Representative cross-section with collapsed cell rows (indicated by white arrows) in the LW of stressed oaks. Differentiation in EW, LW and newly formed LW after severe drought stress (collapsed cells) is indicated on the lefthand scale. Red and blue coloured cell walls indicate dead (lignified) and living (non-lignified) cells, respectively. The white bar represents 1 mm. (A color version of this figure is available at www.afs-journal.org.)