[The geoelectric reactivity of the inflorescence axes of lupinus polyphyllus]

The relations between the auxin content, the geotropic reactivity and the geoelectric reactivity of the axes of lupine inflorescences of different age were examined. 1. The stems of young inflorescences put in the horizontal position curve up by 80-85° within 8 hours. The zone of curvature extends from the 4th cm down to the 16th cm below the apex. After fertilization of the flowers the stem looses its geotropic reactivity almost completely. 2. It could be shown that a close relation exists between the geotropic reactivity of the different regions of the stem and their ability to produce the geoelectric "after effect" (GEE2). Under the same experimental conditions a potential difference develops in the middle region of the curvature zone of young stalks which is 4 times as high as in older axes which have almost lost their ability to curve geotropically. 3. In young shoots the ability to produce a strong electric "after effect" is confined to the middle and to the upper region of their curvature zone. In its tropistically inactive basal region the GEE2 induced under the same conditions reaches only about 30% of the effect developing in the upper part. 4. The primary geoelectric effect (GEE1) which has to be attributed to the influence of gravity upon preexisting diffusion potentials depends in its extent but little on the geotropic reactivity of the tested region of the axis. The transversal potential difference developing in the horizontal position of the shoot reaches approximately the same magnitude in all regions of young and old stems examined. 5. In order to decide whether the differences observed in the electric reactivity of the tested zones of young and old stems might be related to their auxin content, their growth substance activity was measured with the coleoptile cylinder test. It appeared that the GEE2 can effectively develop only in the regions of the young stem rich in auxin. The GEE1, however, proved to be almost independent of the auxin level in the organ. The possible reasons why this behaviour differs from that of other plants tested are discussed.