A 4 day cress seedling showing a heliotropic response towards an "artifical sun" (the same lamp as used for the phototropism shown with video 1 but which moved in an arc directly over the seedlings during a 12 h period). The shadow pointer seen on the background of the above frame on the right moves to indicate the angle of incidence of the "sun". Note the initial curvature towards the right during "morning", then the reverse curvature in late morning and for the rest of the day when the seedlings track the "sun" quite effiiciently. The frames (320 x 240) were captured every 15 min and the duration of the sequence is nearly 12h.
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File format Windows .avi file. Size 1.30 Mb.