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It is apparent that heightened interest in salinity and related factors which restrict plant growth in arid or irrigated areas has produced notable contributions to the literature of this field in the past two decades. Quantitative information on the salt tolerance of the most important crop plants has been obtained, and the proximal causes of salt injury have, in some cases, been carefully analyzed. Experimental demonstration of the general occurrence of osmotic effects and the more restricted development of specific ion effects has cleared the way for further advances in understanding the nature of salt injury to plants. Still awaiting clarification is the relative importance of factors which contribute to salt tolerance or sensitivity when osmotic effects predominate. It is obvious that when water availability is restricted by salinity, all the factors which regulate or influence water absorption and water loss by plants contribute in some way to the resultant which is termed 'salt tolerance.' Little has, as yet, been done to evaluate these factors in terms of their contribution to salt tolerance. The mechanisms whereby chloride or sodium ions are specifically toxic to sensitive species remain unknown. The similarity of toxic levels of accumulation of these ions in widely diverse species suggests a common mechanism or condition which qualitatively distinguishes these species from non-sensitive species. The mechanism of salt toxicity, and the distinguishing features of salt tolerance, appear to be the major tasks for research on salt tolerance of plants in the decade ahead. [ABSTRACT FROM AUTHOR]