Semigamy is an abnormal type of fertilization where syngamy, the union of the sperm and the egg, occurs but synkaryon formation, fusion of their nuclei, does not. Initially semigamy was reported in recurrently apomictic species in which there is a failure of synkaryon formation, and the sporophyte arises from a 2n female gamete. Nonrecurrent semigamy has been reported in Gossypium. In mutant Gossypium that undergo semigamous reproduction both gametes are haploid, and the sperm nucleus takes part in development of the sporophyte. Progeny families include normal hybrid plants as well as maternal and paternal haploids. In addition, progeny can include chimeras with haploid maternal and paternal, and/or hybrid tetraploid tissue. It was suggested that polyspermy might be involved in chimeras with hybrid sectors, but cytological investigations were not reported. It has been proposed semigamy resulted from a dominant allele that conferred facultative semigamous reproduction or that Se is incompletely dominant, and that it is expressed sporophytically in both parents. Expressivity of semigamous reproduction may also be environmentally influenced. Given the unusual effects of the Semigamy mutation and the uncertainties regarding specific cytological mechanisms involved, a cytological investigation of this mutant was conducted, with emphasis on fertilization and early embryogenesis.