TETRADYNAMIA, (tetragyne "four," and dyname "power"), four powers; the name of the 15th class in Linnaeus's Sexual System, consisting of plants with hermaphrodite flowers, having six stamens, four of which are long, and two short; it corresponds to the stiquosa of Ray, and cruciformes of Tournefort. All the species belonging to this class are distinguished by cruciform flowers. It comprehends two orders, gymnosperma, those plants which have naked seeds, being four in number, (except phryma which is monospermous); and angiosperma, which contains those plants the seeds of which are inclosed in a capsule. See BOTANY, p. 430.