COSMOS, a- genus of tropical American herbs of the family Compositae, comprising about 20 species chiefly Mexican. They are late-flowering annuals or perennials with long-stalked showy flower-heads borne singly or in clusters. Several species are in cultivation as ornamental annuals. Of these the best known is the common cosmos (C. bipinnatus), 7 f t. to o ft. high, extensively grown in gardens. It has a smoothish stem bearing much-cut, narrowly-lobed leaves and flower-heads with a yellow centre (disk) encircled by pink, crimson or white rays. The plant thrives best in sandy, not too rich, soil and germinates readily; in the northeastern United States the best results are attained by sowing the seed indoors in April and transplanting when danger of frost is past.