Abstract
Investigation of reproduction in Saccorhiza dermatodea reveals that its zoospores possess an eyespot in the chloroplast, and that its gametophytes are monoecious with antheridia formed in catenate series on specialized laterals. These features are interpreted as indicating primitiveness in the order Laminariales. Gametogenesis occurs only at temperatures below 14°C under short-day conditions. This is the first report of a daylength response in gametophytes of Laminariales.