The movement of part of a plant in response to external stimulus of no particular direction is
taxism
tropism
haptotropic movement
nastic movement
Correct answer is D
Taxism: oriented movement of a motile organism in response to an external stimulus, as toward or away from light.
A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus.
In tropisms, this response is dependent on the direction of the stimulus.
The movement or directional growth of plants or plant organs (as the tendrils of climbing plants) in response to the stimulus of touch.
The non-directional movement (of plants) in response to a stimulus (e.g. humidity, temperature, light irradiance, nutrients, gravity, etc.