This is the second of two articles on the quality of water and plant tolerance to salts. The previous article, in the October issue of California Agriculture, explained the classification of irrigation waters in three groups: Class I. Excellent to Good—Safe and suitable for most plants under any condition of soil and climate. Class II. Good to Injurious—Possibly harmful for certain crops under certain conditions of soil OT climate. Class III. Injurious to Unsatisfactory—Probably harmful to most crops and unsatisfactory for all but the most tolerant.