CONTRIBUTION TO CYTOLOGY AND DEVELOPMENT OF SIPHONACEOUS GREEN ALGA DERBESIA MARINA

This paper deals primarily with spore formation of Derbesia marina. In an apical zone of the sporangium 15-40 rounded nuclei undergo meiosis. At this stage 8 pairs of chromosomes are observed. After meiosis the cytoplasm of the sporangium is separated from the thallus by the well-known double cell wall. Only one of the daughter nuclei, resulting from each meiotic division, proceeds towards final spore formation. These primary spore nuclei enlarge up to 3 times the diameters of the meiotic prophase nuclei. The remaining nuclei abort. Prior to formation of the spore membranes the ring of the flagellar bases (blepharoplasts) appear on the border of a depression formed on one side of the nucleus. This is followed by a mitotic division, in which long chromosomes are attached with a large spindle. Further mitotic divisions result in multinucleate spores, which are then delimited by the developing spore walls. The details of spore formation in Derbesia tenuissima are similar to those outlined for Derbesia marina. Investigations on cytology and development of the gametophyte produced results similar to those of previous authors studying Halicystis ovalis and Halicystis parvula. Unpublished electron micrographes of the male gamete of Derbesia marina suggest that the posterior bristle-like process contains remnants of the spindle fibres of the preceeding nuclear division. A further cytological investigation on an isolate of Derbesia marina, which lacks the Halicystis generation (Kornmann 1966), has shown this sporophyte to be haploid. Spore formation in the isolate does not involve meiosis. The differences in spore formation between Derbesia marina and Derbesia lamourouxii (Davis 1908) are discussed and the formation of the ring of the flagellar bases compared with that of Oedogonium (Kretschmer 1930). © 1969 Biologischen Anstalt Helgoland.