Leaf Surface Morphology Research Articles

OVIPOSITION PREFERENCE OF HOMALODISCA COAGULATA FOR TWO CITRUS LIMON CULTIVARS AND INFLUENCE OF HOST PLANT ON PARASITISM BY GONATOCERUS ASHMEADI AND G. TRIGUTTATUS (HYMENOPTERA: MYMARIDAE)

Oviposition preference of Homalodisca coagulata (Say) and two of its mymarid egg parasitoids, Gonatocerus ashmeadi Girault and G. triguttatus Girault, for two Citrus limon L. cultivars (‘Eureka’ and ‘Lisbon’) was investigated. In laboratory oviposition choice tests, the number of leaves containing H. coagulata egg masses, the number of H. coagulata egg masses, and the total number of H. coagulata eggs were significantly higher at 187.2%, 204.2%, and 181.7%, respectively, on ‘Eureka’ versus ‘Lisbon’. In the field, there was no significant difference in the number of H. coagulata motiles counted in five-minute searches of foliage on ‘Eureka’ and ‘Lisbon’ trees, and numbers of leaves with old (emerged) and new (unemerged) H. coagulata egg masses were equivalent between field-planted cultivars. In the laboratory, parasitism of H. coagulata egg masses by G. ashmeadi and G. triguttatus was 18.6% and 23.2% higher, respectively, for eggs laid on ‘Eureka’ leaves compared to ‘Lisbon’, but these differences were not significant. Leaf surface morphology and thickness of leaf cell layers of both lemon cultivars were compared with scanning electron microscopy (SEM). SEM demonstrated that total leaf thickness and the thickness of the palisade layer was 19.2% and 38.6% higher, respectively, in ‘Eureka’ leaves compared to ‘Lisbon’, and that H. coagulata egg placement was between the lower epidermis and spongy parenchyma layer for both cultivars. Furthermore, ‘Lisbon’ leaves had a smooth underside, whereas ‘Eureka’ leaves had many small ridges. The thickness and rough surface of ‘Eureka’ leaves may be beneficial for H. coagulata oviposition. However, additional research is required to further investigate whether leaf characteristics or xylem chemistry are responsible for H. coagulata oviposition choice. For mass rearing programs with lemons as host plants, it is recommended that the ‘Eureka’ cultivar be used in preference to ‘Lisbon’ because H. coagulata prefers this cultivar for oviposition and parasitoid foraging is not adversely affected.

A study of differentiation patterns in Capparis sect. Breyniastrum in Cuba, with a nomenclatural and taxonomic survey of Cuban Capparis (Capparaceae)

Abstract Rankin Rodriguez, R. & Greuter, W.: A study of differentiation patterns in Capparis sect. Breyniastrum in Cuba, with a nomenclatural and taxonomic survey of Cuban Capparis (Capparaceae). — Willdenowia 34: 259–276. — ISSN 0511-9618; © 2004 BGBM Berlin-Dahlem. Capparis is represented in Cuba by six species of four sections. A key for their identification is provided, their nomenclature and that of the sections in which they belong is revised, and the intricate relevant typification problems are discussed. Three species, each of a different section, are not critical taxonomically. The other three, which belong to C. sect. Breyniastrum, have been poorly understood and often confused in the past. Microcharacters of trichome and leaf surface morphology (illustrated by SEM photographs) prove useful to tell them apart. In conclusion, two Macroantillean species are recognised, each represented in Cuba by a distinct, endemic subspecies (one new, one recombined); a third species, C. singularis, known from a...

