Tropistic responses of zygotes of the Fucaceae to polarized light

Abstract

The following picture is drawn from experiments on two members of the Fucaceae, Fucus furcatus and Pelvetia fastigiata: 1. 1. In their “polarotropic” response to unidirectional illumination with plane polarized visible light, the zygotes tend to germinate in the plane of vibration, and “subequatorially” (from 90 ° to 135 ° away from the source). (Fig. 1.) Up to half the embryos so produced may be bipolar forms. 2. 2. The tropistic response to similar unpolarized light is dual. Under some partially defined conditions it is subequatorial; under others, directly away from the source. 3. 3. The polarotropic response and the subequatorial response to unpolarized light fade out over the same intensity range (Fig. 4). 4. 4. The polarotropic action spectra (Fig. 3) belong to the phototropic group of spectra as found with other organisms (Table VI). 5. 5. It is concluded that in all three tropistic responses to light, growth tends to occur where certain photoreceptor molecules absorb the least light. 6. 6. It is suggested that under unpolarized illumination the subequatorial and peripheral photoreceptors absorb least light primarily because they are by-passed by the cell's focusing action (Fig. 5), while under polarized illumination the subequatorial photoreceptors in the vibration plane absorb least light because they are periclinally oriented (Fig. 6).