. Practical text-book of plant physiology. Plant physiology. 74 RELATION OF PLANTS TO GRAVITATION horizontal position for 60 to 80 minutes. If placed in this posi- tion for a less time, then revolved on a clinostat the relation of the length of the reaction time to the duration of the stimulus (exposition time) may be found. The rotation of an organ on its own axis, in a position in which it receives geotropic stimulation presents all sides of the sensory zone to the action of the stimulus, and thus brings the organ into a state of tetanus so well balanced that no curvature is shown. If gravit
. Practical text-book of plant physiology. Plant physiology. 74 RELATION OF PLANTS TO GRAVITATION horizontal position for 60 to 80 minutes. If placed in this posi- tion for a less time, then revolved on a clinostat the relation of the length of the reaction time to the duration of the stimulus (exposition time) may be found. The rotation of an organ on its own axis, in a position in which it receives geotropic stimulation presents all sides of the sensory zone to the action of the stimulus, and thus brings the organ into a state of tetanus so well balanced that no curvature is shown. If gravity is replaced by centrifugal force, or rather, 4b 3h 2h Us 1234 6 8 10 15 20 25 30 35 40 Fig. 32. Curve showing relation of amount of centrifugal force and reaction time of roots of Lupinus albus. Reaction times are denoted by the figures along the verti- cal line, and amount of centrifugal force in terms of gravity along the horizontal line. After Czapek. counteracted by it by being given in a different plane, an amount of the centrifugal force amounting to but a thousandth of gravity may be followed hy* a reaction after a period of six hours, and when the centrifugal force is increased to 40 g. the reaction time is shortened to 45 minutes. The angle of divergence from the normal geotonic position of the organ exerts such effect that the maximum stimulus is re-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original MacDougal, Daniel Trembly, 1865-1958. New York [etc. ] Longmans, Green, and Co.
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