SOME GROSS CORRELATIONS BETWEEN GROWTH ENLARGEMENT AND THE SOLUTE AND WATER RELATIONS OF PLANTS, WITH SPECIAL EMPHASIS ON THE RELATION OF TURGOR PRESSURE TO DISTENTION OF CELLS

In discussions of the dynamics of the growth process, three main views regarding the mechanism of cell enlargement are held. One suggests "that the cell wall must first be subjected to elastic (reversible) or plastic (irreversible) stretching as a result of a turgor pressure developed by the cell sap" (16). It is assumed that this is then followed by addition of material substance to the wall through intussusception or apposition, or if unaccompanied by the incorporation of new material, by attenuation of the wall accompanying increase in area. A second idea suggests "that active growth of the cell wall," as a result of "the intercalation of additional molecules between those already present, . . . is the primary step in cell enlargement. Entrance of water into the cell is considered to be a result of the increase in the volume of the cell rather than its cause" (16). A third concept, related in part to each of the former, suggests that the initial step is an increased plasticity of the cell wall, followed by a lowering of the turgor pressure and influx of water, tending to approach a new osmotic equilibrium (compare (12)). These views, and experimental results in support of each, are presented at length in a recent monograph (7). Certain limited experimental data, published earlier (15) for other purposes, would appear to afford evidence greatly favoring the first hypothesis. It is desired to represent these data, with further information, and attempt to show that, under the conditions studied, the distention of roots is primarily the result of turgor pressure developed in the internal phases of cells.