The plastid (Greek: πλαστός; plastós: formed, molded – plural plastids) is a major double-membrane organelle found in the cells of plants, algae, and some other eukaryotic organisms. Plastids were discovered and named by Ernst Haeckel, but A. F. W. Schimper was the first to grant them a clear definition. Plastids are the site of manufacture and storage of important chemical compounds used by the cell.