STAGES OF STRUCTURAL-FUNCTIONAL REORGANIZATION DURING OVULE AND SEED DEVELOPMENT

摘要

Morphological and functional periodicity of the ontogeny is determined differently. We distinguish "stages of structural-functional reorganizations of short duration and more prolonged "periods" with a relatively constant character of developing structures in ovule and seed development Species studied differ in both the quantity and characteristics of the stages. First of all, the development is conditioned by variation in ovule and seed structure, diverse dynanu'cs of metabolite accumulation, and possibly by peculiarities of substance transport. Based on the data available, we can conclude that common stages for both the crassi-, tenui- and medionucellate ovules (archesporial cell, megaspoiocyte before meiosis, early and late globular embryos, mature embryo) explain the general direction in the formation of the reproductive structures and surrounding tissues. Specific stages may have different implications from one species to another: 1) verify that the ovule belongs to a specific type, 2) indicate their lability in different taxa with the same ovule type, 3) coincide in species with various ovule types.