Plant Control and Co-ordination
Higher plants and most other plants remain attached to one place and do not move from place to place like animals. They can only change the direction of their organs by means of curvature.
These movements take place due to the difference in the ratio of growth of different parts. It can be further classified as nutational or nastic movements.
Nastic movements are due to differences in the rate of growth on two opposite sides. The direction of a nastic movement is independent of where the signal comes from. It is only the quality, and not the direction, of the stimulus that triggers a response.