Nuclei appear bright white while cell boundaries are dark in these confocal images of fixed, dissected Arabidopsis ovules stained with propidium iodide (PI) and imaged by confocal microscopy. The dotted white line outlines the gametophyte, which can be recognized by its large, smooth-staining cells and the presence of large nuclei. The number and position of the nuclei allow the determination of the developmental stage, as shown below. I took these images in the Bednarek lab in the Biochemistry department at the University of Wisconsin, Madison during my PhD studies; they were published in a study of the Arabidposis dynamin related protein 2 (DRP2) mutants (Backues et al. 2010 Plant Cell 22:3218-31) Another way to image ovules and the developing gametophyte is by embedding and sectioning the ovules and staining the sections with toluidine blue; here are images of Arabidopsis ovules imaged this way.