Fig. 5. Ultrastuctural images of cytokinesis in a polyspermic zygote of S. lomentaria. These sections are shown from the consecutive serial sections of the same cell. (A) This polyspermic germinate has four nuclei after mitosis, and three nuclei (N) are observed in this section. Cell divisions (arrows) do not proceed simultaneously; cytokinesis proceeds further at the upper position than at the lower one. (B) Magnified image of the nascent membranous cell partition seen at the lower arrow in another section (A). Golgi-derived globular vesicles and flat tubular vesicles can be observed near the membranous cell partition. Note that one edge of the cell partition is connected to the plasma membrane. (C,D) The other cell division plane. Vesicle accumulation and fusion during cytokinesis progress add one chloroplast.