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The larger of two spore types of certain protozoans or fungi.
Synonym(s): megalospore, megaspore
[macro- + G. sporos, seed]
Farlex Partner Medical Dictionary © Farlex 2012




the larger of two types of SPORES produced by many ferns and seed plants. The megaspore gives rise to a female GAMETOPHYTE in ferns and in seed plants, and in flowering plants becomes the EMBRYO SAC. Compare MICROSPORE.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
The functional megaspore undergoes three successive mitoses resulting in the formation of an 8- nucleate embryo sac of the Polygonum type.
Megaspores were considered to have germinated when an apical globular green structure with a crown of rhizoids was observed (Wunder et al., 2009).
This single haploid megaspore undergoes three consecutive mitotic divisions to produce two, then four, and finally eight haploid nuclei within a single cell in the ovule.
megaspore A haploid spore (N) that will develop into a female gametophyte.
Twenty-five megaspores were placed in each glass vial (4.5 x 10 cm) with 25 mL of the culture medium, with four repetitions for each treatment.
Sporangium wall pigmented with brown; megaspores with short ridges, wart-like projections (tuberculate to papillate) or almost smooth; plant terrestrial or amphibious in wet clay soils or on rock outcrops.
However, not all seed-fertile triploid Musa accessions generate a high frequency of 2n megaspores (Ortiz, 1995).
The inner integument initiates first, and then the outer integument develops into a small protuberance at the megaspore mother cell stage.
megasporocyte: Megaspore mother cell; this diploid cell undergoes meiosis to produce four haploid megaspores in the ovules of angiosperms.
and ultrastructure of megaspores and microspores of Isoetes savatieri
However, in most ovules, shortly after megasporogenesis from one to seven nucellar cells in the area adjacent to the functional megaspore enlarged and their nuclei became prominent.