This thesis consists of three main parts, viz., of an exhaustive historical survey of the study of the structure and development of ovules and seeds (p.l2-p.50) and some other introductory chapters (p.51-p.75), of digests (with some additions), of papers previously published by the author on integument initiation in representatives of the Juglandaceae, Liliaceae, Lactoridaceae, Magnoliaceae, and Winteraceae (p.76-p,118), and of original reports on integument and seed coat ontogeny in members of the Cruciferae, Euphorbiaceae, and Oxalidaceae (p. 119-p.l60). Some new data are reported: a subdermal initiation of the inner integument in Euphorbiaceae, the incidence of various types of initiation and histogenesis of integuments among the Cruciferae, the singular development of the vascular strands in the outer integument of Lunaria, and the unusual structure of the testa in seeds of species of Oxalis and Biophytum with a ballistic ejection mechanism of the seed accomplished by means of a preformed separation zone in, and the sudden rupture of the outer testa layers.