An organelle found in the cytoplasm of the majority of plant cells. Plastids are surrounded by a double membrane and show a wide variety of structure, ranging from minute *proplastids
, less than 1.0 μm in diameter, to pigmented *chromoplasts
, 10 μm long with a complex internal arrangement of lamellae. These give colour to plant tissues. Plastids are generally interconvertible, one type being derived from another and capable of differentiating into at least one other form. Many plastids, e.g. amyloplasts and *elaioplasts
, are storage organelles. *Chloroplasts
, the most important plastids, contain chlorophylls, carotenoids, electron transfer compounds, and enzymes, providing a highly organized and efficient photosynthetic organelle.