Young Brunette Girl Travelling Around The World With Sunflowers

Heliotropism
Sun flowers have a type phototropic response called heliotropism (sun turning); the leaves and flower heads young sunflowers follow the sun and their orientation therefore changes from east to west during the day. The movements become a circadian response and when plants are rotated 180 degrees, the old response pattern is still followed for a few days, with leaf orientation changing from west to east instead. The leaf and flower bud phototropism occurs while the leaf petioles and stems are still actively growing and once mature the movements stop. The movement occurs as the petioles bend or twist during the day and at night they unbend or untwist.