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Definition: 1. A usually one-celled reproductive body that can grow into a new organism without uniting with another cell. Spores are haploid (having only a single set of chromosomes). Fungi, algae, seedless plants, and certain protozoans reproduce asexually by spores. Plant spores that are dispersed by the wind have walls containing sporopollenin. 2. A similar one-celled body in seed-bearing plants; the macrospore or microspore. The macrospore of seed-bearing plants develops into a female gametophyte or megagametophyte, which is contained within the ovule and eventually produces the egg cells. (The megagametophyte is also called the embryo sac in angiosperms.) The microspore of seed-bearing plants develops into the male microgametophyte or pollen grain.
Source: The American Heritage Science Dictionary. Boston: Houghton Mifflin, 2005. Credo Reference. Web. 17 August 2012.