The Flower of Kalanchoe
The tiny red flowers of Kalanchoe blossfeldiana open and close at 23-hour intervals. They do this for a week even when plucked from the plant and placed in a vial of sugar water under constant green light, at a constant temperature. Though blind to green,
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The Flower of Kalanchoe
The tiny red flowers of Kalanchoe blossfeldiana open and dose at 23-hour intervals. They do this for a week even when plucked from the plant and placed in a vial of sugar water under constant green light, at a constant temperature. Though blind to green, the ftower's dock is sensitive to red light. By exposing the ftower to red light ofintensity several watts per square meter for minutes to hours, one disrupts the normal rhythmicity. In most cases, it recovers sufficiently within four days so that a phase shift can be measured.
A:
Type 0 Resetting
The first systematic experiments ofthis sort were conducted by Zimmer (1962). Her results show wh at I take to be type 0, or "strong", re setting in response to a two-hour light pulse. The original publication draws a type 1 curve through the data (Figure 1) by inserting an 18-hour data-free discontinuity through the phase measurements. This seems to me an exaggerated concession to the theoretical prejudice that, in connection with phase shift plots, what goes up must come down. If the data must be construed as type 1 resetting, then there must be an extremely steep part ofthe curve and one would expect more variance ofthe measured phase shift near this point. As this is not observed, it seems to me that the phase jump probably doesn't exist and that the data fit better in the pattern oftype resetting. Phase shifts can also be measured substantially in advance ofthe petal rhythm's settling down to a steady cyde (wh ich, in fact, it never does in Figure 2). This is because of the fortunate circumstance that, unlike many circadian rhythms such as the eclosion rhythms of Chapter 20, Kalanchoe's petal movement rhythm can be monitored almost continuously. Instead ofhaving to wait for an event to signal passage of phase 0, at every moment we have at least two measurements in hand, namely, flower openness and the rate of change of that measurement. Let's call these position P and velocity V. If the mechanism of petal movement involves no more than two important variables then by measuring any two functions of state we should be able to distinguish the system's state from nearby other states. This should sufllce to distinguish the latent phase (Chapter 6) of the rhythm while still far from an attracting cyde.
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A. T. Winfree, The Geometry of Biological Time © Springer Science+Business Media New York 1980
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Figure 1. An early resetting experiment using Kalanchoe's petal movement rhythm. Alternating maxima and minima of openness are plotted to the right following a light pulse given at the time indicated along the diagonal slash. Prior to the stimulus (left), all flowers were synchronous. After stimulus and transients, these rhythms fall into the type 0 pattern, paralleling the stimulus rather than the controls. Zimmer's dotted curve, however, adheres to the type 1 pattern, progressively distorting a parallel to the controls (the prestimulus pat
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