Pine gametophyte (outside) surrounding the embryo (inside). A gametophyte is the haploid multicellular stage in the alternation of generations life cycle of plants and algae. It develops from a spore by mitotic cell division. Spores are the products of meiosis in sporophytes.Gametophytes produce haploid gametes by mitosis.he fusion of male and female gametes produces a diploid zygote, which develops by repeated mitotic cell divisions into a multicellular sporophyte. In bryophytes (mosses, liverworts, and hornworts), the gametophyte represents the longer lived, nutritionally independent and more visible stage of the life cycle.