Influence of Carbon Dioxide. IV. 459 
to carbon dioxide and oxygen for the production of secondary dormancy 
as^an ‘ after ’-effect. 
In these experiments an arbitrary period of ten days was allowed 
before determining the number of seeds showing secondary dormancy. 
This period was chosen as a result both of our general experience and of 
specific experiments, to one of which we have already referred. In result 
it was found that a high percentage of seeds showing prolonged secondary 
dormancy could only be obtained under quite limited conditions. 
Oxygen. 
The following experiments deal with the question as to how far the 
degree of secondary dormancy is influenced by the concentration of oxygen 
used during the primary period of inhibition. Two series were conducted : 
Table II. 
Effect of various Partial Pressures of Oxygen (25 per cent. Carbon Dioxide 
present ) on the Production of Secondary Dormancy in Seeds of Brassica 
alba. 
io 
■SO 
8 e 
1“ 
Days. 
->8 K 
-.8 a 
v! 
8 § 
; St §> 
! £ 
. -^,.8 
k 8 <0 
*1 
Germinations after removal 
of the seeds to air. 
Number of days — 
345 6 7 8 9 10 
1 b 
. 
1 
1 h 
1 1-3 
S *-» 
O % ^ « 
4* 8 /-v ^ 
. o *8 
■*» « 
8 ^ ' 
^ | § 
30 
0% 
21 
0 
30 
3 
8 
13 
16 
16 
16 
18 
22* 
0% 
80% (approx.) 
30 
0% 
15 
0 
30 
0 
5 
13 
19 
21 
24 
24 
24* 
0% 
60% 
30 
5 % 
21 
0 
3 ° 
8 
9 
12 
12 
12 
12 
13 
14 
53 % 
23% 
50 
20 % 
17 
7 + 
43 
0 
1 
1 
1 
2 
2 
2 
2 
96 % 
5 % 
30 
3 °% 
21 
15+ 
i 5 
0 
0 
0 
0 
O 
0 
I 
1 
93 % 
0% 
30 
75 % 
21 
14+ 
16 
0 
1 
1 
2 
2 
2 
3 
3 
81 % 
6 % 
Mean temperature of laboratory during inhibition period, if 0 . 
* Remainder dead. 
+ All showing injury to radicle. 
with 25 per cent, carbon dioxide present (Table II) ; and with 35 per cent, 
carbon dioxide present (Table III). The amount of oxygen present was 
found to influence the degree of secondary dormancy. Thus in Table II 
it is seen that with concentrations of oxygen below 20 per cent., the 
percentage of seeds showing secondary dormancy decreases with the fall 
of oxygen. With 20 per cent, oxygen present 96 per cent, of the 
seeds show secondary dormancy, and higher concentrations of oxygen 
have little effect, the percentage of seeds showing secondary dormancy 
remaining high. 
I i 
