Recent Examples on the WebThat thick layer of peptidoglycan helps hold in a purple dye called crystal violet. Beth Mole, Ars Technica, 16 Aug. 2019 By contrast, cells with more complex cell walls consisting of a relatively thin layer of peptidoglycan plus an outer membrane don’t hold in crystal violet as well. Beth Mole, Ars Technica, 16 Aug. 2019