Source : Webster's Revised Unabridged Dictionary (1913)

Chemotaxis \Chem`o*tax"is\, n. Formerly also Chemiotaxis
\Chem`i*o*tax"is\ [Chemical + Gr. ? arrangement, fr. ? to
   arrange.] (Biol.)
   The sensitiveness exhibited by small free-swimming organisms,
   as bacteria, zo["o]spores of alg[ae], etc., to chemical
   substances held in solution. They may be attracted ({positive
   chemotaxis}) or repelled ({negative chemotaxis}). --
   {Chem`o*tac"tic}, a. -- {Chem`o*tac"tic*al*ly}, adv.

Source : WordNet®

chemotaxis
     n : movement by a cell or organism in reaction to a chemical
         stimulus