Megasporogenesis and Development of Embryo Sac in Crocus Sativus

SUMMARYCytological observations during megasporogenesis and embryo sac development of Crocus sativus L. are reported. During meiotic divisions irregular assortment of chromosomes was observed; consequently, megaspores resulted numerically variable (4–6) and they were genetically unbalanced. The megaspore tetrads-hexads showed chalazal heteropolarity, however, the microphylar pole resulted more active than the chalazal one in promoting megaspore development. This was attributed to the nutritional factors liberated from degenerated micropylar spores. Independently on the number of produced megaspores the micropylar ones (M1, M2, M3), generally, degenerated, the chalazal spores (M4–M6) persisting; therefore, besides single embryo sacs, megaspores close to embryo sac or development of two embryo sacs could be observed. Frequently, the megasporogenesis or development of the persistent megaspore were not completed; consequently, ovules lacking embryo sac or showing immature embryo sac occurred. The mature embry..