Figure 6 Cell walls, planes of cell division, and form of the plant body illustrated through embryogenesis in a higher plant. Embryo formation in Arabidopsis provides an example of highly regulated planes of cell division during formation of a specifically shaped plant body. Arrowheads in A to C show successive planes of division in very young pro-embyos. Subsequent divisions (D-H) build up a heart-shaped embryo with surface and inner walls and embryonic root and cotyledons. D, The complete suspensor filament as well as the globular pro-embryo. In A to E the embryos are embedded in endosperm tissue in the embryo sac; in F to H they have been isolated from their embryo sacs. (Based on Gunning and Steer 1996)