Kinetics of upward bending response of gravistimulated snapdragon shoots.
Results

'Simulated time lapse photography'

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In one experiment, 'simulated time-lapse photography' was used to record the gravitropic response of a snapdragon shoot on film. During a period of almost 54 hours, many pictures were taken, after which a composite time-lapse photograph was created on a computer (pict. 1). To get a better view of the actual angles, the gravitropic curvature was measured with a standard protractor (fig. 8). During the first 6 hours the shoot bent upward to the maximum angle of 140^o. The bending was linear with a rate of 28^o. h^-1. No clear lag phase could be detected, although the bending rate in the first hour was lower, around 15^o. h^-1. The 'overshoot' was compensated by bending in the opposite direction until a vertical orientation was reached (Pict. 1 a). This second phase in the bending process was more gradual and took, in this case, 49 hours. In picture 1c the effect is shown 24 hours after reorientation of the shoot to its original vertical position. The bending zone (2nd B.Z.) has moved along the stem.

The general way of measuring gravitropic curvature during experiments is shown in picture 2. With a protractor lined up along the top part of the shoot angles could be recorded with an accuracy of about 1^o.

Figure 8. The gravitropic response of a snapdragon shoot
during the 'time-lapse' experiment depicted in picture 1.
The slides were projected, after wich the angles could be
measured with a standard protractor.