Paratonic movement in plants and kinds of paratonic movement

PARATONIC MOVEMENTS

The plant movement due to external causes are called paratonic movements. These are following types.

• Tropic Movement (Directional + Respond to External Stimuli)
• Nastic Movement (Non-directional + Respond to External stimuli)

(1) Tropic Movement (Directional + Respond to External Stimuli): It is the kind of paratonic movement in which curvature or turning of whole organ occurs due to external stimuli like light, gravity or touch. It is directional movement. Following are common tropic movements:

(i) Photorpism: The tropic movement of the organ of plant in response to light is photorpism roots and stems show phototropism. Actually, differential growth is reason of movement.

(ii) Thigmotropism: The tropic movement in response to stimulus of touch is known as thigmotropism. Climbing vines are coiled by thigmotropic movement. When vines come in contact with sonic solid object, in this situation, the growth on the opposite sides of contact increases and the tendrils coils around the support.

(iii) Chemotropism: The tropic movement in response to stimulus of chemicals is called chemotropism.

The hyphae of fungi respond to certain chemicals.

(iv) Hydrotropism: The tropic movement of plant parts in response to stimulus of water is termed as hydrotropism.

The growth of roots toward water due to ❝positive hydrotropism❞.

The growth of shoots away from the water is ❝negative hydrotropism❞ or negative hydrotropic.

(v) Geotropism: The tropic movement of plant parts in response to gravity is called geotropism.

Roots show positive geotropism and shoots display negative geotropism.

(2) Nastic Movement: (Non-directional + Respond to External stimuli)  The non-directional movement of plant parts in response to external stimuli are called nastic movement.

(i) Nyctinasty: The nastic movement in response to external stimuli in which differential growth take place is known as Nyctinastic movement or nyctinasty.

These are due to turgor and growth changes. It has two types.

(a) Photonasty: Opening and closing of flowers due to photonasty. The nyctinastic movement in response to light is called photonasty.

(b) Thermonasty: In this case the growth is respond to temperature.

For example the flower of Tulip close at night due to rapid growth in lower sides in the petals. Thus petals move upward and inward.

(ii) Haptonastic Movement: The non-directional movement of plant parts in response to contact is called haponasty or haponastic movement.

Venus fly trap has haponastic condition.