Corn and tomato plants were grown in a series of expts. with their roots divided between 2 or more solns. of unequal conc. Irrespective of whether the differences in conc. were produced by the addition to the base nutrient of chloride, sulfate, or additional nutrient salts, the growth of roots in and the water up-take from the dilute soln. were > that from the conc. one, indicating that osmotic pressures, rather than specific ion effects, are primarily involved. The wt. of the new corn roots in a 0.3 atm. soln. was 1.6 times and water uptake was 3 times that in a 1.8 atm. soln. In a parallel expt., the position of the roots in the dil. and conc. solns. was alter-nated each 2d day to produce 2 sets of roots of equal wt. With these roots the water uptake from the dilute soln. was twice as great as that from the cone. soln. Roots divided between distilled water and conc. nutrient made more growth in the''latter; during the first 3 days water uptake was greatest from the distilled water but later from the conc. soln. A substantial movement of Cl" and other ions through the roots from conc. to dil. sols. was found. 15- to 60-fold variations in the cones. of SO4= and Cl" respectively are shown within the root zone of single irrigated orange trees.