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heterosporythe formation of more than one sort of SPORE, usually MICROSPORES and MEGASPORES in ferns and seed plants, giving rise to distinct male and female GAMETOPHYTE generations. The terms mega-and microspore were first used in connection with PTERIDOPHYTES where differences in spore size occur. Later, because of how the structures are formed, these terms were used in reference to seed plants where such size differences are rarer. Here the microspore is the pollen, and the megaspore is the cell which gives rise to the EMBRYO SAC.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005