The leaflets may have petiolules and stipels, the equivalents of the petioles and stipules of leaves. [59], The terms megaphyll, macrophyll, mesophyll, notophyll, microphyll, nanophyll and leptophyll are used to describe leaf sizes (in descending order), in a classification devised in 1934 by Christen C. Raunkiær and since modified by others. [2] Leaves are collectively referred to as foliage, as in "autumn foliage". List the layers of the leaf starting at the upper cuticle all the way to the lower cuticle. [62] The conspicuousness of veins depends on a number of features. [10] These are interpreted as reduced from megaphyllous leaves of their Devonian ancestors. Leaves can have many different shapes, sizes, and textures. Of these, angiosperms have the greatest diversity. Many leaves are covered in trichomes (small hairs) which have diverse structures and functions. These can further develop into either vegetative or reproductive structures. The concentration of photosynthetic structures in leaves requires that they be richer in protein, minerals, and sugars than, say, woody stem tissues. For instance, the parallel venation found in most monocots correlates with their elongated leaf shape and wide leaf base, while reticulate venation is seen in simple entire leaves, while digitate leaves typically have venation in which three or more primary veins diverge radially from a single point. They may be subdivided as; Pinnate (feather-veined) leaves, with a main central vein or rib (midrib), from which the remainder of the vein system arises. However, horizontal alignment maximizes exposure to bending forces and failure from stresses such as wind, snow, hail, falling debris, animals, and abrasion from surrounding foliage and plant structures. [19] The terminology associated with the description of leaf morphology is presented, in illustrated form, at Wikibooks. The leaf is a vital source of energy production for the plant, and plants have evolved protection against animals that consume leaves, such as tannins, chemicals which hinder the digestion of proteins and have an unpleasant taste. Veins (sometimes referred to as nerves) constitute one of the more visible leaf traits or characteristics. Females of the Attelabidae, so-called leaf-rolling weevils, lay their eggs into leaves that they then roll up as means of protection. The epidermis is the outer layer of cells covering the leaf. Guard cells are the only epidermal cells to contain chloroplasts. The broad, flat leaves with complex venation of flowering plants are known as megaphylls and the species that bear them, the majority, as broad-leaved or megaphyllous plants. In clasping or decurrent leaves, the blade partially surrounds the stem. Many gymnosperms have thin needle-like or scale-like leaves that can be advantageous in cold climates with frequent snow and frost. [43], In the course of evolution, leaves have adapted to different environments in the following ways:[citation needed], May be coarsely dentate, having large teeth, or glandular dentate, having teeth which bear glands. The central mesophyll is sandwiched between an upper and lower epidermis. In either case, the shed leaves may be expected to contribute their retained nutrients to the soil where they fall. 1. Typically leaves are broad, flat and thin (dorsiventrally flattened), thereby maximising the surface area directly exposed to light and enabling the light to penetrate the tissues and reach the chloroplasts, thus promoting photosynthesis. Petiolated leaves have a petiole (leaf stalk), and are said to be petiolate. The stomatal pores perforate the epidermis and are surrounded on each side by chloroplast-containing guard cells, and two to four subsidiary cells that lack chloroplasts, forming a specialized cell group known as the stomatal complex. The slight separation of the cells provides maximum absorption of carbon dioxide. Stomata therefore play the important role in allowing photosynthesis without letting the leaf dry out. Less commonly, dicot leaf blades may have palmate venation (several large veins diverging from petiole to leaf edges). [3][4] In most leaves, the primary photosynthetic tissue, the palisade mesophyll, is located on the upper side of the blade or lamina of the leaf[1] but in some species, including the mature foliage of Eucalyptus,[5] palisade mesophyll is present on both sides and the leaves are said to be isobilateral. Why are there antibodies for both A and B? Plants that lack chlorophyll cannot photosynthesize. The leaf surface is also host to a large variety of microorganisms; in this context it is referred to as the phyllosphere. These distinct lineages exhibit unique aspects that highlight their