Source : Webster's Revised Unabridged Dictionary (1913)

Phototaxis \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.