Investigations on gametogenesis and developmental anatomy of achene in Crepis japonica benth (Inuloideae, Asteraceae)

摘要

The investigation deals with gametogenesis and developmental anatomy of achene in Crepis japonica Benth. (Inuloideae, Asteraceae). Anthers are bisporangiate and the development of the sporangial wall corresponds to the Dicotyledonous type. Tapetum is of the periplasmodial type. At anthesis, pollen grains are 3- celled. Ovule is anatropous, unitegmic and tenuinucellate. The single, massive integument is collectively organized from the derivatives of the dermatogen, subdermatogen and inner core. Cells of the endothelium remain uniseriate and uninucleate throughout and is completely absorbed in the mature seed. Usually the chalazal megaspore develops into a Polygonum type of embryo sac. Very rarely, the subchalazal megaspore is functional. The funicular obturator helps in directing the growth of pollen tube towards the micropyle. Fertilization is porogamous. The endosperm is ab initio cellular. At the late globular embryo stage, 1 or 2 haustorial projections arise from the chalazal end of the endospermous tissue which embed into the surrounding ovular tissue. Embryo development corresponds to the Asterad type. In the mature seed, the testa is reduced to 4 layers of which the outer layer becomes strongly thickened. The pericarp lacks anatomical differentiation. Numerous, 1-celled trichomes develop from the epidermal layer and these persist in the mature achene.