The Controlling Influence of Carbon Dioxide. 
IV. On the Production of Secondary Dormancy in Seeds 
of Brassica alba following Treatment with Carbon Dioxide, 
and the Relation of this Phenomenon to the Question of 
Stimuli in Growth Processes. 
BY 
FRANKLIN KIDD, M.A., D.Sc., 
Fellow of St. John's College , Cambridge , 
AND 
CYRIL WEST, A.R.C.Sc., B.Sc. 
With Plate XXIII and five Figures in the Text. 
Contents. 
PACE 
§ i. Introduction 457 
2. The Production of Secondary Dormancy in Seeds of Brassica alba . . 458 
3. Changes in the Seed-coat or Embryo of Brassica alba accompanying the 
Production of Secondary Dormancy 465 
4. Methods of forcing Germination of Brassica alba Seeds showing Secondary 
Dormancy 476 
5. Summary 483 
6. Conclusions 485 
Appendix 485 
§ 1. Introduction. 
I N previous papers (Kidd, 1 and 2) it has been shown that carbon dioxide 
in relatively small quantities in the atmosphere inhibits the germination 
of seeds. The actual percentage of carbon dioxide required to produce 
inhibition was found to vary with temperature and with oxygen supply. 
At 3 0 centigrade 2 per cent, to 4 per cent, carbon dioxide produced in- 
hibition, whilst at 20° centigrade 25 per cent, to 30 per cent, carbon dioxide 
was required. With 5 per cent, oxygen, 9 per cent, to 12 per cent, carbon 
dioxide produced inhibition, but with 20 per cent, oxygen 20 to 25 per cent, 
carbon dioxide was required (temperature 17 0 C). 
In all seeds tested, except those of Brassica alba , germination in the 
normal way was found to follow the removal of the inhibiting carbon 
dioxide. In the case of Brassica alba seeds, the dormancy induced by 
carbon dioxide continued, however, after the removal of the inhibiting 
[Annals of Botany, Vol. XXXI. Nos. CXXIII and CXXIV. July and October, 1917.] 
