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Microspores are land plant spores that develop into male gametophytes, whereas megaspores develop into female gametophytes. The male gametophyte gives rise to sperm cells, which are used for fertilization of an egg cell to form a zygote. Microspores 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. Microspores are haploid, and are produced from diploid microsporocytes by meiosis. ==Seedless vascular plants== Microsporophylls bear microsporangia containing many microsporocytes that undergo meiosis, producing tiny microspores. Each microspore may become a male gametophyte consisting of a somewhat spherical antheridium within the microspore wall. Either 128 or 256 sperm cells with flagella are produced in each antheridium. In the ferns, the only heterosporous plants are aquatic or semi-aquatic, including the genera ''Marsilea'',''Regnellidium'', ''Pilularia'', ''Salvinia'', and ''Azolla''. This condition is also known in the lycopod genus ''Selaginella'' and in the quillwort genus ''Isoëtes''. Types of seedless vascular plants: * Ferns * Spikemosses * Quillworts 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「microspore」の詳細全文を読む スポンサード リンク
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