Microsporangium
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Microsporangia
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microsporophylls
with microsporangiaA microsporangium (pl. microsporangia) is a
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
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.
References
- S2CID 29709953.
- ISBN 0-521-38294-7.