Scanning Electron Microscopy of Leaves of Southern Live Oak

Yadong Qi* and Ying Xiao** *Urban Forestry Program, Southern University and A&M College, Baton Rouge LA 70813 **Department of Biology, Louisiana State University, Baton Rouge LA 70803 Southern live oak (Quercus virginiana Mill.) is a large evergreen broadleaf tree species that has significant landscape values in the U.S. This species is considered a virtual emblem of the Old South. Very little information is available regarding the leaf anatomy of the tree. This paper presents the scanning electron microscopy (SEM) of leaf gross morphology and anatomical features of live oak. The information will contribute to our better understanding of the physiology and morphology, tree growth and development of this species. Sun-exposed leaves were collected from mature southern live oak trees on Southern University campus in the end of June. Leaves were prepared for scanning electron microscopy. They were dissected, fixed in FAA (Ethanol, Glacial Acetic Acid, and Formaldehyde), dehydrated in an ethanol series, and dried in carbon dioxide using Denton DCP-1 critical point drying apparatus. Leaves were mounted on stubs, coated with 25 nm gold palladium using a Hummer II Sputter Coater, and examined using a Cambridge S-260 scanning electron microscope. The scanning electron micrographs of southern live oak leaves are illustrated in FIG. 1. The abaxial surfaces of the leaves are covered with a thick layer of trichome with multicellular peltate (shield-shaped) structure (FIG. 1a). A secretory function has been attributed to this type of leaf hairs [1]. A fully developed individual trichome shows as many as seventeen long narrow cells that are fused together for nearly half of their length. The surfaces of the trichome cells form a distinctive type of cuticle morphology, in which the outer surface is thrown into warty projections (FIG. 1b), indicating reinforced cell walls. This type of cuticle reinforcement was also reported in the leaf hairs of goosegrass (Galium aparine) [2]. The stomata are only presented on the abaxial surface and are generally covered up by the trichome. On the top of the guard cells around the stomatal aperture is cuticle serving as a primary protective layer in addition to the trichome layer (FIG. 1c). The adaxial leaf surface morphology is significantly different from the abaxial surface (FIG. 1d). The adaxial surfaces have no trichome at all and are smoothly covered by the cuticle and wax. The leaf transverse structure shows that the palisade tissue consists of three layers of compacted parenchyma cells (FIG. 1e). The thick trichome layer and closely packed palisade tissues are significant features of southern live oak leaves. The trichome layer functions as a mechanical barrier against biotic attack, an additional resistance to the diffusion of water vapor from leaf interior to the atmosphere, a reflector reducing the radiant energy absorbed by the leaf, and an absorber to help screen out harmful UV-B radiation from the sun. The closely packed palisade cells enhance photosynthesis efficiency by increasing photosynthetic sites and surface area of leaf interior. Thus, these leaf anatomical features provide southern live oak with specific eco-physiological advantages. Reference [1] J.H. Troughton and F.B. Sampson, Plants, John Wiley & Sons Australasia Pty Ltd, 1973. [2] B.S. Gunning and M.W.Steer, Plant Cell Biology Jones and Bartlett Publishers, 1996.

Correlations between leaf structural traits and the densities of herbivorous insect guilds

The functional composition of herbivorous insect assemblages was correlated with aspects of new and mature leaf surface features, anatomy and morphology across 18 co-occurring plant species. Multivariate analyses of insects and leaf traits revealed that the functional composition of the herbivore assemblage was more strongly correlated with leaf structural traits than with leaf constituents. Leaf traits were more strongly correlated with the functional composition of the herbivore assemblage than with its taxonomic composition. Densities of sessile phloem feeders, rostrum chewers, and all herbivores were significantly negatively correlated with specific leaf weight, lamina and cuticle thickness, vascular tissue depth and stomate length, and were significantly positively correlated with stomate density. External chewer densities were significantly negatively correlated with percent lignified vein area, and significantly positively correlated with leaf surface area and the distance between lignified tissues. Spine-like leaves were associated with significantly lower densities of sessile phloem feeders, external chewers and all herbivores compared to kite leaves (kite leaves are comprised of unfortified leaf tissue supported by a framework of vascular tissue). The presence of a thickened leaf hypodermis was associated with significantly lower densities of external chewers and rostrum chewers, while midrib protection was associated with significantly lower densities of external chewers. Leaf structural traits may not be the proximal factors influencing herbivorous insects, as leaf structural traits are correlated with many other plant traits such as photosynthetic rate, relative growth rate and leaf life-span. Nonetheless, these results indicate that certain leaf structural traits may potentially be used to predict the functional structure of herbivorous insect assemblages.

Cuticular waxes of Arabidopsis.

Cuticular waxes of Arabidopsis.

Comparative Study of Oak Species for Intercepting Particle Pollution

Trees can act as efficient biological filters to remove significant amounts of particulate pollution from urban atmospheres (Nowak, et al. 1994 ). Recent controlled environment studies have indicated that tree's ability in intercepting and removing particle pollution varies among species. Studies by Abdollahi et al. (2000) confirmed that there were significant differences among different tree species in intercepting particle pollution. Live Oaks (Quercus virginiana), River Birch ( Betula nigra),and Sugar hackberry (Celtis occidentalis) are statistically more efficient at capturing pollutant particles of less than 2.5 microns (PM2.5) than tree species such as Red Maple (Acer Rubrum),Southern Magnolia (Magnolia grandiflora),and Sycamore (Platanus occidentalis).Other Studies also suggested that the leaf surface morphology of these trees might play an important role in interception and removal of PM2.5.The main objectives of this study were to quantify the relative ability of selected oak species (Quercus spp.) in removing particle pollution of less than 2.5 microns (PM2.5) and to characterize oak leaf surface morphology.

