21. This sensitivity to day length is termed photoperiodism. 22. Natural molting is stimulated by shortening day lengths combined with stress ( of any kind ). 23. Lunar cycle, day length , and possibly chemical signalling. 24. When growth elongation is complete, day length is reduced to 8 hours using a blackout curtain. 25. Day length and temperature are the two triggers for color change and leaf loss, he said.26. These onions are less fussy about day length and will reliably bulb in the North or South. 27. Spring leaf budding by the European beech is triggered by a combination of day length and temperature. 28. The winter moult is instigated not by a change in temperature but by a change in day length . 29. Breeding takes place when the water temperature falls to about and the day length is at its minimum. 30. Day length doesn't vary so much.
