Answer: nutations

AnswerCrossword Clue
NUTATIONSPlant-growth cycles
nutationsact or instance of nodding one's head, esp. involuntarily or spasmodically
nutationsspontaneous movements of plant parts during growth
nutationsthe periodic oscillation observed in the precession of the earth's axis and the precession of the equinoxes
nutationsNUTATION, a nodding (the action of a nod)