Movement is a characteristic of living beings. Animals show perceptible movement. They always move to fulfil their basic necessities like food, shelter and clothing. However, the movement in plants may or may not be perceptible.
In lower plants particularly among algae like Chlamydomonas movement is very pronounced. But the higher plants such as perennial trees remain fixed to the soil. But, their organs like branches, leaves or flowers show movement. Sometimes, movements take place spontaneously without the effect of external stimuli.
This is called spontaneous or autonomic movement. But in most cases, the movement occurs in response to external stimuli which may be called as induced or paratonic movement.
All parts of the plants are sensitive to stimuli. Specialized regions called receptive regions receive the stimulus and transmit it to the regions where responsive movements are affected. These are called responsive regions.
A stimulus may not produce a response immediately. It has to act for sometime before the plant organ may respond. This period, necessary for a stimulus to induce a response is called presentation time. The time taken by a plant organ to manifest its response to a stimulus is called reaction time.