(tropic movement) A directional growth movement of a plant or plant part that occurs in response to an external stimulus from a specific direction. Thus there are positive and negative tropisms depending on whether movement is towards or away from the source of stimulation. The movement or bending is accomplished by unequal rates of growth on the two sides of the organ, usually in response to increased auxin levels in the tissues. Compare nastic movements , taxis. See phototropism , geotropism , chemotropism ; orthotropism , plagiotropism , diatropism. |
