Effects of Osmotic Concentration of Substrate on the Entry of Water into Corn Roots

Abstract

The entry of water into com roots was detd. quantitatively with a potometric device attached at 3 root levels; 2, 6 and 10 cm. from the root tip. Substrates of 3 osmotic conc. were used[long dash]0.8 (control), 2.8 and 4.8 atm. with NaCl as the added salt to the control soln. Tests were run on nonconditioned, preconditioned and decapitated plants. In general, the most rapid entry was in the zone between the 6- and 10-cm. levels. In all tests the rate was lowest at the 2-cm. level. 82% of control plants had the highest rate at the 10-cm. level. The state of maturity of the vascular, endo-dermal, hypodermal and epidermal tissues affects rate of entry. Increased maturity of vascular and epidermal tissues increases entry of water; increased maturity of endodermal and hypodermal tissues and disintegration of epidermal tissue decreases it. Substrates of high osmotic pressure inhibit meristematic activity and elongation of the root, and under these conditions the zone of most rapid entry is nearer the root tip. With both nonconditioned and preconditioned roots high osmotic pressure of substrate significantly reduced rate of entry. At corresponding root levels and in substrates of equal conc., preconditioned plants had higher rates than nonconditioned ones. As compared with intact plants, decapitated plants exhibited marked reduction in entry rate in all substrates and at all root levels except at the 2-cm. level in the high salt solns.