Sporangia that produce spores that give rise to male gametophytes
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A microsporangium (pl. microsporangia) is a sporangium that produces microspores that give rise to male gametophytes when they germinate. Microsporangia occur in all vascular plants that have heterosporic life cycles, such as seed plants, spike mosses and the aquatic fern genus Azolla. In gymnosperms and angiosperm anthers, the microsporangia produce microsporocytes, the microspore mother cells, which then produce four microspores through the process of meiosis. Microsporocytes are produced in the microsporangia of gymnosperm cones and the anthers of angiosperms. They are diploid microspore mother-cells, which then produce four haploid microspores by meiosis. These become pollen grains, within which the microspores divide twice by mitosis to produce a very simple gametophyte.
Heterosporous plants that produced microspores in microsporangia and megaspores in separate megasporangia evolved independently in several plant groups during the Devonian period. [1] Fossils of these plants show that they produced endosporic gametophytes, meaning that their gametophytes were not free-living as in bryophytes but developed within the spores, as in modern heterosporic vascular plants.[2]: 280
In angiosperms, a very young anther (the part of the stamen that contains the pollen) consists of actively dividing meristematic cells surrounded by a layer of epidermis. It then becomes two-lobed. Each anther lobe develops two pollen sacs, so each anther has four pollen sacs. Development of pollen sacs begins with the differentiation of archesporial cells in the hypodermal region below epidermis at four corners of the young anther. The archesporial cells divide by periclinal division to give a subepidermal primary parietal layer and a primary sporogenous layer. The cells of the primary parietal layer divide by successive periclinal and anticlinal divisions to form concentric layers of pollen sac wall.[citation needed]
The wall layers from periphery to center consist of:[clarification needed]
A single layer of epidermis, which becomes stretched and shrivels off at maturity
A single layer of endothecium. The cells of endothecium have fibrous thickenings.
One to three middle layers. Cells of these layers generally disintegrate in the mature anther
A single layer of tapetum. The tapetal cells may be uni-, bi- or multinucleate and possess dense cytoplasm. The cells of the primary sporogenous layer divide further and give rise to diploid sporogenous tissue.
^Bateman, R.M.; Dimichele, W.A. (1994). "Heterospory - the most iterative key innovation in the evolutionary history of the plant kingdom". Biological Reviews of the Cambridge Philosophical Society. 69 (3–4): 315–417. doi:10.1111/j.1469-185X.1994.tb01276.x. S2CID 29709953.
^Stewart, W.N.; Rothwell, Gar W. (26 February 1993). Paleobotany and the evolution of plants (2 ed.). Cambridge University Press. ISBN 0-521-38294-7.
A microsporangium (pl. microsporangia) is a sporangium that produces microspores that give rise to male gametophytes when they germinate. Microsporangia...
side of the anther. A pollen grain develops from a microspore in the microsporangium and contains the male gametophyte. The size of anthers differs greatly...
which provides nutrition for growing spores . The innermost wall of microsporangium Tapetum lucidum, a reflective tissue layer associated with the retina...
producing large spores that contain the female gametophytes. Compare microsporangium. megaspore the larger of two kinds of spores produced by a heterosporous...
microsporangia, or pollen sacs, of the anthers on the stamens. Each microsporangium contains diploid microspore mother cells, or microsporocytes. Each...
germination of the pollen grain may begin even before it leaves the microsporangium, with the generative cell forming the two sperm cells. Except in the...
separate sporangia, either a megasporangium that produces megaspores or a microsporangium that produces microspores. In flowering plants, these sporangia occur...
produces one or more microsporangia. Microspores develop within the microsporangium by meiosis. In a willow (like all seed plants) the zygote first develops...
spores (microspores) are extremely small and are produced inside each microsporangium. Microspores tend to adhere in clumps called massulae. Female sporocarps...
parallel to these developments, the other kind of sporangium, the microsporangium, produces microspores. A tiny gametophyte develops inside the wall...
fed on the pollen of strobili, moving between the scales from one microsporangium to another. Metropatoridae Metropator Archaemiopteridae Guthorl, 1939...
take several generations of selection to produce a homozygous line. Microsporangium Spore Megaspore Evert, Ray (2013). Biology of Plants. New York: Peter...
the ovary, and an expanded tip, the stigma. Within the stamen, the microsporangium forms grains of pollen, surrounded by a protective microspore, which...