Embryology of the dioecious Australian endemic Lomandra longifolia (Lomandraceae)

Microsporogenesis, embryogeny and endosperm development of Lomandra longifolia Labill. are described in detail. The formation of the anther wall is the basic type composed of four cell layers, namely an epidermis, an endothecium, one middle layer and a tapetum. The tapetum layer has glandular, uninucleate cells. Successive cytokinesis follows meiosis, subsequently forming a tetrahedral tetrad of microspores. The ovule in each carpel is hemitropous, crassinucellate and bitegmic, with the micropyle formed by the inner integument. The archesporial cell divides periclinally to form the primary parietal and primary sporogenous cells. The sporogenous cell functions as the megaspore mother cell, whereas the parietal cell divides to give rise to two parietal layers. The mature megagametophyte, which has enlarged synergids and antipodals, is of the Polygonum type, with the normal complement of seven cells and eight nuclei. Nucellar tissue in the mature ovule consists of enlarged dermal cells and irregular subdermal cells surrounding a central strand of markedly smaller cells. Endosperm development is of the nuclear type. Embryo development is of the Graminad type, characterised by oblique zygotic and early pro-embryonic divisions.

Embryology and Reproductive Ecology of the Darling Lily, Crinum flaccidum Herbert

In Crinum flaccidum the anthers are versatile and tetrasporangiate with a secretory tapetum of binucleate cells. Successive cytokinesis in microspore mother cell results in isobilateral and decussate microspore tetrads. The mature pollen grains are single, spheroidal, disulculate, echinate and 2-celled. In the mature anthers, fibrous thickenings develop not only in the endothecium but also in two or three middle cell layers and the connective tissue before latrorse dehiscence. A lobed tissue in each of the three locules of the ovary serves ovular and placental functions. Each extension of the 5-7 paired lobes represents an ategmic ovule. The development of the female gametophyte conforms to the Polygonum type. Usually only one gametophyte is present in each lobe but occasionally several may occur. Bulb growth is monopodial with normally three umbels produced per plant, each carrying an average of 10 flowers, only two or three of which are open at any one time. Nectar sugar concentration was measured at 14.2% (w/w), of which 44.8% of solids was sucrose and 3.9% either glucose or fructose. The protandrous flowers are phalenophilous, pollinated by sphingid moths. The endosperm formation is of the nuclear type. In the absence of seed coats and the nucellus at maturity, the outer layers of the endosperm become corky following the activity of a phellogen. Embryogeny appears to be of the Asterad type. The mature embryo is straight and chlorophyllous. The large (5.3 g) seeds are 89% water and show no dormancy, germinating without an external supply of water, sometimes while still on the parent plant.

The floral morphology and embryology of Themeda australis (R. Br.) Stapf

A comparative study was carried out between diploid and tetraploid races of Themeda australis from Armidale and Cobar, respectively. Some morphological variations occur in both populations, but sporogenesis and gametogenesis are identical. The anther is tetrasporangiate and the development of its four-layered wall is described. The tapetum is of the secretory type and its cells become binucleate at the initiation of meiosis in the adjacent microspore mother cells which undergo successive cytokinesis. Microspore tetrads are usually isobilateral and the pollen grains are three-celled at dehiscence, which takes place by lateral longitudinal slits. The ovule is of a modified anatropous form and bitegmic, the broad micropyle being formed of both integuments. The single hypodermal archesporial cell develops directly into the megaspore mother cell and the nucellar epidermis undergoes periclinal and anticlinal divisions to form a conspicuous epistase. The chalaza1 megaspore of the linear tetrad gives rise to a Polygonum-type embryo sac. Material from the Armidale population showed one embryo sac per ovule, but two to five embryo sacs were present in that from Cobar. Embryogeny is typically graminaceous and endosperm formation is at first free-nuclear, later becoming cellular. Polyembryony follows fertilization of several embryo sacs within the same ovule. The reasons for low fertility of T. australis and poor germination of seeds are discussed.