Phototonus \Pho*tot"o*nus\, n. [NL. See {Photo-}, and {Tone}.]
1. (Bot.) A motile condition in plants resulting from
exposure to light. -- {Pho`to*ton"ic}, a.
[1913 Webster]
2. (Physiol.) An irritable condition of protoplasm, resulting
in movement, due to a certain intensity of light. --
{Pho`to*ton"ic}, a.
[Webster 1913 Suppl.]