Thigmotropism
The turning or bending response of an organism upon direct contact with a solid surface or object. Also called stereotropism

Gravitropism
Directional growth of a plant organ in response to a gravitational field roots grow downwards, shoots grow upwards. Achieved by differential growth on the sides of the root or shoot. A gravitation field is thought to be sensed by sedimentation of statoliths (starch grains) in root caps.

Phototropism
Growth or movement of a sessile organism toward or away from a source of light.

Tropism