Source : Webster's Revised Unabridged Dictionary (1913)

Phototonus \Pho*tot"o*nus\, n. (Physiol.)
   An irritable condition of protoplasm, resulting in movement,
   due to a certain intensity of light. -- {Pho`to*ton"ic}, a.

Phototonus \Pho*tot"o*nus\, n. [NL. See {Photo-}, and {Tone}.]
   (Bot.)
   A motile condition in plants resulting from exposure to
   light. -- {Pho`to*ton"ic}, a.