[Studies on the life cycle of the brown alga Ectocarpus siliculosus from Naples, Italy]

Culture experiments and cytological studies were carried out under well-defined conditions. The haploid chromosome number is between 18 and 31. There are two morphological types of plants: the well-branched gametophyte resembling the plants found in nature, and the unbranched sporophytic form which may be haploid or diploid, found only in cultures. Meiosis takes place in the unilocular sporangia on diploid sporophytes. Haploid sporophytes form unilocular sporangia without reduction of the chromosome number. The spores from unilocular sporangia both on diploid and haploid sporophytes give rise to plants with either sporophytic or gamethophytic growth. The gametophytes are homothallic, the gametes forming motile zygotes with four flagella. Parthenogenetic development of gametes exclusively results in the formation of haploid sporophytes. Both the haploid and diploid sporophytes can propagate by means of zoids from plurilocular sporangia. Several observations reported here disagree with the findings of other workers.