Germination ofLycopus europaeusL. in response to fluctuating temperatures and light

Germination of Lycopus europaeus depends absolutely on both a diurnal temperature fluctuation and light. Studies of the parameters and interactions of these two environmental factors produced no evidence of critical temperatures for germination, which could occur over a wide range of different temperature combinations provided the magnitude of the diurnal fluctuation exceeded 7 °C. Successive temperature cycles produced a cumulative effect, and both a temperature rise and a fall were essential for the completion of processes leading to germination. The time interval between these two temperature changes was criticial, showing both a minimum and a maximum which varied with temperature conditions. Light irradiation was essential at some point in the cycles, though it was not tied to any particular phase; brief light breaks at repeated intervals were as effective as much longer periods of continuous illumination