us for a 1 mm diameter cell, the vacuole can have a diameter of 0.8 mm, leaving only a path width of about 0.1 mm around the vacuole for cytoplasm to flow. The cytoplasm flows at a rate of 100 microns/sec, the fastest of all known cytoplasmic streaming phenomena. Characteristics The flow of the cytoplasm in the cell of Chara corallina is belied by the "barber pole" movement of the chloroplasts. Two sections of chloroplast flow are observed with the aid of a microscope. These sections are arranged helically along the longitudinal axis of the cell. In one section, the chloroplasts move upward along one band of the helix, while in the other, the chloroplasts move downwardly. The area between these sections are known as indifferent zones. Chloroplasts are never seen to cross these zones, and as a result it was thought that cytoplasmic and vacuolar fluid flow are similarly restricted, but this is not true.[citation needed] First, Kamiya and Kuroda, experimentally determined that cytoplasmic flow rate varies radially within the cell, a phenomenon not clearly depicted by the chloroplast movement. Second, Raymond Goldstein and others developed a mathematical fluid model for the cytoplasmic flow which not only predicts the behavior noted by Kamiya and Kuroda, but predicts the trajectories of cytoplasmic flow through indifferent zones. The Goldstein model ignores the vacuolar membrane, and simply assumes that shear forces are directly translated to the vacuolar fluid from the cytoplasm.[citation needed] The Goldstein model predicts there is net flow toward one of the indifferent zones from the other. This actually is suggested by the flow of the chloroplasts. At one indifferent zone, the section with the chloroplasts moving at a downw