Phototropism
Phototropism is one of the many plant tropisms or movements which respond to external stimuli.  Growth towards a light source is a positive phototropism, while growth away from light is called negative phototropism. Most plant shoots have positive phototropism. Roots usually have negative phototropism, though gravitropism may play a larger role in root behavior and growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them.