The preservation of the developmental biology film series was made possible by generous contributions from distinguished university professor of geosciences Lynn Margulis, Terence Malik, Chelsea Green Publishing, the politics and practice of sustainable living, the Hardy Lane Foundation, the International Symbiosis Society, Geobook Studio, publisher of The Biggest Picture, Hummingbird Films, producer of the documentary, Symbiotic Earth, and supporters of the Lynn Margulis Archive at Scholar Works. The tropical marine alga calurpa is rather like a small fern. It grows naturally on the seabed and it may extend for several meters. Unlikely though it may seem, the calurpa plant consists of but a single cell, which contains a great many nuclei. Calurpa shows clearly that a single cell of very large size can possess structural and functional differences similar to those which are to be found in multicellular plants. From an apparent stem or rhizome, growing horizontally, root-like structures grow down, while green leaf-like projections or fronds grow up. Since the cytoplasm is continuous throughout the plant, organelles are free to move from one region to another. The gross movement of chloroplasts for instance, is seen here in time-lapse as a dark green shadow moving to the left from the tip of the rhizome. Both of the rhizome is restricted to elongation at its tip. This process typifies the mode of root growth of multicellular land plants and is also similar to the growth of pollen tubes. The root-like structures are delicate extensions of the wall of the rhizome. They are analogous to the root hairs of the higher plants. In most land plants, the development of leaves from an apical meristem is obscured from view by bud scales and older leaves. But in calurpa, the formation of the intricate leaf-like fronds takes place in full view. The tiny protrusion on the upper surface of the rhizome extends to form an erect stalk. From the very tip of this stalk, pairs of flaps resembling leaflets arise in regular synchrony, growing in a single plane. The growth you see here took four days. But remember, you are not looking at a multicellular structure like a fern-fron or a pinnete leaf. You are watching a single cell, parts of which are being elaborated into three different shapes. The rhizome, the rootlets and the leaf-like fronds. Perhaps the principles explaining the development of shape in multi-nucleate algae and in the higher plants as well may be explored more readily in this organism where the phenomena are displayed in such a dramatic and accessible way.