Dormancy in Seeds of Hibbertia hypericoides (Dilleniaceae)

Seeds of Hibbertia hypericoides (DC.) Benth. (Dilleniaceae), a shrub native to the south-west of Western Australia, exhibit both seed coat dormancy and embryo dormancy. Water uptake was passive and germination poor after an experimental time period of 3 months in mature, potentially viable seeds. After removal of the seed coat, imbibition occurred in three phases and resulted from passive hydration and active metabolic processes. In mature, potentially viable seeds low water uptake is due to the heavily cutinised cells of the endotesta, since immature, potentially 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 potentially viable seeds. However, the low proportion of vigorous seedlings after seed coat removal suggests that the minute, underdeveloped embryo itself is dormant. Seed coat removal therefore appears to lead to the precocious germination of immature, presumably still partly dormant embryos. Gibberellic acid (GA3) did not affect the germination of seeds. Preliminary experiments do not suggest that the seed coat contains chemical inhibitors.