Sequence of Sexual and Asexual Phases in Antithamnion spirographidis Schiffner

Abstract

THE plants of many Florideae bear either sexual reproductive organs or tetrasporangia, and there is a reasonable amount of cytological evidence in support of the generalization that plants bearing tetrasporangia have twice as many chromosomes as those bearing sexual organs, meiosis occurring in the tetrasporangium. On the other hand, there is surprisingly little evidence from controlled experiments to show that the plants which develop from carpospores bear tetrasporangia and that those which grow from tetraspores bear sexual organs. Lewis¹ allowed either tetraspores or carpospores, whichever were available, to become attached to oyster shells in the laboratory and he then submerged the shells in the sea. From subsequent examination of the shells, he concluded that tetraspore-bearing plants of Polysiphonia violacea had developed from carpospores and sexual plants from tetraspores of Griffithsia bornetiana and Dasya elegans. The numbers of plants grown were Polysiphonia violacea (6), Griffithsia bornetiana (60) and Dasya elegans (149). Dammann² obtained small plants bearing tetrasporangia of Halarachnion ligulatum from carpospores, although tetrasporophy tes of this species are unknown in the sea. Hassinger's³ experiments with Callithamnion collymbosum were more extensive; but the results were complicated by the fact that in this species some diploid plants bear branches with male and female reproductive organs as well as tetrasporangia.