Most plants, and some fungi, microorganisms, and lower forms of animal life, respond to stimuli that act with greater intensity from one direction than another by orienting themselves with respect to the direction in which the stimuli are acting. These...

A tropism (from Greek, tropos, to turn) 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...