| Abstract: | Although unchilled, intact seeds of Betula pubescens and B.verrucosa require light for germination, isolated embryos germinateequally well in both light and darkness. An aqueous extract of these seeds has germination-inhibitoryproperties correlated with the presence of a non-fluorescent,single substance. The light requirement of isolated embryosis restored by the inhibitor. When intact seeds are leachedwith water to remove some inhibitor, it is found that the lightrequirement is reduced, short days and single light periodsthen eliciting greater germination than in unleached seeds. It has been found that scratching, pricking, and cutting theseed 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 increasedin oxygen-enriched atmospheres. It has been found that although the inhibitory effect of theseed coat in intact seeds is partially due to the reductionof the oxygen supply to the embryo, a low oxygen concentrationdoes not prevent germination of isolated embryos. Experimentalresults suggest that the inhibitor in the seed coat increasesthe oxygen requirement of the embryo. |