Seasonal fluctuations in the concentration of UV-absorbing compounds in the leaves of some Mediterranean plants under field conditions.

Leaves of 14 representative Mediterranean plant species were collected on a monthly basis and assayed for UV-absorbing compounds concentration, either on an area or a dry mass basis, from 1995 to 1997. Strong seasonal fluctuations were observed in eight species (all evergreens, two phrygana, one deciduous, one summer perennial and one winter perennial). Two different patterns of changing concentrations of UV-absorbing compounds were observed. In the first, concentration of these compounds was higher in young developing leaves and concentration declined during maturation, whereas in other plants, the opposite trend was observed. These differences could be attributed to the particular leaf surface morphology of each plant. The observed seasonal fluctuations of UV-absorbing compounds seem to be more correlated to developmental processes, than to seasonal fluctuations of the naturally occurring UV-B radiation. Most of the winter perennials did not show strong fluctuations during the period of development. The concentration of these compounds varied not only on a seasonal basis among the examined plants, but between different life forms as well: during winter, examination of the leaves of 13 species showed that evergreen sclerophylls and phrygana had at least two-fold higher concentration of UV-B-absorbing compounds on a leaf area basis than winter perennials. In addition, during the same season and irrespective of life form and species, the absorbance at 300 nm per unit of mature leaf area followed an asymptotic exponential decrease when specific leaf area increased. The UV-B radiation screening capacity of the leaves of these plants is discussed in relation to each adaptive strategy.

Effect of culture media and irradiance level on growth and morphology of Persea americana Mill microcuttings

Avocado shoots were multiplied in vitro in two culture media of different consistency, double phase and solid medium, at three different irradiance levels: 35, 60 and 85 µmol m −2 s −1 . Effects of culture and environmental conditions in multiplication rate, rooting capacity, hyperhydricity and leaf surface morphology of microcuttings were evaluated. Double phase medium induced hyperhydricity, producing leaf microcuttings with deformed stomata and low crystalline epicuticular waxes; microcuttings also showed reduced rooting capacity. By contrast, solid medium promoted leaf area development on microcuttings and decreased hyperhydricity. Stomatal index was not affected by these treatments but stomatal density was, interacting with the amount of irradiance applied. Increasing irradiance decreased concentration of chlorophyll a and carotenoids in the leaf but did not affect leaf hyperhydricity.

Apple and Peach Leaf and Stem Surface Morphology and Soybean Oil Retention as Influenced by Simulated Rainfall and Soybean Oil Emulsions

Environmental factors such as rainfall may reduce the efficacy of foliar-applied soybean [Glycine max (L.) Merrill] oil in reducing pest mortality. Greenhouse studies were conducted to investigate the influence of rain on the retention of soybean oil and the influence of soybean oil and rainfall on surface morphology of apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] and peach [Prunus persica (L.) Batsch (Peach Group)] leaves and stems. `Contender' peach and `Golden Delicious'/Malling 27 apple trees were grown in 19 L pots in a greenhouse (23 ± 9 °C) and sprayed with soybean oil (1%) emulsified with the adjuvants Latron B-1956 or K1. Twenty-four hours after treatment, the trees were subjected to simulated rainfall of 0.0, 0.25, 1.25, or 2.54 cm. A negative linear relationship existed between rainfall and oil retention. Peach leaves receiving 0.25, 1.25, and 2.54 cm rainfall retained 81%, 38%, and 18% of the applied oil, respectively. Oil retention by apple leaves was also negatively related to rainfall. For both species, a negative linear relationship existed between oil retention on stems and rainfall. There was no effect of emulsifier on retention of 1% soybean oil after rain on apple leaves or on the retention of 8% to 11% soybean oil on the stems of apple and peach. Scanning electron microscopy revealed that epicuticular wax occurred as striations on apple and peach leaves. The wax morphology on peach and apple stems appeared as thin plates and platelets, respectively. The wax morphology of leaves and stems of both trees was not affected either by the soybean oil emulsions or rain. Both emulsions induced stomatal closure in leaves and peach stems, however, stomates opened after rainfall of 1.25 or 2.54 cm. The lenticels appeared to be unaffected by either emulsion. Results illustrate that rainfall of 2.54 cm washed off a major portion of the applied oil. Thus, respraying may be needed under natural climatic conditions with rainfall ≥2.54 cm to restore the efficacy of applied soybean oil.

