n.向日性；屈日性
Sunflowers always turn with the sun because of their heliotropism. 向日葵的向光性使它总是随着太阳的方向而移动。
Heliotropism A form of phototropism in which flowers move to point toward the sun, tracking it as it moves across the sky. 向日性：趋光性的一种类型，植物的花在一天内朝向太阳，并随着日光照射的方向而转移方位。
Recent explanations for heliotropism of sunflower 葵花向阳原因新解析
negative heliotropism 背日性,负向日性
Flower heliotropism 花向日性
