tropism

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tropism (tropic movement) A directional response by a plant to a stimulus. It may be positive or negative (i.e. towards or away from the source of the stimulus). The plant may respond by growth or turgor changes so that parts of it bend towards, away from, or at right angles to the direction of the stimulus. The suffix-tropism is used in relation to responses to particular stimuli; e.g., phototropism is a response to light, geotropism to gravity, and chemotropism to a chemical substance.

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