Growth of Cotton Seedlings in Relation to Maximum Daily Plant‐Water Potential 1

A pressure chamber technique was used to evaluate the relation between leaf‐water potential (leaf Ψ w ) and growth of cotton ( Gossypium hirsutum L.) seedlings under greenhouse conditions. A water potential gradient of about 5 bars developed from plant top to bottom by early afternoon, but disappeared after several hours of darkness. A diurnal change of about −12 bars occurred during one day of a drying cycle. Maximum leaf Ψ W were reached just prior to sunrise. Growth processes depending largely on cell expansion for expression were affected at identical water deficits during the drying cycle. Increases in plant height, in leaf area, and in fresh weight were inhibited when potentials above −8 bars were not reached for a portion of each day. Predawn wilting was not observed until the eighth and final day of the stress period, corresponding to a leaf Ψ W of −26 bars.