The phenomenon which is influenced by auxin and also played a major role in its discovery :

Auxin influences phototropism, i.e., the growth of the plant in response to light stimulus and this phenomenon played a major role in its discovery. Charles Darwin and his son Francis Darwin observed that the coleoptile of canary grass responded to the unilateral illumination by growing towards the light source (phototropism). They concluded that the tip of coleoptile was the source of auxin and was the site of transmittable influence that caused the bending of the entire coleoptile.