[Culture experiments on life cycle, nuclear phases, and sexuality of the brown alga Ectocarpus siliculosus].

The life cycle of Ectocarpus siliculosus from Naples (Italy) was investigated, using well defined cultured material. Gametophytes and sporophytes differ morphologically and functionally. The gametophytes are dioecious, with genotypic determination of their sex. Sporophytes exist in the haploid, diploid and tetraploid phase. All sporophytes can form unilocular sporangia. In tetraploid and diploid sporophytes the formation of unilocular sporangia is connected with meiosis. Certain motile cells of haploid plants may spontaneously give rise to diploid or tetraploid sporophytes which are homozygous. Gametophytes can only be formed together with sporophytes form the swarmers of unilocular sporangia (heteroblasty). Meiosis in tetraploid sporophytes resulted in diploid gametophytes, the gametes of which fused with haploid female gametes. All observed nuclear phases and growth forms are connected with each other by meiosis, heteroblasty, fusion of gametes and spontaneous increase in chromosome number.