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. Chloroplast: 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 form proplastids by a fission like process..