. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Geotropic responses in roots present experiments, the 2-watt motor of the kUnostat used in earlier work was exchanged for an 18-watt motor. The khnostat was further equipped with an automatic recording 24-mm camera (Robot) and a counterweight. The camera was rotated together with the plants and by means of micro-switches, the camera would make an exposure every 32 minutes or every 64 minutes. In addition, manua
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Geotropic responses in roots present experiments, the 2-watt motor of the kUnostat used in earlier work was exchanged for an 18-watt motor. The khnostat was further equipped with an automatic recording 24-mm camera (Robot) and a counterweight. The camera was rotated together with the plants and by means of micro-switches, the camera would make an exposure every 32 minutes or every 64 minutes. In addition, manual exposures could be made at any time during the rotation. Measurement of the geotropic responses—One of the purposes of the present study was to determine the so-called presentation time under various conditions. For mass-acceleration of a certain strength, for instance 1 g, the presentation time is generally defined as the time during which the root must be stimulated in order that a minimum response may sooner or Figure 2. Plant chamber. Artemisia seedlings growing between agar platelets on a glass slide and protected by a plastic later become manifest. A minimum response is often defined as the develop- ment of curvatures in 50 per cent of the stimulated roots. The percentage of curving roots, however, is a very crude measure of the response and rather inconvenient for statistical treatment. If one is particularly interested in the magnitude of the reaction under various conditions, it is necessary to measure the curvature itself, and not the number of reacting roots. Photographic recording {Figures 3, 4, and 5) was used in most of the experiments. White or orange light did not show much effect, if any, on the responses. Individual angles were measured to the nearest degree by means of a suitably equipped horizontal microscope. The effect of continuous, unilateral geotropic stimulation Figure 3 and the upper curve in Figure 6" show the development of curvatur
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