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An in-depth exploration of gymnosperms, a group of seed plants whose seeds are not enclosed by an ovary. Various representative groups, including cycads, ginkgo, gnetophyta, and coniferophyta. Each group is discussed in detail, highlighting their characteristics, distribution, and economic importance.
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I. Gymnosperms ("naked" seed plants: not enclosed by an ovary) A. Representative Groups
(3) Each ovule contains a megasporangium embedded in nutritive tissue (nucellus) (4) Each ovule or megasporangium will eventually form a female gametophyte bearing two or more archegonia and is destined to be a seed; two ovules would ultimately result in two seeds (5) Seeds will eventually develop on the shelf-like scales of a female cone (not enclosed) (6) Each ovule, or immature seed, consists of megasporangium which contains a reproductive cell (diploid megaspore mother cell) that undergoes meiosis to produce four large haploid megaspores; the three nearest the micropyle degenerate leaving one which will form an immature female gametophyte b) Also in the Spring, smaller staminate or pollen cones appear containing microsporangium; short- lived and composed of soft tissue which breaks apart soon after pollen formation. (1) Pollen cones are generally produced on the lower branches; clusters of 30-70 cones (2) Sporophylls of the pollen cone (leaf like structures bearing microsporangium) have two microsporangia at their base containing numerous diploid microspore mother cells