PISTIL STRUCTURE OF BANKSIA-MENZIESII RBR (PROTEACEAE) IN RELATION TOFERTILITY

The morphology and histochemistry of the pistil of Banksia menziesii w ere studied to determine whether the observed low fertility of the spe cies has a structural basis. The distal portion of the style, the poll en presenter, was distinct in both external and internal morphology fr om the remainder of the style. It was an elongated structure with eigh t longitudinal ridges, a swollen base, and with pollen-receptive stigm a cells enclosed within a groove located at its tip. The stigma was we t papillate, and was covered with a lipidic secretion overlying polysa ccharide-rich mucilage. Below the groove, the solid transmitting tract comprised a few thick-walled cells surrounded by numerous transfer ce lls, and vascular bundles associated with sclerenchyma. The style imme diately below the pollen presenter was constricted, and the transfer c ells ended in this region. The upper stylar cortex consisted largely o f sclerenchyma, and the transmitting tract narrowed towards the base, comprising only 10.9 +/- 0.3 cells at the junction with the ovary. The ovary contained two ovules, both of which were functional at anthesis , although the upper ovule developed more quickly than the lower. The inflorescence consisted of over 700 flowers, of which 2.5 +/- 0.2% had short styles and pollen presenters with exposed stigma papillae. Apar t from this, there was no variation in pistil structure which would ex plain the observed low fertility.