480 
Kidd and West.— The Controlling 
Table XXI. 
The Effect of High and Low Temperatures in causing Germination of 
Brassica alba Seeds showing Secondary Dormancy. 
Treatment of inhibited j 
seeds. 
Germinations after — Percentage 
3456789 10 - tim afUr 
used, day days. days. days. days. days. days. days. days. days. f a y S 
of gennina- RemarkSt 
50°C. for 3 hours, then 
returned to laboratory 
temperature. 
50°C. for | hour, then 
returned to laboratory 
temperature. 
2 5 0 C. continuously. 
Control’, inhibited seeds 
kept at laboratory tem- 
perature throughout. 
i-3°C. for 3 days, then 
returned to laboratory 
temperature. 
o° C. for 5 hours, then 
returned to laboratory 
temperature. 
~4°C. for 3 hours, then 
returned to laboratory 
temperature. 
— 7°C. for 5 hours, then 
returned to laboratory 
temperature. 
Control : inhibited seeds 
removed to fresh sand at 
laboratory temperature. 
20 
20 
12 
13 
15 
17 
18 
20 
0 
2 
2 
4 
5 
20 
0 
3 
4 
5 
5 
5 
20 
0 
0 
0 
0 
0 
0 
0 
50 
0 
0 
0 
0 
0 
0 
0 
50 
16 
17 
25 
10 
10 
10 
5° 
0 
0 
0 
0 
0 
0 
0 
10 
0% 
90 % 
25% 
25% 
0% 
0% 
34% 
40 % 
0% 
All dead. 
All healthy seed- 
lings. 
All healthy seed- 
lings. 
The ungerminated 
seeds were killed. 
Mean temperature of laboratory, i6°C. 
The above results indicate that germination can be induced by short 
exposure to the extremes of high or low temperature which just fall short 
of injury ; exposure to intermediate temperatures, either for a short period 
or continuously, has no effect. Thus, exposure to 50° C. for half an hour was 
followed by 90 per cent, germinations, but exposure for three hours to the 
same temperature was fatal, while continuous exposure to 25 0 C. had no 
effect. In a similar way, exposure to — 7°C. for five hours resulted in 
40 per cent, healthy germinations, but the remaining 60 per cent, were 
killed. 1 Exposure to o° C. for three days, on the other hand, had no effect 
in causing germination of inhibited seeds. 
1 In this connexion it is interesting to note that fully swollen normal seeds of Brassica alba 
submitted to the same temperature (i. e. — 7 0 C.) in parallel with the above experiment showed 
marked injury without exception. The sharp contrast in this case between the 10 seeds which 
germinated in the normal manner and the 15 which did not germinate, and which when tested 
by removal of the testa proved to be killed, is probably to be accounted for by the fact that the 
injurious effect of low temperatures is due to the formation of ice-crystals which would occur at 
a critical point depending upon the concentration of the cell-sap. 
