Plant Ephedra is sporophyte in nature and its life cycle shows alternation of generation.
Sporophytic phase:
Ephedra plant is small woody much branched shrub. Plant body has branched stem and bear minute scale like leaves in pairs at each joint. Plant Ephedra is mostly dioecious although there is tendency to produce microsporangia and megasporangia together.
Both the male and female reproductive organs are brone on small strobil, the scales of which are arranged in pairs. Strobili are borne as small spikes at the nodes.
Mule strobili:
They develop in the axils of leaves. They arise in whorls of 2, 3, or 4 from nodes of branches. Each stenobilus possesses a canal axis on when are borne 2 to 8 pairs of bracts. Lower one or two bracts may be sterile, rest fertile. In this axils of fertile bract arise male flowers. One male flower arises in the axil of a bract.
Each male flower is annually and has an axis and a pair of thin opposite scales for branches. Axis at apex bears 1 to 8 anthers (microsporangia). These microsporangia possess 2 or 3 locuh. Each loculuc opens by terminal slit to release microspore, or pollen grains.
Microsporangensis:
In the development of microspores the archegonial cells are hypodermal in origin. The archegonial cells are divided by periclimical division and form primary parietal cells and central primary sporangenous cells. Primary parital cells also cut off to form a layer of lapetum. Primary sporogenous cells form microspore mother cells which by meiotic division form microspores.
Each microspore possesses an outer thick wall exine and inner thin wall intine. Micromeres are boat shaped unwinged.
Female strobilus:
Female or megasporangiate strobili arise in whorls of 2, 3 or 4 in the axis of leaves at teach node. Each female strobilus in an elongated structure pointed at the apex. It consists of central axis with 2 or 4 more pairs of bracts. Bracts are sterile except apical one or two which bear single female flowers in the axil.
Each female flower has a short stalk which at the apex bears an ovule of a megasporangium. Each flower arises in the axil of a fertile bract. The megasporangium or ovule has two integuments, the outer has four basal bracts, inner integument has two bracts fused at the base. Outer integument has four vascular bundles. Inner integument becomes hard at the time of pollination and forms long microphyler tube at the top. Nucleus has mass of sterile tissueover lying embryo sac. Funnel shaped pollen chamber is developed which extends to the embryosac and exposes the neck of the archegonium, hence the pollen grains come in contact with archegonium during pollination.
Megasporogenesis:
The ovule in young stage consists of nucellus in the centre surrounded by two layered envelope. From nucellus tissue an archegonial cell gets differentiated which is hypodermal in orgin. The archegonial cell divides periclimically and cuts off several parictal cells and megaspore mother cell, which divides meiotically to form a linear of T shaped tetrad of megaspores which are haploid.
Gametophytic Phase:
Microspores and megaspores on development give rise to male and female gametophytes.
Male Gametophyte:
Microspore is the unit of male gametophyte. Soon after the formation of microspore in microsporangium the nucleus of microspore undergoes a divsion and form a prothallial cell which is separated by a wall. By second division a prothallial nucleus is formed which is cut off from rest of spore i.e. antheridial initial, which divides to form a tumbe cell and a generative cell. Generative cell divides to form the nuclei of stalk cell and body cell. Body cell further divides and gives rise to two nuclei which are alike in size and appearance and are known as male gametes. At shedding stage the exien is thrown off and pollen tube is foremed at once.
Female Gametophyte:
Megaspore is the unit of female gametophyte. The megaspore undergoes free nuclear divisons to from 255 to 500 nuclei. The cell wall formation starts due to which the gametophyte (female) becomes a cellular structure. The female gametophyte or prothallus bears upper reproductive region, middle storage region and basal haustorial region.
The archegonium develops from single superficial cell at the micropyler end of female gametophyte. Each archegonium is elongated with long massive neck, the cells of which are usually 32. This long neck extends to the funne shaped pollen chamber. There is no wall between egg and ventral canal nucleus. Egg is deeply sunken in the tissue of prothallus.
Pollination:
Pollination is Ephedra is animophilous type. Pollen grains with five nuclei and carried by wind to female gametophyte. Microspores lodged in by a pollination drop from where they are sucked in by pollihation drop into pollen chamber. Pollen grains germinate within few hours or their entery into the pollen chamber. The exine ruptures and a pollen tube is formed.
Pollination is Ephedra is animophilous type. Pollen grains with five nuclei and carried by wind to female gametophyte. Microspores lodged in by a pollination drop from where they are sucked in by pollihation drop into pollen chamber. Pollen grains germinate within few hours or their entery into the pollen chamber. The exine ruptures and a pollen tube is formed.
Fertilization: The pollen tube forces its way by the neck of archegonium and burst apically. The tube nucleus, stalk cell and two male nuclei are released into cytoplasm of mature egg. The egg at the time of fertilization is surrounded by cytoplasmic sheath. Male nucleus fuses with egg nucleus and an oospore or zygote is formed which is diploid in nature (2x).
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