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– **Megasporogenesis:**
– Megasporogenesis occurs in gymnosperms and flowering plants.
– The process involves a diploid precursor cell undergoing meiosis to produce four haploid cells.
– Angiosperms exhibit three patterns: monosporic, bisporic, and tetrasporic.
– Monosporic pattern is most common (70% of angiosperms) in economically important plant groups.
– Each pattern results in a single functional megaspore containing different numbers of meiotic nuclei.

– **Megagametogenesis:**
– After megasporogenesis, the megaspore develops into the female gametophyte.
– The process of megagametogenesis varies based on the pattern of megasporogenesis.
– Monosporic pattern leads to the formation of an eight-nucleate cell with specific cell arrangements.
– Different patterns of megasporogenesis result in varying embryo sac structures.
– In some plants like Lilium with a tetrasporic pattern, the endosperm can be 5n upon fertilization.

– **See also:**
– Megasporangium.
Double fertilization.

– **References:**
– A. A. Estrada-Luna et al. discussed apomixis in flowering plants.
– Yadegari and Drews focused on female gametophyte development.
– Raven, Evert, and Eichhorn authored “Biology of Plants.”
– Sargent’s work in 1900 explored fertilization results in angiosperms.

– **Additional Information:**
Megaspore is produced inside the nucellus of the ovule.
– Megasporogenesis leads to the formation of the embryo sac.
– Different plant species exhibit various patterns of megasporogenesis and megagametogenesis.
– The process of megagametogenesis results in the formation of different types of embryo sacs.
– Fertilization of the central cell in the embryo sac leads to endosperm development.

Megaspore (Wikipedia)

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. These are fertilized by sperm produced by the male gametophyte developing from the microspore. Heterosporous plants include seed plants (gymnosperms and flowering plants), water ferns (Salviniales), spikemosses (Selaginellaceae) and quillworts (Isoetaceae).

Microscopic photo of spores (in red) of Selaginella. The large three spores at the top are megaspores whereas the numerous smaller red spores at the bottom are microspores.
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