che·mo·tax·is 
(kē′mō-tăksĭs, kĕm′ō-)
(kē′mō-tăksĭs, kĕm′ō-)n.
The characteristic movement or orientation of an organism or cell along a chemical concentration gradient either toward or away from the chemical stimulus.
che′mo·tactic (-tăktĭk) adj.
che′mo·tacti·cal·ly adv.