Structure and Development of the Caryopsis in Some Indian Millets. VI. Setaria italica

Abstract

1. Each spikelet in Setaria italica Beauv. is borne lateral to a bristle axis as are also the smaller bristles of a bristle shoot to a principal bristle axis. Therefore, the bristle shoot as a whole, and not the individual bristle, must be regarded as the morphological and homologous equivalent of a spikelet. 2. Microsporogenesis in this species is normal, and the divisions are of the successive type. The pollen grains are three-celled at shedding. 3. The ovule is anatropous, bitegmic, and crassinucellate. A narrow endostome, formed by the excessive growth of the inner integument, is hooded by part of the outer integument. A pair of nucellar cells abutting the micropyle becomes hypertrophied and richly protoplasmic. 4. A linear tetrad of megaspores is formed, and the innermost is functional. The embryo sac is organized in the usual fashion. Rarely the egg shows conspicuous lateral hooks otherwise found only in synergids. The synergids and the several, multinucleate antipodal cells commence to degenerate b...