SUMMARYEffects of simulated rain on the epicuticular wax of glaucous leaves have been studied. Droplets (250 to 400 fim) travelling at low or medium velocity (0 25 to 5 m s'^) fractured the dendrites and tubes on leaves of Brassica spp., the tubes on Eucalyptus globulus Labillardere and the ribbons on the adaxial surfaces of Pisum sativum L. and Fragaria ananassa Duchesne. Rates of erosion for Brassica and E. globulus leaves were high during an initial application equivalent to 1 mm rainfall but declined markedly with extended exposure. In contrast, erosion from P. sativum and F. ananassa proceeded at a fairly uniform rate throughout the exposure period. The composition of the detached wax deposits was identical with that of the intact leaf wax for Brassica species but differed for the other species. The practical consequences of wax erosion of field crops are considered.
Seasonal changes in the surface waxes of the leaves and fruits of four species of Citrus have been examined. Leaf wax deposits ranging from 20pg/cm2 in orange to 31 pg/cm2 in lemon were consistent during all except the most juvenile stages of growth whereas the surface waxes of the fruits showed considerable variation, the most pronounced being a 58% decrease in the wax deposits of lemon between July and October. Hydrocarbons (23-66 %), primary alcohols (6-38%) and fatty acids were important constituents of the waxes of mature leaves and fruits but aldehydes present as major components of the fruit waxes (28-44%), were found only in trace quantities in the leaf waxes. n-Hentriacontane and n-tritriacontane, the dominant homologues of the hydrocarbon fractions were the major components of the leaf waxes which also contained n-hexacosanol and n-octacosonal as important constituents. n-Nonacosane, n-hentriacontane, n-tetracosanal, n-hexacosanal and n-octacosanal were present in the largest proportions in the fruit waxes.
SUMMARYChanges in surface properties during expansion of the leaves of eight plant species have been examined in relation to the uptake of 1-naphthylacetic acid. Rates of wax production ranged from 01 ng cm"^ h"^ for sugar beet leaves to 6-2 nm cm"^ h~^ for leaves of Eucalyptus globulus. Individual leaves of all species maintained difFerent rates of wax production at their adaxial and abaxial surfaces. Rates of synthesis of wax fractions and their constituent homologues varied with surface and leaf age. The homologue distribution shifted towards components of longer chain length as the leaves expanded. Morphological changes in wax deposits were small and limited largely to increases or decreases in the density of the plate waxes. Rates of penetration of 1-naphthylacetic acid varied between species, between leaf surfaces and with age of tissue. The highest rates of uptake were confined to the period when the leaves expanded most rapidly. The decrease in penetration rate with increase in age of the tissue, common to most plants, was greatest for grape vine and Eucalyptus globulus leaves both of which maintained high rates of wax production during expansion.
The effects of cuticular properties on the impaction and redistribution of aqueous and oil solutions, emulsions and wettable powders were studied using a microapplicator, which dispensed monosize droplets (50‐400 μm), and a range of techniques including scanning electron microscopy, X‐ray analysis and microautoradiography. Lateral and transcuticular movement of active ingredients was monitored by stripping the outermost wax layers and adhering deposits with cellulose acetate films applied as a spray from an acetone solution. Spread factors, determined using fluorescent markers and a reflectance microscope, varied extensively. Oil formulations spread rapidly through layers of crystalline wax whereas aqueous solutions distributed most readily over smooth surfaces. An X‐ray analyser attachment to the scanning electron microscope proved particularly useful for investigating the complex interactions occurring between plant surfaces and diluted e. c. and w. p. formulations. Kamaps and elemental spectra confirmed that lipophilic materials partitioned preferentially into the organic phase which separated as a zone at the outer edge of the droplet residue, whereas water‐soluble compounds concentrated in the central region.
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