\Pho`to*tax"is\, Phototaxy \Pho"to*tax`y\, n. [NL.
phototaxis; photo- + Gr. ? an arranging.] (Biol.)
The influence of light on the movements of low organisms, as
various infusorians, the zo["o]spores of certain alg[ae],
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.