Relation of Stomatal Penetration to Herbicidal Effects Using Fluorescent Dye as a Tracer

and Summary. Plants of Zebrina pendula L., Phaseolus vulgaris L., Sorghum halepense (L.) Pers., and Chenopodium album L. were sprayed with a solution containing herbicide (sodium 2,4-dichlorophenoxyacetic acid or sodium 2,2-dichloropropionic acid), surfactant (sodium dioctylsulfosuccinate), and fluorescent tracer (sodium pyrenetrisulfonate). In most instances plants having stomata relatively open absorbed more tracer (based on UV observation) and more herbicide (based on injury and growth responses) than those with stomata relatively closed. Differences, however, were less than those expected from studies using detached leaves, prob- ably from poorer control of stomatal aperture in intact leaves. There was good agreement between degree of opening and tracer uptake. T HE exact routes by which chemicals applied to leaves 1 are absorbed are not known. Those who are concerned with the foliar application of chemicals, such as her- bicides, have debated the question of the relative im- portance of the stomatal versus the cuticular components of absorption.