Movement of plant parts in reponse to the force of gravity is called
Geotropism
Growth or movement of plant parts in response to the force of gravity is called geotropism. The downward growth of roots is an example of positive geotropism. Shoots grow upward showing negative geotropism.
Chemotropism - the movement or growth in plants in response to chemicals.
Phototropism - the movement or growth in plants in response to light.
Hydrotropism - the movement or growth in plants in response to water.