Leaf Surface Morphology of Urban Tree Species and Its Contribution to Particle Pollution Removal

Abstract According to the findings by the National Resource Defense Council (NRDC), dust, soot, and many particles in polluted air over the nation's 239 major cities cause 64,000 of premature heart and lungrelated deaths each year. In light of the new reports, the Environmental Protection Agency (EPA) has announced the plan to impose tougher restrictions to include fine particulate less than 2.5 microns (PM2.5). The new regulations could cost more than $2.5 billion a year to implement in a city like Chicago alone. Urban trees as a component of urban ecosystem can provide cost effective phyto-mitigation and phyto-remediation strategy for improving urban environment and quality of life. Previous studies have indicated that trees in Chicago removed 234 tons of particulate matter less than 10 microns (PM10) annually. To the extend that trees can control particulate pollution there is potential for improved air quality and substantial cost savings.

Alterations of Leaf Epicuticular Wax of Peanut (Arachis hypogaea) by Applications of Herbicides and Adjuvants1

Abstract Leaf surface morphology of untreated peanut leaves and peanut leaves treated with herbicides and adjuvants were examined using scanning electron microscopy. Electron micrographs revealed that the adaxial surface of untreated peanut leaves was covered with crystalline wax platelets above an amorphous layer of wax. Electron micrographs revealed that peanut leaves treated with acifluorfen plus nonionic surfactant, bentazon and lactofen with crop oil concentrate, and 2,4-DB, altered the leaf surface morphology when compared to nontreated peanut leaves. Alterations in the leaf epicuticular wax structures appeared amorphous-like rather than normal plate-like structures. Nonionic surfactant and crop oil concentrate applied alone to peanut leaves altered the epicuticular wax structures similarly to that of herbicides plus adjuvants.

Wild Aloe harvesting in South Africa.

The Journal of Alternative and Complementary MedicineVol. 5, No. 2 PhotoessayWild Aloe Harvesting in South AfricaHassan Sachedina and Dr. Gerard BodekerHassan SachedinaSearch for more papers by this author and Dr. Gerard BodekerSearch for more papers by this authorPublished Online:24 Sep 2007https://doi.org/10.1089/acm.1999.5.121AboutSectionsPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetailsCited byCape aloe bitters – past and presentSouth African Journal of Botany, Vol. 147Analysis of enablers for vertical integration to enhance rural employabilityJournal of Business & Industrial Marketing, Vol. 34, No. 4Aloe Genus Plants: From Farm to Food Applications and Phytopharmacotherapy19 September 2018 | International Journal of Molecular Sciences, Vol. 19, No. 9Micropropagation of Aloe vera for Improvement and Enhanced Productivity8 November 2013Research on Water Soluble Polysaccharides Separated from Skin Juice, Gel Juice and Flower of Aloe ferox MillerFood Science and Technology Research, Vol. 19, No. 5African aloe ecology: A reviewJournal of Arid Environments, Vol. 85Current perspectives on the economic botany of the genus Aloe L. (Xanthorrhoeaceae)South African Journal of Botany, Vol. 77, No. 4Taxonomic significance of leaf surface morphology in Aloe section Pictae (Xanthorrhoeaceae)Botanical Journal of the Linnean Society, Vol. 160, No. 4Therapeutic uses of Aloe L. (Asphodelaceae) in southern AfricaJournal of Ethnopharmacology, Vol. 119, No. 3Growth of Aloe ferox Mill. at selected sites in the Makana region of the Eastern CapeSouth African Journal of Botany, Vol. 73, No. 2 Volume 5Issue 2Apr 1999 InformationCopyright 1999, Mary Ann Liebert, Inc.To cite this article:Hassan Sachedina and Dr. Gerard Bodeker.Wild Aloe Harvesting in South Africa.The Journal of Alternative and Complementary Medicine.Apr 1999.121-123.http://doi.org/10.1089/acm.1999.5.121Published in Volume: 5 Issue 2: September 24, 2007PDF download

Ultrastructural changes caused by post-emergence herbicides in leaves of bengal wandering jew (Commelina benghalensis L.)

