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The present study. in which a comparison is made of the growth of Marquis wheat in sand and solution cultures, represents one of several experiments involving solution III of the National Research Council series which are now in progress in the plant-physiology laboratory at Iowa State College.Most investigators attempting to determine the salt requirements of higher plants have used water cultures. Tottingham (2S) placed the whole proposition on a definite quantitative basis. He took the well-known Knop's solution, and, by varying the proportions of salts under definite volume-molecular partial concentrations, procured a superior yield of wheat of II percent over the original solution.Shive (19) followed the plan suggested by Tottingharn' and, making use of a three-salt solution containing mono-potassium phosphate, calcium nitrate, and magnesium sulphate, obtained an increase in yield of wheat of 27 percent over Tottingham's solution of the same total concentration. McCall (10) used Shive's solution and grew wheat in sand cultures. He noted that the average dry weights of both tops and roots were decidedly greater for the plants grown in sand than for those grown in the solution cultures. Incidentally there was a marked difference between the solutions producing the highest yield of plants in sand and those giving the best growth in Shive's cultures.Livingston and Tottingham (8) made a preliminary test of a series of type III solutions, containing the three component salts KNO z , Ca(H 2P0 4 ) 2 , and MgS0 4 • Their results showed that the solution IIIR6CI was apparently just as good as Shive's best IRSC2 solution. However, this experiment lasted only 18 days.Shive (20) and Shive and Martin (22) studied the salt requirements of young and of mature buckwheat plants in both solution and sand cultures. They found that the solution yielding the maximum weight of tops during the early developmental period, and the solution that gave the highest yield of tops and of roots during the late period of development, were identical for both the solution and the sand cultures, but the actual dry weight of 1 Tottingham (25) has presented an extensive review of literature covering the subject of solution cultures. For citations see pages 242-245. 18

The status of the question of permanent wilting in plants, as described by Briggs and Shantz (5, 6, 7, 8), Caldwell (ii), Shive and Livingston (37), and Alway (i), centers about the determination made by Briggs and Shantz that a plant is regarded as having attained a condition of permanent wilting when it does not recover its turgidity in a period of 24 hours when surrounded by air saturated with water vapor. The method of