Nutations of sunflower seedlings on tilted clinostats.

The kinetics of hypocotyl nutations in Helianthus annuus L. were measured on plants which were rotated on clinostats with axes of rotation inclined at various angles, alpha, away from the vertical. The g-force component acting in the direction of the plant axis was taken as g cos alpha. The average period and average amplitude of nutation were constant for all such axially directed g-forces between 1.0 and 0.2 g (vertical to about 80 degrees inclination). On the horizontal clinostat (90 degrees inclination) nutation was neither initiated nor sustained. The g-force just sufficient fully to activate nutational oscillations should be sought in the range of the g-force parameter, 0 < g < 0.2.