Embryological studies in the compositae. II. Sporogenesis, Gametogenesis, and Embryogeny in Ammobium alatum R. Br.

Abstract

Ammobium alatum is a perennial herb whose discoid-homogarnous capitula are surrounded by several rows of involucral bracts with white radiating laminae.

Four microsporangia are present in each anther and their development and dehiscence are described.

The ovule is anatropous, unitegmic, and tenuinucellate. The archesporial cell is hypodermal in origin and, following considerable increase in size, it functions directly as the megaspore mother cell. Cytokinesis and wall formation are postponed until after Meiosis 11 and a dyad is formed in which each cell is binucleate. The embryo sac is bisporic and its development is a variation of the Allium type. After fertilization, the surviving synergid may increase greatly in size but it does not extend into the micropyle and it collapses when the embryo reaches the seventh cell generation.

Embryogeny is of the Asterad type and the sequence of events leading up to maturation of the embryo and of the fruit is described.