GENERATIONS, ALTERNATION OF. The alternating phases—particularly the sexual and asexual changes—which take place in successive generations of animals and plants. In plants gamotophytes alternate with sporophytes, the latter being asexual, this phenomenon being found in all plants except certain lower forms in which sporophytes are absent. It is well exemplified in mosses and ferns. Among animals the alternation of generations takes several forms. The broods of butterflies and moths differ in colour at certain seasons. In flat worms or trematodes, and insects such as Phylloxera, heterogenesis—the succession of a parthenogetically produced generation by a dioecious—takes place.
See REPRODUCTION, BRYOPHYTA, PTERIDOPHYTA, GYMNOSPERMS, PROTOZOA, COELENTERATA, PLATYHELMINTHES, ANNELIDA.