479 
Influence of Carbon Dioxide . 1 V ’. 
fully swollen seeds at a later stage of development after the process of 
cell division has advanced results in injury; (iii) that both injury and 
acceleration of germination are due to changes of the same nature re- 
sulting from redrying ; and (iv) that in the case of secondarily dormant 
seeds the effect of redrying, while not causing injury owing to the absence 
of cell-division, is not only sufficient to break up the dormant condition 
of the embryo, but also to cause acceleration of germination. 
A series of experiments was conducted to test the reaction of redried 
inhibited seeds to carbon dioxide with regard to inhibition. It was found 
that a smaller concentration of carbon dioxide was required to initiate 
inhibition than that required in the case of normal seeds. The following 
table gives the results of one set of experiments in which the control 
non-inhibited seeds soaked and redried are compared with inhibited seeds 
which have been previously inhibited and redried during secondary 
dormancy : 
Table XX. 
The Increased Sensitiveness of Redried Inhibited White Mustard Seeds 
to the retarding and inhibiting Action of Carbon Dioxide. 
Number of seeds still 
Percentage o/C 0 2 Number of germinations after — ungermmated after a 
(20% oxygen in each case). 46 hours. 97 hours. 120 hours. jurther 13 ays m 
0°/ ! 
1 A 
20 
20 
j 
(B 
20 
20 
20 
5 %j 
, A 
*9 
20 
20 
B 
16 
17 
19 
i°% j 
A 
B 
18 
5 
J 9 
12 
*9 
12 
•6% j 
, A 
' B 
17 
0 
18 
3 
18 
3 
<L) <u tj o 
4 
9 
20 seeds used in each experiment. 
Temperature I7-I9°C. 
In light. 
In each case seeds A and B were set side by side in the same flask. 
A ~ control non-in- 
hibited seeds soaked 
and redried. 
B = inhibited seeds 
showing secondary 
dormancy redried. 
Similar results were obtained when fresh control seed was used. The 
increased sensitiveness to the influence of carbon dioxide is clearly due to 
the fact of previous inhibition and not to the fact that the seeds have been 
soaked and redried. As will be seen also from the above table, secondary 
dormancy is again produced when redried inhibited seeds are submitted to 
the influence of carbon dioxide under germinating conditions a second time. 
Temperature. The following table gives the results of experiments 
in which the endeavour was made to bring about germination of seeds 
showing secondary dormancy by exposure to high or low temperatures : 
