Tropisms are movements or changes in posture that a living being normally makes in response to a continuous environmental stimulus. Plants have hormones that respond to the gravitational impulse of our planet. Gravity deeply influences their growth and development (positive geotropism) and plants have been found to bend in response to gravity due to redistribution of the plant hormone auxin at the root tip, so that auxin is redistributed to the underside of a root that grows when it is rotated 90 degrees, the stems will still grow upward, away from the center of the Earth (negative geotropism), just as roots will always grow in the reverse direction (positive geotropism).
