a haploid spore, usually smaller than a megaspore of the same plant, which gives rise to a male gametophyte: found in all seed plants, where it is an immature pollen grain, and in many lower vascular plants
"microspore." YourDictionary, n.d. Web. 05 December 2018. <https://www.yourdictionary.com/microspore>.
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One of the two types of haploid spores produced by a heterosporous plant. Microspores develop into male gametophytes and are usually smaller than megaspores. In angiosperms, the microspore develops into the pollen grain.
Germination of the microspore begins before it leaves the pollen-sac. In very few cases has anything representing prothallial development been observed; generally a small cell (the antheridial or generative cell) is cut off, leaving a larger tube-cell.
Microspore spherical or oval, with or without a bladder-like extension of the exine, containing a prothallus of two or more cells, one of which produces two non-motile or motile male cells.
The nucleus of the microspore divides and gives rise to a small cell within the large cell, a second small cell is then produced; this is the structure of the ripe pollen-grain in some conifers (Taxus, &c.).
Three small cells occur inside the cavity of the microspore; two of them collapse and the third divides into two, forming a stalk-cell and a larger body-cell.