pho·to·pe·ri·od·ism 
(fō′tō-pîrē-ə-dĭz′əm)
(fō′tō-pîrē-ə-dĭz′əm)n.
An organism's response or ability to respond to changes in photoperiod.
- radio collar
- radio compass
- radioecological
- radioecologist
- radioecology
- radio frequency
- radio frequency identification
- radio galaxy
- radiogenic
- radiogram
- radiograph
- radiographer
- radiographic
- radiographically
- radiography
- radioimmunoassay
- radioimmunological
- radioimmunology
- radioiodine
- radioisotope
- radiolabel
- radiolarian
- radiolocation
- radiologic
- allocation