Cultivation of the red sea-weed Porphyra tenera was started in Japan several centuries ago. It is now the largest industrial cultivation of any marine products. Despite this fact, more knowledge of Porphyra is needed for improving methods of cultivation-to bring them under a control comparable to that achieved in land agriculture. In this paper, the results of ecological and physiologicav studies on P. tenera are contained.
Environmental characteristics both on Matsushima Bay (Miyagi pref.) and Matsukawa-ura inlet (Fukushima pref.), where the cultural industries are practising, were investigated. Several factors affecting the production of Porphyra were clarified from the results of survey. These results are summarized in Figs. 1-18, and Tables 1-4. The relation between the growth of Porphyra thalli and the environmental factors were also examined (Figs. 19-30, and Tables 5-7).
Experimental results on mineral nutrition of P. tenera are shown m Figs. 31-35, and Tables 8-12. Axenic culture of P. tenera was obtained by the "dip and drag" technique in an agarized medium containing antibiotics. Then, vitamins requirements and effects of plant hormones were examined. The results are indicated in Tables 13-14. In axenic culture of P. tenera needs vitamin B12 for growth.
III. Artificial management of the life-cycle.
The complete life-cycle of P. tenera was obtained in vitro. Chemically defined media or enriched sea-water permit good growth of these unialgal (not bacteria-free) cultures. Under suitable light and temperature, the entire life-cycle is completed in 5-6 months. Both the Conchocelis and the thallus phases grow out of season. The Conchocelis phase grows well free in liquid media; a calcareous substrate is unnecessary. Monosporangia formation and release of fertile monospores are induced by short-day conditions (8-11 hours daily); monosporangia and germinating monospores develop after 1-2 months from the inoculation of the Conchocelis filaments (Table 16). A daily photoperiod of 13 hours inhibits growth of young thalli. Carpospores production are induced by long-day conditions (Table 18). The experiments show that the length of the photoperiod has remarkable effects on the Conchocelis and leafythallus phases of P. tenera. The photoperiod governs, besides growth, the formation of the spores producing the next phase of the life-cycle.