heliotropism

helio- +‎ -tropism

heliotropism (countable and uncountable, plural heliotropisms)

1. The property of some plants of turning under the influence of light; either positively (towards the light) or negatively (away from the light)
   • 1880 November 6, Charles Darwin, Francis Darwin, chapter XII, in The Power of Movement in Plants‎, page 555:

     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; […]

   • 2012, Staff (University of Wisconsin-Madison), Sunflowers inspire more efficient solar power system, R&D Magazine, online:

     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.

• heliotropic

• heliotrope

Borrowed from French héliotropisme.

heliotropism n (uncountable)

1. heliotropism