Thigmotropism is a movement in which a plant moves or grows in response to touch or contact stimuli. The prefix thigmo- comes from the Greek for "touch" (θιγμός). Usually thigmotropism occurs when plants grow around a surface, such as a wall, pot, or trellis. Climbing plants, such as vines, develop tendrils that coil around supporting objects. Touched cells produce auxin and transport it to untouched cells. Some untouched cells will then elongate faster so cell growth bends around the object. Some seedlings also exhibit triple response, caused by pulses ofethylene which cause the stem to thicken (grow slower and stronger) and curve to start growing horizontally.