[Photoperiodic induction of monospore-development in Porphyra tenera KJELLM. (Rhodophyta-Bangiophyceae)].

The induction of monospore-development in the Conchocelis stage of Porphyra tenera KJELLM. was investigated. 1. Experiments with light-breaks during the dark-periods indicate the decisive role of a photoperiodic control. 2. The critical daylength is approximately 10 hr. Daily light periods longer than 10 hrs inhibit the formation of monospores. 3. Changes in temperature did not induce monospore formation. However, temperature influences the duration of time from photoperiodic induction until the appearance of monospores. 4. By experiments with light-interruption in the dark period the effectiveness of different wavelengths was tested. A strong effect is exerted by wavelengths of 674 nm and 446 nm, and a lesser effect by wavelengths of 674 nm, 553 nm and 431 nm. 5. Light-break experiments with red and far-red light indicate the participation of phytochrome in this photoperiodic control.