Plastids are small bodies found free in most plant cells. These are found absent in fungi, certain bacteria, algae and multicellular animals. The plastids can be categorized to :
Chromoplasts : Coloured (other than green) plastids.
Chloroplasts : Green coloured plastids :
Leucoplasts : Colourless plastids.
All these three are double membrane bound structures which are mainly used for trapping radiation and storage purposes.
New plastids arise from proplastids by a fission like process.