Botanical Gazette, 67(3): 269-270 (Mar 1919)
Secondary dormancy in seeds.
William Crocker

KIDD and WEST.3 have continued the study of the controlling action of carbon dioxide on the germination of seeds of Brassica alba. In two previous papers by the senior author it has been shown that low concentrations of carbon dioxide inhibit the germination of seeds, and that temperature and oxygen pressure determine the concentration necessary to inhibit germination. In normal oxygen pressure 2-4 per cent carbon dioxide will inhibit germination at 3° C., while at 20° C. it requires 20-25 per cent. At 17° C. it requires 9-22 per cent carbon dioxide to inhibit with 5 per cent oxygen pressure and 20-25 per cent carbon dioxide with 20 per cent oxygen pressure. All seeds studied, except Brassica alba, germinate normally as soon as the carbon dioxide is removed, while B. alba remains dormant after the carbon dioxide is removed. The authors term this "secondary dormancy," in agreement with the usage of this term by CROCKER.

In the production of secondary dormancy the authors note the following general facts: (1) secondary dormancy is not produced if oxygen is absent during the primary period of inhibition or if carbon dioxide has been used in too high concentration; (2) conditions during the primary period of inhibition which prevent subsequent occurrence of dormancy are the ones that exercise injury on the radicle; (3) 100 per cent dormancy is obtained only within narrow limits of carbon dioxide and oxygen pressure. Secondary dormancy is not produced by a change in the permeability of the coats to gases or water, or to an increase in their breaking strength, but by a change in the embryo by which it becomes less responsive to germinative conditions. The following conditions caused the secondarily dormant seeds to germinate: removal or partial removal of the testa; redrying of the soaked seeds; short exposures to high or low temperatures; treatment with acids (especially n 0.01 HCl and propionic); treatment with high concentrations of carbon dioxide followed by germination in air. High partial pressures of oxygen had no effect on the germination of secondarily dormant seeds.

The authors give the following interpretation of this work: "It will be seen that the main interest of this communication centers around the causes underlying the initiation of growth rather than in the conditions of dormancy. In considering this question of growth in the case of seeds of B. alba, our experiments show clearly that there is no question of limiting factors. We have been able to trace no limiting factor responsible for the non-germination of white mustard seeds showing secondary dormancy. We find ourselves rather in the presence of facts which emphasize a conception of stimulus. It has been seen that widely different treatments, quite unclassifiable in any feature other than that they all result in injury and death, if carried too far, excite germination and growth of white mustard seed. It appears to us probable that some return will have to be made to this conception of stimulus in plant physiology generally, and that in any experimental analysis of the living plant, as a unit and in relation to its life-cycle, the idea of limiting factors, which has so long dominated the minds of plant physiologists, will have to be modified."

  1. KIDD, F., and WEST, C., The controlling influence of carbon dioxide. 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 phenomena. Ann. Botany 31:457-487. 1917.

Crocker Bibliography