21. As it signals the beginning of the breeding season, photoperiod may often signal its end. 22. However, photoperiod only predicts overwintering in areas where day length effects the maturation of milkweeds. 23. Pinyon jays are stimulated by increased photoperiod length and begin breeding in January or early February. 24. Manipulating photoperiod can alter spawning time by over four months and is cheap and straightforward to achieve. 25. These behavioral photoperiod changes in male canaries are caused by changes in the song center of the brain. 26. Photoperiod and temperature treatments after grafting, however, had considerable effect on scion activity and total growth.27. Is it photoperiod , age, temperature, a combination of these factors, or none of these? 28. Hormones such as BAP and paclobutrazol can also be used to completely arrest vertical growth in photoperiod plants. 29. Cannabis grown is induced into flowering by decreasing its photoperiod to at least 10 hours of darkness per day. 30. The length of the dormancy appears to depend on environmental factors, with the most likely zeitgeber being photoperiod .
