Motor Responses to Polarized Light and Gravity Sensing in <i>Euglena gracilis</i>*^†

Abstract

SYNOPSIS. Euglena gracilis strain Z has a motor response which results in orientation with respect to the polarization of a light stimulus. Cells swim preferentially in a direction perpendicular to the plane of polarization of the stimulus. If 2 polarized stimuli are given from opposite directions, the preferred direction is, under certain circumstances, at right angles to the directions of both stimuli. Euglena also preferentially assumes an orientation that is at right angles to the force of gravity. The relationships between these responses and phototactic movements oriented with respect to the direction of the stimulus are discussed.