WATER RELATIONS IN THE CELL: I. THE CHLOROPLASTS OF NITELLA AND OF SPIROGYRA
The Journal of General Physiology
Of fundamental importance in the metabolism of the cell is the behavior of water. Of especial interest is the giving up of water by one part of the cell to another as anidn ication of changes in metabolism or constitution. An example of this is seen in the changes in volume of the nucleus which may occur under normal conditions in certain cells. Such transfers can be produced in Nitella experimentally. When cells t are exposed to 0.5 M NaC1 the salt may penetrate the outer protoplasmic surface
... otoplasmic surface more rapidly than the inner so that water is withdrawn from the sap and the protoplasm increases in volume at the expense of the vacuole. Another example is seen in the decrease in volume often observed in the chloroplasts of Nitella 2 under natural conditions. This may also be produced experimentally. The normal condition of the chloroplasts is shown in Fig. 1 . They are imbedded in the aqueous layer W of the protoplasm lying between the outer, nonaqueous surface layer of the protoplasm X, and the corresponding inner layer, y.s The outer portion of the layer W consists of a stiff gel containing the chloroplasts. The inner portion of W is liquid and is usually in active motion. 4 When sufficient centrifugal force is applied the long rows of chloroplasts may separate and each row then acts as if it were a stiff gel forming a long straight rod of protoplasm containing a single series of chloroplasts. When cells, carefully removed from their natural surroundings, are brought into the laboratory and examined it is often possible to find areas where the chloroplasts have contracted to form spherical (or nearly spherical) bodies (Fig. 1) . Since the diameter of the sphere is not greater than the smaller diameter of the ellipsoid body of the chloroplast before contracting it is evident that there must be a loss of volume and a consequent transfer of water to other parts of the cell. To what extent this must be attributed to injurious or pathot Osterhout, W.