Where the specific stimulus is light, the phenomenon is phototropism ( "light-turning" G).    From Wordnik.com.  [The Human Brain]

Make sure you look at the movies for morning glories twining, and corn seedling phototropism.    From Wordnik.com.  [Rambles at starchamber.com » Blog Archive » Green machines] Reference

Maybe there's some phototropism in there as well they seem to be moving to the shadow at the top?.    From Wordnik.com.  [Clustering of the intertidal snail Batillaria minima] Reference

It's not a phototropism, but a "sun" tropism following the position of the sun.    From Wordnik.com.  [Israelated - English Israel blogs] Reference

Since then, the study of phototropism has been a cornerstone of plant science research.    From Wordnik.com.  [News from The Scientist] Reference

They took photos to document phototropism in plants - how plants grow in the direction of the sun - and erosion.    From Wordnik.com. Reference

Almost 200 years ago, researchers first began to characterize plant responses to sunlight-among them, the propensity of a plant's tip to grow towards the light and its root to grow away from the light, a phenomenon called phototropism.    From Wordnik.com.  [News from The Scientist] Reference

Function: action specially fitted for a thing (e.g., locomotion, phagocytosis, phototropism, functioning as a molecular motor, energy transduction, etc.); behavior: the activity detected by the observer (e.g., deception, flight, chemotaxis, etc.).    From Wordnik.com.  [Citizendium, the Citizens' Compendium - Recent changes [en]] Reference

Function: activity specially fitted for a thing (e.g., locomotion, phagocytosis, phototropism, functioning as a molecular motor, energy transduction, etc.); behavior: the activity detected by the observer (e.g., deception, flight, chemotaxis, etc.).    From Wordnik.com.  [Citizendium, the Citizens' Compendium - Recent changes [en]] Reference