464 
Kidd and West . — The Controlling 
alba seeds, it appears (i) that the phenomenon does not occur if oxygen 
has not been present during the primary period of inhibition or if carbon 
dioxide has been used in too high a concentration ; (ii) that those conditions 
during the primary period of inhibition which prevent the subsequent 
occurrence of secondary dormancy, are found at the same time to exercise 
an injurious effect upon the radicle which is visible when the seeds subse- 
quently germinate, and that a correlation exists therefore between internal 
changes in the radicle resulting in injury and occurrence of germination. 
The relation of secondary dormancy to the conditions of oxygen and 
carbon dioxide concentration used during the primary inhibition period 
can be clearly seen from the accompanying diagram (Text-fig. 1). An 
‘ after ’-effect amounting to ico per cent, secondary dormancy is only 
obtained within quite narrow limits of possible inhibiting mixtures of 
carbon dioxide and oxygen. It is only in the region of carbon dioxide 
concentration immediately above the critical concentration needed to 
produce inhibition, that the maximum degree of secondary dormancy is 
obtained. 
Relation between the Percentage of Secondary Dormancy produced and the 
Duration of the Primary Period of Inhibition in the Presence of Carbon 
Dioxide. 
In addition to the facts described above with regard to the influence 
of excess of carbon dioxide or lack of oxygen during the primary period 
of inhibition upon the degree of secondary dormancy, it has been found 
further that the percentage of secondary dormancy is dependent upon the 
length of the primary period of inhibition in the presence of carbon dioxide. 
Tables VII and VIII give the results obtained in two experiments. It is 
clear that the full effect of secondary dormancy is not produced at all 
quickly, but that at ordinary temperatures a period of two to three weeks 
in the presence of carbon dioxide is required. The significance of this fact 
will be discussed later. 
Table VII. 
Time Factor in the Production of Secondary Dormancy . 
Number of days in the gas* 
mixture (20 % C0 2 = 
16 % o 2 ). 
3 
IO 
17 
Germinations 
10 days after removal 
from the inhibiting 
gas-mixture. 
100 % 
66 % 
57% 
17% 
Approximate percentage of 
secondary dormancy, 
0 % 
34% 
43% 
83% 
30 seeds in each experiment. Mean temperature of laboratory, I 2 » 5 °C. (in the dark) 
