RELATION BETWEEN ELECTRICAL AND CURVATURE RESPONSES IN THE AVENA COLEOPTILE TO MECHANICAL STIMULI

When an Avena coleoptile is placed in the horizontal position, it grows away from the center of the earth. This bending is the result of unequal rates of elongation of the upper and lower sides of the plant, and is commonly explained on the basis of the familiar Cholodny-Went theory of plant curvature responses (3, 19). The early work of Bose (2) and, in recent years, the experiments of Brauner (4, 5, 6) and Brauner and Amlong (7) have demonstrated that the under side of various plant stems becomes electropositive to the upper side when these stems are placed in the horizontal position. Wilks and Lund (20) have performed preliminary experiments which show that the under side of a horizontally placed Avena coleoptile also becomes positive to the upper side. It has been conclusively confirmed (17), not only that the under side of the coleoptile becomes positive to the upper side, but that the entire internal electrical correlation pattern (12) changes when the position of the living coleoptile is changed from vertical to horizontal. Frequent observations have shown that mechanical stimulation of a segment of living tissue causes that segment to become electronegative to unstimulated regions. This has been proved to be the case for the electrically polar growth axis in the Douglas Fir (13), in the root of Allium cepa (14), and Chara vulgaris (8). Certain observations of Bose (1) and Orbeli and Br?cke (15) might be considered exceptions to this phenomenon. The growth response to mechanical stimulus, which was first studied in tendrils is also rather widely distributed in etiolated seedlings and other stems. Stark (18) was able to induce curvature in the Avena coleoptile and other plants by stroking one side of the plant with a cork rod. The stimulated side became the concave side. More extensive references are cited by Stark. The experiments herein reported are intended to show, in a semi-quantitative way, how mechanical stimulation affects the transverse electrical polarity, the growth curvature, and their sequence relationships in the Avena coleoptile while in the upright and in the horizontal positions.