Polygonum Type Of Development Research Articles

Gametogenesis in Galbulimima belgraveana (Himantandraceae)

The flowers of Galbulimima belgraveana (F. Muell.) Sprague are bisexual, calyptrate and protogynous. The numerous free stamens are laminar and arranged spirally on an elongated receptacle; only the middle stamens are fertile. There are four microsporangia embedded on the abaxial side of the microsporophyll. The tapetum is secretory and often double. A variety of spore tetrad types is produced. The mature pollen grains are single, monosulcate, scabrate, atectate, spheroidal and 2-celled. The carpels of a flower are initially free but later become concrescent so that a single fruit is formed. The ovules are anatropous, crassinucellar and bitegminal, and show an elongated embryo sac that conforms to the polygonum type of development. There is a massive parietal tissue in early stages of ovule development. In its embryological features, the species shows close relationships to the families Annonaceae and Degeneriaceae and, to a slightly lesser extent, the Magnoliaceae and Eupomatiaceae.

EFFECTS OF SPACE FLIGHT (BIOSATELLITE II) AND RADIATION ON FEMALE GAMETOPHYTE DEVELOPMENT IN TRADESCANTIA

The mode of female gametophyte development and the cytological effects of orbital flight factors, with and without radiation, on embryo sac development were studied in Tradescantia clone 02 flown in Biosatellite II. One package of 32 rooted inflorescences was exposed during the free‐flight phase of the two‐day orbital flight to about 220 R gamma radiation from an 85Sr source, and a nonirradiated package was flown as a flight control. Two similar packages, one irradiated and one unirradiated, were maintained in a ground‐based vehicle as concurrent nonflight controls. Various postflight ground experiments were conducted in an attempt to associate with specific flight factors the effects observed in the orbited plants. Mature ovaries were fixed daily as the flowers opened for at least 20 days after the treatment, sectioned, stained, and analyzed for the rate of embryo sac abortion and other developmental abnormalities. The embryo sac in Tradescantia clone 02 is eight‐nucleate with a Polygonum type of development. Irradiation during megasporogenesis produced an increased rate of embryo sac abortion and this radiation effect was greater in the environment of the flight vehicle than in the nonflight vehicle. This effect may be due to an increase in concentration of ethylene in the flight vehicle. A synergism between some undetermined flight factor and radiation was found to produce underdeveloped embryo sacs. Malfunctioning of the spindle, most probably due to free flight, was evidenced by the increased number of embryo sacs with misoriented nuclei.

Some aspects of the life history of Callistemon citrinus (Curt.) Skeels

Pollen development is irregular in native populations but regular in the cultivated plants investigated. Development of the anther wall is of the Basic type and the tetrasporangiate anthers shed their pollen at the two-celled stage through longitudinal slits. The single vascular bundle of each stamen gives off two traces in the connective. The ovules are anatropous, crassinucellar, and bitegmic. The swollen distal ends of both integuments form the micropyle. The single archesporial cell cuts off a parietal cell, and during megasporogenesis a one- to three-layered parietal tissue is formed which collapses during the development of the embryo sac. Occasionally the megaspore mother cell degenerates but in these instances the growth of the ovule is unimpaired. The female gametophyte follows the Polygonum type of development, and when mature is eight-nucleate and includes three ephemeral antipodal cells. Some abnormalities pertaining to the number and arrangement of nuclei in the embryo sac have been observed and hardly 4% of the ovules form fertile seeds. The seed coat is formed from both the integuments. A hypostase is differentiated in the seed.

A contribution to the life history of Angophora floribunda (Sm.) Sweet (Myrtaceae)

The flower buds of Angophora floribunda appear in the last week of November and anthesis occurs in the middle of January the following year. There is no prolonged resting phase at any stage during embryology and the seeds are shed during late February to early March. In floral development, the petals are the last structures to be formed. Early anther development precedes corresponding stages in the ovules of the same flower, but events in the ovules proceed more rapidly and meiosis occurs simultaneously in the spore mother cells of both organs. The mature two-celled pollen grains are shed when the ovules contain four-or eight-nucleate embryo sacs. Many flowers bear anthers containing only sterile pollen grains, which occur either singly or as tetrads. Various abnormalities in the development of the pollen are reported, and the anthers containing sterile pollen neither develop fibrous bands in the endothecium nor do they dehisce. The ovules are bitegminal, crassinucellar, and hemianatropous. Occasional bifurcation of the inner integument was observed and a hypostase differentiates at the four-nucleate stage of the embryo sac. The embryo sac follows the Polygonum type of development and is five-nucleate and four-celled when mature. The endosperm is Nuclear in origin, and in about half the seeds examined a granular unidentified substance accumulates in the embryo sac. The development of the embryo is irregular and the seedlings bear a collar-like structure at the junction of the hypocotyl and the radicle. The mature embryos are usually dicotyledonous but rarely tricotyledonous. The seed coat is formed exclusively by the outer integument; in the ripe seed it consists of an outer epidermis of large, palisade-like, thin-walled, tanniniferous cells and an inner crystalliferous layer.