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Heterosporous plants that produced microspores in microsporangia and megaspores in separate megasporangia evolved independently in several plant groups during the
Devonian period. Fossils of these plants show that they produced endosporic gametophytes, meaning that their gametophytes were not
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386:. Each anther lobe develops two pollen sacs, so each anther has four pollen sacs. Development of pollen sacs begins with the differentiation of
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Bateman, R.M.; Dimichele, W.A. (1994). "Heterospory - the most iterative key innovation in the evolutionary history of the plant kingdom".
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free-living as in bryophytes but developed within the spores, as in modern heterosporic vascular plants.
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Sporangia that produce spores that give rise to male gametophytes
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divisions to form concentric layers of pollen sac wall.
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that contains the pollen) consists of actively dividing
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The wall layers from periphery to center consist of:
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Stewart, W.N.; Rothwell, Gar W. (26 February 1993).
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may be too technical for most readers to understand
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503:(2 ed.). Cambridge University Press.
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98:, without removing the technical details.
438:. The tapetal cells may be uni-, bi- or
398:division to give a subepidermal primary
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426:endothecium
404:sporogenous
364:angiosperms
335:. They are
333:angiosperms
306:gymnosperms
292:seed plants
276:microspores
525:Categories
451:References
408:anticlinal
396:periclinal
392:hypodermal
325:gymnosperm
310:angiosperm
286:that have
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176:newspapers
50:improve it
444:cytoplasm
419:epidermis
380:epidermis
56:talk page
486:29709953
400:parietal
436:tapetum
353:mitosis
345:meiosis
337:diploid
329:anthers
321:meiosis
313:anthers
190:scholar
90:Please
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372:stamen
368:anther
301:Azolla
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304:. In
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