ENVIRONMENTAL CONTROL OF GAMETOGENESIS IN LAMINARIA SACCHARINA. IV. IN SITU DEVELOPMENT OF GAMETOPHYTES AND YOUNG SPOROPHYTES1,2

Meiospores of Laminaria saccharina labeled with a fluorescent stain were put into the sea and recovered at frequent intervals. They developed into gametophytes which produced gametes throughout the year. Antheridia were produced earlier than oogonia. Gametogenesis was slowest during the late autumn and early winter. On the basis of nutritional studies and the seasonal distribution of nutrients, it was concluded that the rate of gametogenesis was not due to nutrient deficiency but most likely to light. Production of macroscopic sporophytes appeared to be limited by survival of microscopic sporophytes rather than gametogenesis. Macroscopic sporophytes became evident during the late winter and autumn. The greater light and perhaps higher temperatures of summer were suggested as agents limiting macroscopic sporophyte production during this period.