The life cycle of plants alternates between a haploid gametophyte and a diploid sporophyte. In higher plants the gametophyte is reduced to a small number of cells surrounded by sporophytic tissue. The female gametophyte is contained within the ovule and consists of an embryo sac which harbors the egg cell and other associated haploid cells required for fertilization and development of the embry...

The plant life cycle is characterized by the alternation of generations between a diploid sporophyte and a haploid gametophyte. The sporophyte functions to produce spores, which then develop into gametophytes. The differentiated gametophytes in turn produce either the male gametes (sperm) or female gametes (egg cells). In contrast to lower plant species, in which the gametophyte is the dominant...

Rhoades (1941) found recombination in the proximal regions of chromosome 5 to be higher in male than in female flowers. Two explanations were proposed to account for the lower female values, namely: (1) there is a basic difference in rates of crossing over in mega- and microsporocytes, or (2) selective orientation of the chromosome 5 bivalent on the meiotic spindle leads to the preferential seg...

INTRODUCTION In sexually reproducing organisms, gametes are generated by a specific lineage derived from somatic cells that undergo a somaticto-reproductive cell fate transition (SRT). In mammals, the primordial germ cells (PGCs) differentiate in the embryo at gastrulation stage (Bendel-Stenzel et al., 1998). By contrast, the spore mother cells (SMCs) of flowering plants are formed in the adult...

The calcareous concretions studied formed in different depositional environments associated with the Pcnnsylvanian eyclothems of cast central Ohio. The late syngenetic to early diagenetie coal balls from Lower Frecport Coal in Jefferson County were formed by cellular permineralization of decaying terrestrial plants in a peat swamp. These coal balls, composed of N9.N% calcite, 7.0% pyrite, and 2...

Thirty-one specimens of a small megasporangiate lycopsid cone referable to the genus Porostrobus Nathorst and abundant associated dispersed megaspores have been collected from Early Pennsylvanian strata in the Allied Stone Company quarry, Milan, Illinois. Based on other elements in the flora, the deposit is considered to be part of the Morrowan Caseyville Formation and probably of Namurian age....

introduction maceral is a term to introduce organic components visible under a microscope (stopes, 1935). the physical and chemical characteristics of macerals such as elemental composition, moisture content, hardness, density and petrographic characteristics differ. the differences in the physical and chemical characteristics of macerals are reflected in their industrial behavior.(parkash, 198...