Darwin and his son observed that the coleoptiles of canary grass responded to unilateral illumination by growing towards the light source. This is called phototropism. They performed series of experiments which concluded that the tip of coleoptile was the site of transmittable influence that caused the bending of the entire coleoptile. F.W. Went isolated auxin from the tips of coleoptiles of oat seedlings and concluded that phototropism of oat seedlings occur. They also concluded that phototropism in the tips of coleoptiles is due to the polar movement of auxin in the stem. So, the correct answer is 'it demonstrated polar movements of auxins'.