2-18.a 
Lot 4-19.& 
Lot 2-lS.o 
Ger- 
mina- 
tion 
(per 
cent). 
Seed- 
ling 
in- 
jury, c 
Ger- 
mina- 
tion 
(per 
cent). 
Seed- 
ling 
in- 
jury.c 
Ger- 
mina- 
tion 
(per 
cent). 
Seed- 
ling 
in- 
jury.c 
4-18 
1-19 
1-19 
1-19 
1-19 
1-19 
4-18 
1-19 
4-18 
1-19 
130 
24 
15 
20 
24 
35 
17 
35 
23 
24 
75.3 
66.6 


29.1 
14.2 

2.S 


22,3 









93 
O 
97 
O 
67 
o 
Do 
At 50° C 
30 
60 
5 
10 
15 
15 
20 
30 
5 
86 
85 
81 
80 
67 
67 
e 
e 
e 
e 
91 
82 
86 
86 
82 
o 
o 
o 
e 
e 
66 
46 
51 
48 
33 
e 
Do 
At 55° C 
_i. 
Do 
+ 
Do 
+ 
Do 
At 56 to 57° C . 
At 55° C 
52 
59 
+ 
39 + 
18 
+ 4 
At 60° C . 
\" 
a Wisconsin Hollander variety grown at Racine, Wis., in 1918. 
b All Seasons variety grown at La Conner, Wash., in 1919. 
c Symbols used: 0=Noinjury; ©=slight; -=-= medium; +=severe. 
The effect of hot water held at 50°, 55°, and 60° C. both upon 
commercial and infected seeds has been determined by the writer, 
and the results of the tests are given in Table III. Treatment for 30 
minutes at 55° C. completely eradicated the fungus, but considerable 
73603°— 22— Bull. 1029 2 
