An organelle within a plant cell, often occurring in large numbers. Apart from the nucleus, plastids are the largest solid inclusions in a plant cell. For convenience they are classified into those containing pigments (chromoplasts) and those that are colourless (leucoplasts), although changes from one to the other frequently occur. Plastids develop from proplastids, colourless bodies found in meristematic and immature cells; they also arise by division of existing plastids. See also chloroplast.
Subjects: Biological Sciences.