460 
Kidd and West. — The Controlling 
In Table III the results are of a similar nature. In the absence of 
oxygen no secondary dormancy is obtained, whereas with 1 5 per cent, or 
30 per cent, oxygen present approximately half the seeds exhibit secondary 
dormancy. The fact that the amount of secondary dormancy obtained 
Table III. 
Effect of various Partial Pressures of Oxygen (35 per cent. Carbon Dioxide 
present) on the Production of Secondary Dormancy in Seeds of Brassica 
alba. 
1? 
§ 
50 
50 
50 
.1 •• I ' 
* o w 
$ 
0% 
15% 
30% 
Days. 
•s ^ s 
"Ka ^ 
X 52 
X § °-0 
ss 
c £ 
o 
5 
3 
^ £ 
Germinations after removal 
•X . 
Wt-i 
kl 
of seeds to air. 
Days. 
4 
5 
6 
7 
8 
10 
50 
1 7 
2 3 
2 7 
3<3 
3 2 
35* 
45 
4 
13 
15 
17 
22 
H 
47 
4 
12 
13 
13 
17 
22 
Mean temperature of laboratory during inhibition period, 
* The 1 5 ungerminated seeds were dead. 
8*1 • 
1 
f.&Si 
I 
$*3 
0% 
47% 
53 % 
C. 
13 
^ fl ^ 
^4 <2> .Sf 
"X « 
X -5i 
*3 
: k x 
78 % 
10% 
4 % 
with 35 per cent. C 0 2 does not rise much above 50 per cent, in comparison 
with the 96 per cent, of secondary dormancy obtained with 25 per cent. 
C 0 2 finds an explanation in the following section dealing specifically with 
the effect of various concentrations of carbon dioxide on the production of 
secondary dormancy. 
It thus appears that for the production of secondary dormancy the 
seeds must be supplied with oxygen during the primary period of direct 
inhibition by carbon dioxide. 
In the last column of the above tables the percentage of seeds (other 
than those germinating in the presence of the inhibiting gas=-mixtures) 
which showed injury to the radicle is given. A marked correlation appears 
between the injury to the radicle and percentage of seeds showing secondary 
dormancy : the greater the injury the less the amount of secondary dormancy 
produced. 
Where secondary dormancy is almost complete , the percentage of seeds 
showing injury is practically nil. In fact it may be said that any seed 
which after ten days in air shows typical secondary dormancy (in other 
words, is practically indistinguishable from a newly swollen normal seed) 
is certainly uninjured with regard to the radicle. The condition with 
regard to injury or non-injury of the seeds showing secondary dormancy 
was examined by the removal of the seed-coats, a treatment which, as 
pointed out in a previous paper (Kidd, 1 , p. 416), will cause germination 
at any time during the period of secondary dormancy. 
