. Practical text-book of plant physiology. Plant physiology. ALTERNATING AND INTERMITTENT STIMULATION 79 acquires the power of curvature, then set up a reaction to direct the tip 119. Alternating and Intermittent Stimulation. It is found that an intensity or duration of the geotropic stimulus not suffi- cient to call out a reaction alone, may do so, if repeated at regu- lar intervals for a sufficient number of times. One method of accomplishing this demonstration consists in placing the stem of a grass in a moist chamber and revolving it on its axis in a hori- zontal position. The
. Practical text-book of plant physiology. Plant physiology. ALTERNATING AND INTERMITTENT STIMULATION 79 acquires the power of curvature, then set up a reaction to direct the tip 119. Alternating and Intermittent Stimulation. It is found that an intensity or duration of the geotropic stimulus not suffi- cient to call out a reaction alone, may do so, if repeated at regu- lar intervals for a sufficient number of times. One method of accomplishing this demonstration consists in placing the stem of a grass in a moist chamber and revolving it on its axis in a hori- zontal position. The clinostat is so arranged however that the stem remains motionless for a regular length of time and is then revolved an equal period, then is held motionless, etc. After a. Fig. 35. Showing method of cutting off shoots under water. time curvature is produced as a result of the summation of the effects. Most interesting results have been obtained by F. Darwin and D. Pertz by giving a stem two sets of diametrically opposed stimuli. The clinostat was arranged to make half revolutions with periods of rest so that the stem bent first in one direction then in another. As the result of this alternating stimulation the stem acquired a regular rhythm of movement which continued 1 Czapek, F. Ueber den Nachweis der geotropischen Sensibili tat der Wurzelspitze. Jahrb. Wiss. Bot. 35 : 313. 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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