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.