Nastic Responses
Are non-directional movements of parts of plants in response to diffuse stimuli i.e. stimuli that does not come from a particular direction but rather comes from all over.
The various types of nastisms are named according to the stimulus involved. These include;
- Nyctinasty (temperature and light)
- Haptonasty (contact)
- Chemonasty (chemicals)
- Hydronasty (water)
- Nyctinasty (Sleep movement)
Non-directional response to differences in light intensity and temperature changes of the day and night e.g. sunflower.
If the response is specifically for light then it is called photonasty, open in presence of light and close in its absence and if it is specifically for temperature changes then it is called thermonasty as in flowers of some plants that open with increase in temperature and close with decrease in temperature.
- Haptonasty
Non-directional response to contact (touch).
Example; the closing of leaves of Mimosa pudica when touched. And, also when a Venus flytrap plant traps insects to obtain nitrogen from them.
- Chemonasty
Non-directional response to chemical substances.
Examples;
- Hydronasty
Non-directional response to changes in humidity.
Example; when certain flowers fold their petals when the air is moist.
Survival Value of Nastism
- Protection of the inner delicate parts of the flowers.
- Reduction of transpiration.
- Regulation of temperature.
- A way of obtaining some limited mineral nutrients.