Abstract
Summary The influence of circumnutation and passive stem bending on gravitropism of 9- to 10-d-old lightgrown pea seedlings ( Pisum sativum L.) was studied using time-lapse photography. Plants placed horizontally without regard to circumnutation exhibit erratic movements, but if they are stimulated when in the same phase of the circumnutational cycle these irregularities disappear. In plants turned vertically after a short period of horizontal stimulation, the initial bending is due more to circumnutation than to gravitropism. The initial response to gravity in horizontally placed plants is a downward movement of the stem. The kinematics of this movement suggests it is due both to elastic and plastic passive stem deformation and is not a positive gravireaction. When stems are turned upright after short horizontal stimulation, it takes some time for them to recover and adds an erroneous negative movement to the initial graviresponse curve.
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