Developmental Morphology of the Megasporangium and Embryogeny in Ipomoea reptans Poir. and Related Species

Abstract

In Ipomoea reptans Poir. the development of the megasporangium involves the appearance of a parietal tissue intervening between the nucellar protoderm and the primary sporogenous cell, the latter functioning directly as the megaspore mother cell. Following meiosis, the chalazal megaspore develops into a female gametophyte containing three cells in the egg apparatus, a single antipodal cell, and two polar nuclei. The development of the megasporangium is thus monosporic, its later stages being a deviation from the typical Polygonum type. The ensuing embryogeny is a variation of the Solanad type. The present paper gives a comprehensive review of literature presented by previous investigators who worked on other species in the Convolvulaceae. It is conclusively found that the development of the parietal tissue, the female gametophyte, and the embryo varies considerably among members of this family. Inconsistencies occur even among the different species of the same genus. The developmental patterns of these structures, therefore, are of little use in determining the phylogenetic relationships of plants in the Convolvulaceae.