A potted plant having straight parts A and B was placed horizontally on its side as shown in Figure (i). After a few days it was observed that the parts A and B of the plant acquire new positions as shown:

(a) Name the phenomenon exhibited by the position of plant parts A and B in Figure (ii)

(b) Name the stimulus (other than sunlight) which causes plant part A to grow and bend upwards, and plant part B to bend downwards.