The cell-membrane may become modified by the process of lignification, suberization, cuticularization or gelatinization.
As in other cell-walls, so here the older membranes may be altered by deposits of various substances, such as resin, calcium oxalate, colouring matters; or more profoundly altered throughout, or in definite layers, by lignification, suberization (Trametes, Daedalea), or swelling to a gelatinous mucilage (Tremella, Gymnosporangium), while cutinization of the outer layers is common.
The leaf scar is protected by a corky change (suberization) in the walls of the exposed cells.