tropism

ckslick 1/31/13 p3

tropism

The turning or bending movement of an organism or a part toward or away from an external stimulus, such as light, heat, or gravity

geotroism

The growth of a living organism in response to gravity, as the downward growth of plant roots.

hydrotropism

Growth or movement in a sessile organism toward or away from water, as of the roots of a plant

phototropism

Growth or movement of a sessile organism toward or away from a source of light.