. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RHYTHMS IN ACETABULARIA. I 665 CO to o I CL or < cc m cc I 2 O to Ul. NOON MN V NOON MN FIGURE 5. The effect of a single 8-hour light period on the phase of the rhythm of oxygen production. Prior to the start of the experiment the cells had been in continuous light for 1 week, during which the time of maximum output had shifted to 1 to 2 o'clock in accordance with a free-running period somewhat in excess of 25 hours. The amplitude of the circadian oscillation diminishes rapidly under high- intensity illumination, but the
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. RHYTHMS IN ACETABULARIA. I 665 CO to o I CL or < cc m cc I 2 O to Ul. NOON MN V NOON MN FIGURE 5. The effect of a single 8-hour light period on the phase of the rhythm of oxygen production. Prior to the start of the experiment the cells had been in continuous light for 1 week, during which the time of maximum output had shifted to 1 to 2 o'clock in accordance with a free-running period somewhat in excess of 25 hours. The amplitude of the circadian oscillation diminishes rapidly under high- intensity illumination, but the vestige of the rhythm that remains after 3 or 4 days indicates that its period is unaffected. The free-running rhythm is exhibited with maximum amplitude at intermediate light intensities. In none of these experi- ments was there any indication that either the period or the phase of the free- running rhythm was affected by light intensity. In order to establish that the photosynthetic apparatus was not adapting to whatever light intensity was being used to demonstrate the free-running rhythm, experiments were programmed to give indications both to the capacity and activity of photosynthesis throughout the cycle (Fig. 4). This was accomplished by giving 15-minute exposures to high intensity (1000 ) illumination every 2 hours on a continuous background of moderate intensity (250 ). The maximum rates recorded at the lower intensity did not exceed the minima in the high intensity cycle. This result clearly shows that the maximum photosynthetic capacity of Acetabiilaria remains well above the range of the oscillations in activity observed at low or intermediate intensities. It is evident that capacity and activity vary simultaneously, and that the former undergoes changes of greater amplitude. Resetting the rhythm of photosynthesis Figure 5 illustrate an experiment performed with cells that had previously been held in continuous illumination of 300 for one week af
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
