The Role of Germination Inhibitors and Oxygen in the Dormancy of the Light-densitive Seed ofBetulaspp.

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Abstract
Although unchilled, intact seeds of Betula pubescens and B. verrucosa require light for germination, isolated embryos germinate equally well in both light and darkness. An aqueous extract of these seeds has germination-inhibitory properties correlated with the presence of a non-fluorescent, single substance. The light requirement of isolated embryos is restored by the inhibitor. When intact seeds are leached with water to remove some inhibitor, it is found that the light requirement is reduced, short days and single light periods then eliciting greater germination than in unleached seeds. It has been found that scratching, pricking, and cutting the seed coat increases the germination of intact seeds in darkness, and that this is probably due to enhanced oxygen entry. Further, it has been found that germination in short days is increased in oxygen-enriched atmospheres. It has been found that although the inhibitory effect of the seed coat in intact seeds is partially due to the reduction of the oxygen supply to the embryo, a low oxygen concentration does not prevent germination of isolated embryos. Experimental results suggest that the inhibitor in the seed coat increases the oxygen requirement of the embryo.