Experiments were made to compare the stimulating effectiveness of vertically and horizontally polarized lights and non-polarized lights of equal intensity upon phototropic movements of the beetle Tetraopes tetraopthalmus; and to compare the effectiveness of two light beams polarized at right angles to one another upon phototropic orientation of the land isopod Cylisticus convexus. Tetraopes is positively, and Cylisticus, negatively phototropic. Tests were also made of the intensities of horizontally and of vertically polarized light required to inhibit stereotropism in larvæ of Tenebrio. Under the conditions of the tests, no certain qualitative effect connected with polarization could be detected.