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.
a tropism (as of plant roots) in which gravity is the orienting factor
a tropism (as in plant roots) in which water or water vapor is the orienting factor
a tropism in which light is the orienting stimulus
a tropism in which contact especially with a solid or a rigid surface is the orienting factor