Source : Webster's Revised Unabridged Dictionary (1913)

Nyctitropic \Nyc`ti*trop"ic\, a. [From Gr. ?, ?, night + ?
   turning.] (Bot.)
   Turning or bending at night into special positions.

   Note: Nyctitropic movements of plants usually consist in a
         folding or drooping of the leaves, the advantage being
         in lessening the radiation of heat.