tropism

tro·pism

noun \ˈtrō-ˌpiz-əm\

Definition of TROPISM

: involuntary orientation by an organism or one of its parts that involves turning or curving by movement or by differential growth and is a positive or negative response to a source of stimulation; also : a reflex reaction involving a tropism

—tro·pis·tic \trō-ˈpis-tik\ adjective