The time of flower opening and closure has been observed in twenty species belonging to nine different families. Increasing light initiates opening in some flowers and different species have different thresholds of response. Other species appear to be unaffected by light intensity.
Experiments on the effect of photoperiod on petal movement in Talinum triangulare and Mirabilis jalapa indicate that the photo-fraction affects the period of the rhythm by altering phase-timing. A close correlation is suggested between phase-timing and the automatic self-pollination mechanism in Talinum possibly also in Mirabilis.
Temperature also modifies the period of the rhythm in Tradescantia and Talinum; in the latter, a temperature of 24°C promoted closing.