There are two main types of movements found in plants in response to stimuli: Autonomic or spontaneous movement and Induced or Paratonic movement. In this article, we will discuss latter type in detail.
PARATONIC MOVEMENT: The movement due to external stimuli called induced movement. There are two types of paratonic movements: The first is Tropic Movement and the second is Nastic Movement
1) TROPIC MOVEMENT: The word tropic is derived from Greek word “Tropos” means “turn”. In this condition, the whole part or organ shows growth or curvature movement. Tropic movement is in response of unidirectional stimuli. It is clearly seen in symmetrical parts of the plants, such as root and shoot. On the basis of stimulus nature, it is further divided into following types.
- a) Phototropism: This type of tropic movement causes due to unidirectional effect of light. It is also known as Heliotropism. The movement of plant parts towards the light is called positive phototropic movement and the movement of plant’s parts away from the source of light stimuli is called negative phototropic movement.
- b) Geotropism: It is the movement of growth curvature causes in response to gravitational stimulus. The movement of plant’s parts towards the gravitational force called geotropic movement. The movement of plant’s parts away from the gravitational force called negative geotropic movement.
- c) Chemotropism: It is caused due to chemical stimuli. The movement of plants towards chemicals called positive chemotropic movement and some of the parts grow negatively chemotropic.
- d) Hydrotropism: The movement of plant’s parts in response of water stimulus is called hydrotropism.
- e) Thigmotropism: The movement of plant parts in response to touch stimulus is called thigmotropism. When the parts of a plant touch the solid object, the growth on the opposite side of contact increases and the tendrils coiled around the support.
- NASTIC MOVEMENT: Nastic movements are the type of movement which occurs due to non-directional external stimuli. This type of movement mostly is observed in leaves, flowers, petals etc. According to types of stimuli, there are following different kinds of Nastic movement.
- a) Photonasty: The non-directional movements caused by light stimulus are called photonastic movement. It occurs due to the change in light intensity.
- b) Thermonasty: The nastic movement due to temperature stimulus is called thermonastic movement.
- c) Seismonasty: The nastic movement that results due to the shock is called seismonasty
- d) Haptonasty: These are the nastic movements occur due to stimuli of touch. This movement observed in many insectivores plants.
- e) Nytinasty: These are the nastic movements which result from the response to the external stimuli leading to differential growth. These are also called diurnal sleep movement.