The leaf surface morphology of C. benghalensis and the ultra structura I changes in C. benghalensis leaves caused by herbicide treatments in combination with adjuvants were studied with electron microscopes. The study indicated u It ra structural changes in treated leaves. All treatments caused changes in infrastructure in parenchyma cells. Three days after treatment, thylakoids in parenchyma cells were swollen and disrupted chloroplast envelopes were visible. The chloroplasts appeered swollen and were spherical in shape and also lacked starch grains.

Anatomical and morphological parameters of leaves and leaf petioles of Actinidia deliciosa

Differences in anatomy and morphology of the kiwifruit leaves and leaf petioles might play a considerable role in the sex-determination. Three months after bud break (June), the kiwifruit leaves of both male and female plants, grown on the vegetative and generative shoots showed different leaf area (128.6 ± 13.45 cm2 in male and 104.5 ± 4.02 cm2 in female plants) and shape. The most frequently leaf shape was determined as folium cordatum and folium rotundato-cordatum. Higher values of total leaf thickness of the female leaves (190 ± 3.84 µm) in comparison to male leaves (174 ± 3.52 µm) were estimated, resulting in the thicker adaxial leaf epidermis and especially in thicker palisade parenchyma in female leaves (136 ± 2.76 µm in comparison to 104 ± 1.61 µm in male leaves). Typically bifacial leaves were observed in both male and female leaves. Anomocytic stomata in hypostomatic leaves were found. The reticulate venation appears to be the main type of leaf venation. Stalked stellate multicellular trichomes on the abaxial leaf side were frequently observed in the leaves of both sexes. No important differences between male and female plants were found in the structures of vascular system in leaves and leaf petioles. Thus leaf thickness and surface morphology of adaxial leaf epidermis can be considered as important structural parameters in the sex determination.

Foliar Nitrogen Fertilization of Citrus in Florida

Foliar applications of urea nitrogen (N) is a relatively new practice in Florida citrus production resulting from applied research and changes in citrus fertilizer management philosophy. The present study investigated the effect of leaf age and surface morphology on leaf wettability as measured by contact angles, and absorption efficiency of foliar-applied N. Young leaves (0.25 and 1 month) were more efficient than old leaves in the absorption of foliar-applied N. Contact angles of water, urea-, and triazone-N solutions were low in the young leaves. The adaxial surfaces had lower contact angles than abaxial surfaces in each leaf age group. Inefficient N absorption and large contact angles in old leaves (3 and 6 months) were related to surface wax deposition and cuticle thickness, which increased with leaf age. 15N- and 14C-labeled urea are being used to determine precisely how the cuticle and wax affect foliar N absorption in citrus leaves.

Influence of light intensity and water stress on leaf surface characteristics of Cynoglossum officinale, Centaurea spp., and Tragopogon spp.

Leaf surface characteristics of Cynoglossum officinale, Centaurea diffusa, Centaurea maculosa, Tragopogon dubius, and Tragopogon pratensis, important rangeland weeds of Canada, and effects of light intensity and water stress on these characteristics were studied using scanning electron microscopy. Both adaxial and abaxial leaf surfaces of Cynoglossum officinale were covered with long, uniseriate trichomes with extensive micropapillate sculpturing. The leaf surfaces of Centaurea diffusa and Centaurea maculosa had two types of trichomes: (i) sparsely distributed, multicellular, uniseriate trichomes with ribbon-like chloroform–ether soluble extensions at their tips and (ii) glandular trichomes. Centaurea diffusa and Centaurea maculosa cannot be distinguished on the basis of trichome morphology. No crystalline epicuticular wax was observed on Cynoglossum officinale or Centaurea spp. leaf surfaces. Cynoglossum officinale and Centaurea diffusa uniseriate trichomes became more abundant as light intensity declined. Micropapillate sculpturing on Cynoglossum officinale trichomes disappeared at low light intensities. Ribbon-like extensions at the tips of Centaurea diffusa uniseriate trichomes increased with increase in soil moisture stress. The leaf surfaces of Tragopogon dubius and Tragopogon pratensis lacked trichomes but were covered with tubular epicuticular wax. Tragopogon dubius and Tragopogon pratensis cannot be distinguished on the basis of epicuticular wax morphology. The abundance and size of epicuticular wax crystals on the adaxial leaf surface of Tragopogon pratensis declined with decrease in light intensity and increased with increase in soil moisture stress. Such plasticity of leaf surface morphology may be important in the acclimation of these species to harsh environments. Key words: epicuticular wax, light intensity, moisture stress, scanning electron microscopy, trichomes, weeds.

