megasporangium
Quick Summary
A megasporangium is a plant structure that produces megaspores, which develop into female gametophytes. In angiosperms, this megasporangium is called the nucellus. It is typically enclosed by one or two integuments, leaving a small opening called the micropyle. Within the nucellus, a megasporocyte undergoes meiosis to form a tetrad of megaspores, with usually only one surviving to enlarge and develop into the megagametophyte, also known as the embryo sac. This embryo sac contains eight nuclei and produces the female gametes, or eggs. In seed plants, the megagametophyte is a parasite on the sporophyte.12
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plantHeterosporous life historiesMegasporangia (female sporangia) produce megasporocytes (megameiocytes) that yield megaspores. The sporangia may be borne in specialized structures such as sori in ferns, cones (strobili) in some pteridophytes and most gymnosperms, or flowers in angiosperms. The leaflike structures bearing microsporangia and megasporangia are called, respectively, microsporophylls…
Read MoreMegasporangia (female sporangia) produce megasporocytes (megameiocytes) that yield megaspores. The sporangia may be borne in specialized structures such as sori in ferns, cones (strobili) in some pteridophytes and most gymnosperms, or flowers in angiosperms. The leaflike structures bearing microsporangia and megasporangia are called, respectively, microsporophylls…
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plant reproductive systemLycopsids…strobili bear megasporophylls that contain megasporangia, which will produce megaspores, and microsporophylls that contain microsporangia, which will yield microspores. Although the evolutionary origin of two kinds of spores (dimorphism) is unknown, the development of megaspores in living plants suggests that differences in nutrition in the two kinds of sporangia are…
Read More…strobili bear megasporophylls that contain megasporangia, which will produce megaspores, and microsporophylls that contain microsporangia, which will yield microspores. Although the evolutionary origin of two kinds of spores (dimorphism) is unknown, the development of megaspores in living plants suggests that differences in nutrition in the two kinds of sporangia are…
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gymnospermGeneral featuresWithin each megasporangium, a single cell undergoes meiotic division to produce four haploid megaspores, three of which typically degenerate. The remaining megaspore undergoes mitosis to form the female gametophyte. As the number of free nuclei multiplies, the megasporangium and megaspore wall expand. At this stage the ovule…
Read MoreWithin each megasporangium, a single cell undergoes meiotic division to produce four haploid megaspores, three of which typically degenerate. The remaining megaspore undergoes mitosis to form the female gametophyte. As the number of free nuclei multiplies, the megasporangium and megaspore wall expand. At this stage the ovule…
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gnetophyteReproductive structures and functionMegasporangiate, or seed-producing, strobili (female cones) consist of oppositely paired bracts in the axils of which are fertile shoots consisting of paired bracteoles enclosing an ovule—the forerunner of a seed. The ovule consists of a delicate inner envelope, called an integument, that encloses a tissue…
Read MoreMegasporangiate, or seed-producing, strobili (female cones) consist of oppositely paired bracts in the axils of which are fertile shoots consisting of paired bracteoles enclosing an ovule—the forerunner of a seed. The ovule consists of a delicate inner envelope, called an integument, that encloses a tissue…
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