phototaxy
Pho`to*tax"is, Pho"to*tax`y, n. [NL. phototaxis; photo- + Gr. an arranging.] (Biol.) Defn: The influence of light on the movements of low organisms, as various infusorians, the zoöspores 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.