Tropism is known as the directional movement which occurs in response to an external stimulus. Even though plants cannot move, they are still able to change their direction of growth to a desired condition. The particular type of tropism shown in this picture is thigmotropism. Thigmotropism is the growth of a plant in response to contact or touch. This picture shows that this plant grew inward to not collide with the fence and possibly stunt its growth.