The movement of solutes into plants can and should be expressed in terms of the specific free energies of the solute molecules. Similar expressions have been developed for the flow of water. The mathematical relation between the specific free energies of the solute and the water in solutions and in the osmometer systems of the plant has been presented. The terminology is consistent with thermodynamic and physico-chemical principles. The movement of solutes into plants can be accomplished through several modes of action. These possible modes of flow include simple diffusion, Donnan equilibria, pressure effects, adsorption including exchange adsorption, and metabolic accumulation. The metabolic accumulation of solute is probably a universal mode of net influx. The accumulation is directly related to oxidative catabolism for its source of energy. This energy is applied to the solute molecules through some type of solute-cytoplasmic interaction increasing their free energy such that the molecules of a solute species tend to move with and against the direction in which their concentration in solution decreases. The mechanism for conversion or transfer of chemical into mechanical energy remains to be elucidated.