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Megaspores are structures that are part of the alternation of generations in many seedless vascular cryptogams, all gymnosperms and all angiosperms. Plants with heterosporous life cycles using microspores and megaspores arose independently in several plant groups during the Devonian period. [ 2 ]
Megaspores, also called macrospores, are a type of spore that is present in heterosporous plants. These plants have two spore types, megaspores and microspores . Generally speaking, the megaspore, or large spore, germinates into a female gametophyte , which produces egg cells .
Microspores: Produced sexually through meiosis, and give rise to a male gametophyte: Pollen in seed plants In plants, microspores, and in some cases megaspores, are formed from all four products of meiosis. Megaspores (macrospores) Produced sexually through meiosis, and give rise to a female gametophyte: Ovule in seed plants
Spores of two distinct sizes (heterospory or anisospory): larger megaspores and smaller microspores. When the two kinds of spore are produced in different kinds of sporangia, these are called megasporangia and microsporangia. A megaspore often (but not always) develops at the expense of the other three cells resulting from meiosis, which abort.
A female pinecone produces the megaspores of this heterosporic plant. A male pinecone produces the microspores of this heterosporic plant. Heterospory is the production of spores of two different sizes and sexes by the sporophytes of land plants. The smaller of these, the microspore, is male and the larger megaspore is female.
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 ...
[7]: 18 These plants produce both microspores and megaspores, which give rise to gametophytes that are functionally male or female, respectively. Most heterosporous plants there are two kinds of sporangia, termed microsporangia and megasporangia.
In organisms that are heterosporous, two types of spores occur: Microsporangia produce male microspores, and megasporangia produce female megaspores. In megasporogenesis, often three of the four spores degenerate after meiosis, whereas in microsporogenesis all four microspores survive.
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