heliotropism

noun

1. (countable, uncountable)The property of some plants of turning under the influence of light; either positively (towards the light) or negatively (away from the light).

   “As soon as the faintest ray of light reaches a seedling, heliotropism will guide it through any crack in the soil, or through an entangled mass of overlying vegetation; […]”

   “A field of young sunflowers will slowly rotate from east to west during the course of a sunny day, each leaf seeking out as much sunlight as possible as the sun moves across the sky through an adaptation called heliotropism.”