chloroplast
    n 1: plastid containing chlorophyll and other pigments; in
         plants that carry out photosynthesis

Chloroplast \Chlo"ro*plast\, n. [Pref. chloro- + Gr. ? to mold,
   form.] (Biol.)
   A plastid containing chlorophyll, developed only in cells
   exposed to the light. Chloroplasts are minute flattened
   granules, usually occurring in great numbers in the cytoplasm
   near the cell wall, and consist of a colorless ground
   substance saturated with chlorophyll pigments. Under light of
   varying intensity they exhibit phototactic movements. In
   animals chloroplasts occur only in certain low forms.
   [Webster 1913 Suppl.]