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