Leaf Surface Morphology of Erythroxylum sp. and Droplet Spread

Studies were conducted to examine the micromorphology of leaf surfaces of coca and nova plants and to determine which spray diluents provided optimum coverage of leaf surfaces. Adaxial leaf surfaces of both species were covered with a smooth layer of polygonal-shaped epidermal cells which were covered with wax crystals. Abaxial leaf surfaces were composed only of papillae cells and the guard and subsidiary cells surrounding stomata. Abaxial leaf surfaces of both species were also covered with wax crystals. Average wax weights were 28 to 53 μg cm−2. Water droplets containing an organosilicone surfactant at 0.1% by vol spread better on leaf surfaces that did other adjuvants. Droplets of several different petroleum-based oils spread much better on leaf surfaces than either water droplets with adjuvants or droplets of soybean or cottonseed oil.

Taxonomic significance of epidermal morphology in Nigerian Rhizophoraceae

SUMMARY Epidermal morphology of adaxial and abaxial leaf surfaces of five genera of the family Rhizophoraceae in Nigeria were studied by light microscopy. The epidermises are composed of variously shaped cells which, in surface view, range in outline from triangular, rectangular to more commonly hexagonal, polygonal and irregular. Cuticular striations are absent except in Poga oleosa in which conspicuous striae encircle the guard cells and run parallel to the axis of non-specialized epidermal cells. Anticlinal walls are either straight, curved or undulate. Leaves of all genera are hypostomatic. Paracytic stromata occur in Cassipourea and Anisophyllea while all species of Rhizophora possess cyclocytic stomata. The stomata of Anopyxis are of the anisocytic type and those of Poga anomocytic. The morphology of the guard cells and stomatal ledges varies significantly within the family. Evidence is produced to support the suspected hybrid nature of Rhizophora harrisonii. Other features of the epidermis that show variation include stomatal size, shape and density, size and density of epidermal cells, and cell wall thickness. Epidermal characters are of some utility in elucidating relationships and identifying some taxa within the family.

Pecan Cultivar Susceptibility to Sooty Mold Related to Leaf Surface Morphology

Sooty mold washed from leaves of four cultivars of pecan [Carya illinoensis (Wangenh.) C. Koch] was quantified. The amounts of sooty mold accumulation differed significantly (P ≤ 0.05) among the cultivars. Leaf surface morphology of each cultivar was examined. A higher incidence of sooty mold was associated with cultivars having a rough, granulated leaf topography than those with smoother leaf surfaces. Characteristics of leaf surface morphology may be useful in selecting germplasms with reduced susceptibility to sooty mold accumulation.

Herbicide Deposition on Leaf Surfaces

Leaf surface morphology and physical characteristics of herbicide deposits on leaf surfaces can influence herbicide performance. Leaf surface topography, the degree and type of epicuticular wax formation, and the presence, type, and distribution of trichomes all influence the distribution of a given herbicide formulation sprayed onto a leaf surface. Depressions above anticlinal cell walls accumulate herbicide, thus lessening uniform distribution. As the amount of particulate wax increases, the size of individual spray drop deposits on the leaf decreases, thus resulting in reduced coverage. In many instances the presence of trichomes reduces optimal epidermal coverage by intercepting spray drops before they reach the epidermal surface. Adjuvants reduce the adverse influence of leaf topography, epicuticular wax, and trichomes on herbicide distribution, but their use usually does not yield an even coating over the entire leaf surface. Many herbicides, in pure form, are solids (i.e., crystals) rather than liquids. For most applications, herbicides are dissolved, dispersed, or emulsified in a water-based spray solution. After spraying, water and any solvents evaporate from the leaf surface and herbicides often return to their solid crystalline form. In the few cases that have been studied, less herbicide is absorbed when present on the leaf surface as a solid rather than as a liquid. In many instances, greater effectiveness of a postemergence herbicide may be obtained if attention is given to optimizing the distribution and physical form on sprayed leaf surfaces.