Investigations of the Geotropic Curvature of the Avena Coleoptile

Abstract

The geotropic presentation time was studied in Avena coleoptiles as a function of the distance from the tip. Curvatures of decapitated plants, allowed to curve in IAA‐solutions, were recorded. Extrapolated values of the presentation times are roughly the same (about 4 min) in coleoptiles from which 1, 3, or 5 mm, respectively, of the tip have been removed by decapitation. Presentation times reported in the literature are generally longer and are stated to increase considerably with the length of the portion of the tip removed by decapitation. No such relationship was found in the present study. The discrepancies can, at least to a large extent, be explained by differences in principles and methods of measurement. The present results are in accord with measurements on the geoelectric effect in coleoptiles.

Aspects on gravity-induced movements in plants

“…Dolk (1936), using the 50 % method described on page 290, got very high values for the presentation time with decreasing distance from the tip: 35 min 5 mm below the tip, n o min 10 mm below it. Using the extrapolated presentation time t p , see page 289, roughly the same t p value is reached at the tip and 5 mm below it (Johnsson, Rengman & Grahm, 1971). A constant t p value is therefore compatible with Grahm's measurements on the constant latency time.…”

“…The absolute threshold time for geotropic response is obviously much lower than the extrapolated presentation time t p . t p can be regarded as an approximate starting time for the more or less logarithmic phase of the stimulusresponse curve (Johnsson, 1971&). In physiological sensory systems the absolute limits are theoretically set by the Brownian movement (see for example, discussion about the hearing mechanism (Harris, 1968)).…”