DORMANCY IN SEEDS OF HIBBERTIA HYPERICOIDES (DILLENIACEAE)

Seeds of Hibbertia hypericoides (DC.) Benth. (Dilleniaceae), a shrub n ative to the south-west of Western Australia, exhibit both seed coat d ormancy and embryo dormancy. Water uptake was passive and germination poor after an experimental time period of 3 months in mature, potentia lly viable seeds. After removal of the seed coat, imbibition occurred in three phases and resulted from passive hydration and active metabol ic processes. In mature, potentially viable seeds low water uptake is due to the heavily cutinised cells of the endotesta, since immature, p otentially viable seeds and non-viable seeds, which both have a weakly cutinised endotesta, imbibed water readily. Removal of the seed coat significantly increased the final germination percentage in potentiall y viable seeds. However, the low proportion of vigorous seedlings afte r seed coat removal suggests that the minute, underdeveloped embryo it self is dormant. Seed coat removal therefore appears to lead to the pr ecocious germination of immature, presumably still partly dormant embr yos. Gibberellic acid (GA(3)) did not affect the germination of seeds. Preliminary experiments do not suggest that the seed coat contains ch emical inhibitors.