Germination of the Light‐sensitive Seeds of Cucumis Angur1a and Rumex Obtusifolius: Effects of Temperature

Summary The effect of temperature and exposure to far red light were compared using positively photoblastic seeds of Cucumis and negatively photoblastic seeds of Rumex. Short exposure of Cucumis seeds to 45°C was without effect but exposure at 0°C for 1 to 3 h promoted subsequent germination in white light at a constant temperature of 25°C. In contrast, white light alternating temperatures 25/10 and 25/5°C fully counteracted the inhibitory effect of light on germination of Cucumis seeds. The temperature pairs 15/35, 20/35, and 25/35°C were tested with both Rumex (in darkness) and Cucumis (in light). Seeds of both species had their germination strongly promoted by the 15/35°C pair. The pair 25/35°C had a promotive effect in Rumex and no effect in Cucumis, while the pair 20/35°C was very effective for Rumex but much less so for Cucumis. In experiments in which the alternating pair 25/5°C was combined with far red (followed by darkness and white light), Rumex and Cucumis seeds behaved similarly. With both, when far red was given during the 5°C period followed by light or darkness at 25°C germination was promoted (but the inhibitory effect was completely reversed only where far red was followed by white light). When far red was given at 25°C followed by white light or darkness during the 5°C period germination was not promoted. Thus, both positively and negatively photoblastic seeds show the same behaviour in relation to light and temperature when exposed to far red.