The parameters affected by salinity in salt-sensitive plants are reviewed. Turgor is the potential energy which powers extension growth, but is not a parameter which controls the growth process. Cell expansion is affected by phytohormones, and salinity modifies the phytohormonal balance of the plant; one of the major effects of salinity on growth results from a modification of the phytohormonal balance. Exposure to salt of certain plant genotypes, under appropriate conditions, results in an increase in salt resistance, which has been termed adaptation. The capacity to adapt is limited to a precise period of development. The process of adaptation is accelerated by abscisic acid and inhibited by cytokinin. It is a genetic character which is not a property of all genotypes. Adaptation is transmitted to the next generation, which suggests that it involves a modification of the genome. In plants, genome organization and expression are modified during development and under various types of environmental conditions. These changes in DNA are generally transitory, but under defined conditions they can be permanent and hence heritable. Changes in salt tolerance have been reported in the literature in the past but not recognized as adaptation because the authors were not aware of the phenomenon.