Comparative development of the spermatozoids of cycads andGinkgo biloba

Cycads andGinkgo biloba are the only extant seed plants that produce flagellated male gametes. Superficially, the cells of both are similar in structure and function. In both the motile organelles arise from multicentriolar bodies, the blepharoplasts, and, in both forms, these give rise to a complex fibrous band, the multilayered structure (MLS), which bears numerous flagella. Generally speaking, these structures are much alike in cycads andGinkgo. However, there are marked differences in details of their development, particularly in the presence of a “nucellar beak” inGinkgo.