If a broad bean seedling is placed in the dark in a horizontal position, its shoot will bend upwards and its root downwards. The root tip is showing a positive geotropism because it is growing towards gravity so that it has more chance of finding moisture. The shoot tip on the other hand is showing a negative geotropism because it is growing away from gravity to have more chance of finding light.
Because the motor turns the disc and germinating seeds around very slowly, any directional stimulus that may be acting on the seeds is eliminated by the movement; every side of the seedling is acted on by gravity, so the roots will grow horizontally.
2) Describe and give examples of why a clinostat is used. What sort of investigations would use one?
A clinostat is a piece of apparatus consisting of an electric motor turning a cork disc which can be set to rotate in a vertical or horizontal plane by a motor. Germinating seeds can be attached to the disc. Clinostats are used for control experiments, and make factors uniform (evenly distributed).
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