AN EMBRYOLOGICAL STUDY OF PLATANTHERA-BIFOLIA (ORCHIDACEAE)

Flowers of Plantanthera bifolia were hand-pollinated and fixed in FPA50 after 2, 5, 7, 14, and 21 days. Ovules, made transparent in Herr's clearing fluid, were investigated using confocal scanning laser microcopy. Pollination initiates the megasporogenesis. Two days after pollination dyads are frequent. Three days later most embryo sacs contain two nuclei. Seven days after pollination the embryo sacs are 4 - 8-nucleate and some are organized, and a week later all embryo sacs are organized and fertilization takes place. The embryo sac development follows the Polygonum type. Twenty-one days after pollination the egg nuclei have been fertilized and the embryo sacs contain 2- to many-celled embryos. A suspensor is formed during early stages of embryo development but degenerates later. Fertilization of the central nucleus does not lead to endosperm development.