%phototropism%

n. [ Photo- + Gr. &unr_; to turn. ] 1. (Plant Physiol.) The tendency of growing plant organs to move or curve under the influence of light. In ordinary use the term is practically synonymous with heliotropism. [ Webster 1913 Suppl. ]

2. (Microbiology) exhibiting movement in a direction toward (positive phototropism) or away from (negative phototropism) a source of light. [ PJC ]