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Definition of: phototonus
(fō·tot′ə·nəs) noun Biol.
1. The influence of light upon the movement and the growth of plants.
2. The condition thus induced.
3. Increased irritability or motility induced by exposure to light. [<NL <Gk. phōs, phōtos a light + tonos tension. See TONE.]
—pho·to·ton·ic (fō′tə·ton′ik) adjective
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