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Paratonic Nastic Movements

Nastic movements do not depend on the direction of the stimulus and are diffused.

Depending on the type of stimulus, nastic movements may be of the following types.

i) Photonastic - due to light

ii) Thermonastic - due to temperature

iii) Seismonastic - due to touch or shock

iv) Nyctinastic - due to diurnal changes.

nyctinastic movement in oxalis

Nyctinastic Movement of Variation in Oxalis.Unfolded Leaflets and Folded Leaflets

 

Photonastic movements

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These movements are exhibited by florets and leaves which open in the morning and close at night. When the movement is caused by presence or absence of light it is called photonastic movements. These movements are popularly called as sleep movements. They are caused by changes in the osmotic potential of cells of the pulvinus.

Thermonasty

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Flowers of Crocus and Tulip exhibit thermonasty as they open at high temperature and close at low temperature.

Sesimonasty

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These movements take place in response to touch, mechanical, electrical, thermal or chemical. This movement is beautifully shown by the sensitive plant, Mimosa pudica. They are caused by change in the osmotic potential of cells of the pulvinus due to the movement of K+ ions.

seismonastic movement plant mimosa pudica

The stimuli is transmitted through the plant in waves at the speed of about one centimeter per second. Certain chemicals play a role in transmission.

Nutational Movement

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The growth of the shoot tips takes place in a zig zag manner. This is due to alternate change in growth rates on opposite side of the apex. Such movements are very slow and cannot be easily seen. This movement is known as nutation.

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