A Nomarski Interference Study of Megasporogenesis and Megagametogenesis in Smelowskia Calycina (Cruciferae)

Abstract

Ovule development, megasporogenesis and megagametogenesis in an aneuploid population of the arctic‐alpine crucifer, Smelowskia calycina, were examined to test for the possibility of apomictic seed production. Whole mounts of ovules cleared in Herr's “4½” clearing fluid were examined using Nomarski differential interference microscopy. The campylotropous ovule was bitegmic, with a micropyle formed by both integuments. The single archesporial cell of a crassinucellar nucellus functioned directly as a megasporocyte, dividing to form a linear tetrad of megaspores. The chalazal megaspore divided to form an 8‐nucleate, 7‐celled gametophyte of the Polygonum type, having hooked synergids with a well‐developed filiform apparatus and polar nuclei that fused prior to fertilization. In the absence of any anomalous development indicative of agamospermy, seed production was assumed to be sexual.