n. The property of some plants of turning under the influence of light; either positively (towards the light) or negatively (away from the light)
the GNU version of the Collaborative International Dictionary of English
n. The phenomenon of turning toward the light, seen in many leaves and flowers.
The Century Dictionary and Cyclopedia
n. In botany, the tendency of growing organs to bend toward or in some cases away from the light, due in the former case to the retarding influence exerted by the light upon their growth on the side of the highest illumination.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. an orienting response to the sun
Word Usage
"Besides the algae in their skin, they had altered hormone levels with predispositions toward heliotropism and nudity, plus numerous other "improvements.""