Sori formation inLaminaria japonica was studied from the ecological and physiological point of view. Cutting through the medulla ofLaminaria japonica improved the formation of sori. Sori formation under different water temperature

photoperiod

and light intensity was investigated and total nitrogen and reducible sugar content determined. The result showed that sori ofL. japonica can be formed in 1–22°C water in Dalian. No sori were found in water over 23°C. High temperature inhibits the formation of sori

but low temperature has no effect. Apparently

light intensity affects the formation of sori

but photoperiod does not. In shallow waterL. japonica grows slower but stores dry material faster and forms sori rapidly. In deeper water it grows faster in length but stores dry material slower and the sori formation is slow. Analysis of dry material shows that during sori formation the water content decreases but total nitrogen and total reducible sugar increase. Only when the storage of sugar reaches a certain level can sori begin to form. Cutting through the medulla interrupts the passage of nutrients to the growth area. Storage of carbohydrates and nitrogen is the main factor affecting sori formation.