Tropism
MOVEMENT OF AN ORGANISM, OR PART OF AN ORGANISM, IN RESPONSE TO AN EXTERNAL SOURCE OF STIMULUS, USUALLY TOWARD OR AWAY FROM IT.
TROPISM
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 (as opposed to nastic movements which are non-directional responses).