Modification of the direction of growth, caused by some external influence, such as light; -- sometimes used for motion of an organism toward or away from an external stimulus, more properly called taxis.

Gr. tropos: to turn] • In plants, growth toward or away from a stimulus such as light (phototropism) or gravity (gravitropism).

the movement and response of plants as a result of light, gravity, water, or other causes

Long-term growth of a plant toward or away from a stimulus.