Permeability of Apricot Leaf Cuticle.

Altlhoughl cutimize(d tissue in some forlmi is the first harrier to the entrv of chemicals into plants, dlirect measurements of the permeability properties of cuticular membranes are limited aandl qualitative (1, 5 ). Froml clirect miieasuremleints oin isolated cuiticle Skoss (9 ) has reported that Eniglish ivy leaf cuticle is relativelv illmpermleable to w ater, aandl that lemloni leaf cuticle is impermeable to the sodiunm salt of 2,4-dichlorophenoxyacetic acid, to the ammiioolniunm salt of dIinitro-o-sec-but lplleinol. andl to silver and chloriOle ionls. Similarly Orgell (7 ) hlas reported little, if any, penetration of isolated apricot leaf cuticle bv "polar solutes in a(queous solutioni, e.g. acids, bases, salts, (IN-es, and miniscellanieouis otlher conllpoullis. Adding to these hiis oWln o)servation that oils (lo not penetrate the upper cuticle of apricot leaves (11), van Overbeek (12) conclucledl that penetration of leaf cuticle by clhelmiicals is unlikely. MIitchell, Snmale, and \IMetcalf (5), hlov-ev-er, accepting that cuticle in some forml covers the enitire aboveground surface of the plant. concludledl that hydrated cuticle is permneable to a (legree to water an(l to (lissolveel compounds associatedl -with tlis water, and is highly permleable to nolnpolar compoundis. The objectives of this x-ork xvere to (luaintitativelv niieasure penetration througlh stomata-free isolated leaf cuticle andl attempt to assess the imlportanice of this entry pathwx av in intact plantsto imieasure the effect of substitueint variation oni penetration 1w the nmodlel conmpouncl a-clhloroacetanmide (ClCH.,CONH.,'; aiad to seek a correlation betxveen peinetratiotIand chloroform-water plartitioning that imlighlt allowx a prediction of leaf penetration rates of other Coml l)ounds.