independent evolution from C3 ancestors. What is the chief function of the epidermis of a leaf? Most leaves show dorsoventral anatomy: The upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions. Its cells contain many more chloroplasts than the spongy layer. The longest leaves are those of the Raffia palm, R. regalis which may be up to 25 m (82 ft) long and 3 m (9.8 ft) wide. [18] Stipules may be conspicuous (e.g. In many aquatic species, the leaves are submerged in water. Upper epidermis Lower epidermis Chloroplast Air Space Guard cell Stoma Cuticle Vein Palisade mesophyll Cuticle Spongy mesophyll 8. In turn, smaller veins branch from the secondary veins, known as tertiary or third order (or higher order) veins, forming a dense reticulate pattern. In contrast, spongy parenchyma is the lower mesophyll layer of spherical or ovoid cells with few chloroplasts and very prominent intercellular air spaces. They are vertically elongated, a different shape from the spongy mesophyll cells beneath them. Leaves can also store food and water, and are modified accordingly to meet these functions, for example in the leaves of succulent plants and in bulb scales. For instance Pimenta racemosa has a channelled midrib on the upper surfae, but this is prominent on the lower surface. Both cell layers surround the vascular bundles -if seen in cross-section- like two concentric rings. These three tissue systems typically form a regular organization at the cellular scale. When the leaf is shed, it leaves a leaf scar on the twig. Specialized cells that differ markedly from surrounding cells, and which often synthesize specialized products such as crystals, are termed idioblasts.[32]. Compare number of chloroplast in cells of palisade mesophyll w/number in cells of spongy mesophyll? A number of different classification systems of the patterns of leaf veins (venation or veination) have been described,[25] starting with Ettingshausen (1861),[46] together with many different descriptive terms, and the terminology has been described as "formidable". Hairs on the leaf surface trap humidity in dry climates and create a. ATP-Man. [41] Long narrow leaves bend more easily than ovate leaf blades of the same area. Epidermis is the “skin” of the leaves. Leaf sheathes typically occur in grasses and Apiaceae (umbellifers). The opening and closing of the stomatal aperture is controlled by the stomatal complex and regulates the exchange of gases and water vapor between the outside air and the interior of the leaf. Suppose there were many chloroplast in the cells of the upper epidermis. According to Agnes Arber's partial-shoot theory of the leaf, leaves are partial shoots,[37] being derived from leaf primordia of the shoot apex. Accordingly, leaves are prominent in the diet of many animals. Comments: Numbers extracted from figure 2D. Considerable changes in leaf type occur within species, too, for example as a plant matures; as a case in point Eucalyptus species commonly have isobilateral, pendent leaves when mature and dominating their neighbors; however, such trees tend to have erect or horizontal dorsiventral leaves as seedlings, when their growth is limited by the available light. Monocot mesophyll also tends to be more porous on the abaxial side, but with a gentler porosity gradient through the leaf depth (Mathers et al., 2018) (Fig. [14], Simple, vascularized leaves (microphylls), such as those of the early Devonian lycopsid Baragwanathia, first evolved as enations, extensions of the stem. Gases dissolve in this water as they move into and out of the cells. In the clubmosses, with different evolutionary origins, the leaves are simple (with only a single vein) and are known as microphylls. Early in development they are dorsiventrally flattened with both dorsal and ventral surfaces. [33] The epidermis serves several functions: protection against water loss by way of transpiration, regulation of gas exchange and secretion of metabolic compounds. What are the laws for paramotors in Aleialei Atoll. Overall leaves are relatively flimsy with regard to other plant structures such as stems, branches and roots. [23] This pattern is often specific to taxa, and of which angiosperms possess two main types, parallel and reticulate (net like). [20], Monocot leaves in temperate climates usually have narrow blades, and usually parallel venation converging at leaf tips or edges. Further classification was then made on the basis of secondary veins, with 12 further types, such as; terms which had been used as subtypes in the original Hickey system. Regular organization at the margin leaf surface trap humidity in dry climates and create a home... 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