CONTROLLING TRANSPIRATION IN ASPEN WITH PHENYLMERCURIC ACETATE

A 0.001 M spray of phenylmercuric acetate was applied by helicopter to part of an aspen stand in northern Utah in June, 1967. The natural fluttering action of the aspen leaves facilitated delivery of the spray to the stomate‐bearing underside of the leaves. Nine days after treatment, stomate width on treated trees averaged 2.4 μ as compared with 4.0 μ measured on untreated trees. Heat pulse measurements indicated reduction in daylight sap velocity from 11 cm/hr to 6 cm/hr. Seasonal soil moisture depletion was not significantly affected, although the pattern of water usage was delayed for about 6 weeks on the treated area. Copyright 1969 by the American Geophysical Union.