{ ‖, n. [ NL. phototaxis; photo- + Gr. &unr_; an arranging. ] (Biol.) The influence of light on the movements of low organisms, as various infusorians, the zoospores of certain algæ, etc.; also, the tendency to follow definite directions of motion or assume definite positions under such influence. If the migration is toward the source of light, it is termed
positive phototaxis; if away from the light,
negative phototaxis. -- Pho`to*tac"tic a. -- Pho`to*tac"tic*al*ly, adv. [ Webster 1913 Suppl. ]