THE INFLUENCE OF LIGHT ON THE GERMINATION OF SENECIO VULGARIS L.

S ummary Achenes of Senecio vulgaris L. show a strong positive requirement for white or red light to attain maximal germination at 20 °C. The response to light is mediated by the photoreversible photoreceptor phytochrome. The light requirement can also be satisfied by short daily irradiations with red light (660 nm) and far‐red light given at the end of daily red light photoperiods depresses germination to Cedeximately 60%. It is suggested that P fr , the active form of photochrome, once formed, persists for between 8 and 10 h. The interactions between light, KNO 3 and constant temperatures between 0 and 30 °C have also been studied.