A stipule, present on the leaves of many dicotyledons, is an appendage on each side at the base of the petiole, resembling a small leaf. Red anthocyanin pigments are now thought to be produced in the leaf as it dies, possibly to mask the yellow hue left when the chlorophyll is lostâyellow leaves appear to attract herbivores such as aphids. External leaf characteristics, such as shape, margin, hairs, the petiole, and the presence of stipules and glands, are frequently important for identifying plants to family, genus or species levels, and botanists have developed a rich terminology for describing leaf characteristics. Upper epidermis Lower epidermis Chloroplast Air Space Guard cell Stoma Cuticle Vein Palisade mesophyll Cuticle Spongy mesophyll 8. Not every species produces leaves with all of these structural components.  In parallel veined leaves, the primary veins run parallel and equidistant to each other for most of the length of the leaf and then converge or fuse (anastomose) towards the apex. Sage et al. They grow to a specific pattern and shape and then stop. The lamina is the expanded, flat component of the leaf which contains the chloroplasts. 3. In general, parallel venation is typical of monocots, while reticulate is more typical of eudicots and magnoliids ("dicots"), though there are many exceptions. The mesophyll layer is divided into palisade and spongy layers.  Optical masking of chlorophyll by anthocyanins reduces risk of photo-oxidative damage to leaf cells as they senesce, which otherwise may lower the efficiency of nutrient retrieval from senescing autumn leaves. The Role of Anthocyanins in Senescing Leaves of Red-Osier Dogwood", "Classification of the Architecture of Dicotyledonous Leaves", "The Bases of Angiosperm Phylogeny: Vegetative Morphology", "Influence of light availability on leaf structure and growth of two, "Shoot and compound leaf comparisons in eudicots: Dynamic morphology as an alternative approach", "The Role of Elastic Stresses on Leaf Venation Morphogenesis", "Venation patterns of neotropical blueberries (Vaccinieae: Ericaceae) and their phylogenetic utility", "Evolution and Function of Leaf Venation Architecture: A Review", "Leaf Vascular Systems in C3 and C4 Grasses: A Two-dimensional Analysis", "The Pea Key: An interactive key for Australian pea-flowered legumes", Institute of Food and Agricultural Sciences, International Code of Nomenclature for algae, fungi, and plants, International Code of Nomenclature for Cultivated Plants, International Association for Plant Taxonomy, https://en.wikipedia.org/w/index.php?title=Leaf&oldid=995743523#Mesophyll, Short description is different from Wikidata, All Wikipedia articles written in American English, Wikipedia indefinitely move-protected pages, Articles with unsourced statements from April 2019, Pages using multiple image with manual scaled images, Pages using multiple image with auto scaled images, Wikipedia articles incorporating a citation from the 1911 Encyclopaedia Britannica with Wikisource reference, ÐÐµÐ»Ð°ÑÑÑÐºÐ°Ñ (ÑÐ°ÑÐ°ÑÐºÐµÐ²ÑÑÐ°)â, Srpskohrvatski / ÑÑÐ¿ÑÐºÐ¾Ñ ÑÐ²Ð°ÑÑÐºÐ¸, Creative Commons Attribution-ShareAlike License, Even; with a smooth margin; without toothing, Saw-toothed; with asymmetrical teeth pointing forward, With deep, wave-like indentations; coarsely crenate, Indented, with the indentations not reaching the center, Long-pointed, prolonged into a narrow, tapering point in a concave manner, Ending in a sharp, but not prolonged point, With a sharp, elongated, rigid tip; tipped with a cusp, Indented, with a shallow notch at the tip, Mucronate, but with a noticeably diminutive spine, All veins aligned mostly with the midvein, All veins branching repeatedly, net veined, Veins coming from the center of the leaf and radiating toward the edges, Tertiary veins running perpendicular to axis of main vein, connecting secondary veins, Other specialized leaves include those of, Alternate leaves have an angle of 180Â° (or . In many aquatic species, the leaves are submerged in water. They capture the energy in sunlight and use it to make simple sugars, such as glucose and sucrose, from carbon dioxide and water. Wild-type poplars (Populus tremula x P. alba). When the leaf is shed, it leaves a leaf scar on the twig.  Long narrow leaves bend more easily than ovate leaf blades of the same area. 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. There are more in the palisade cells than in the spongy mesophyll.  Each subsequent branching is sequentially numbered, and these are the higher order veins, each branching being associated with a narrower vein diameter. Cells are with large inter cellular space. 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. Reptiles such as some chameleons, and insects such as some katydids, also mimic the oscillating movements of leaves in the wind, moving from side to side or back and forth while evading a possible threat. The veins in a leaf represent the vascular structure of the organ, extending into the leaf via the petiole and providing transportation of water and nutrients between leaf and stem, and play a crucial role in the maintenance of leaf water status and photosynthetic capacity.They also play a role in the mechanical support of the leaf. The number of chloroplast in a single mesophyll cell ranges from 1 to 50. The chloroplasts in these cells absorb a major portion of the light energy used by the leaf. At the same time water is being transported in the opposite direction. Why would horses from North America settle in southern Russia? Leaves are normally extensively vascularized and typically have networks of vascular bundles containing xylem, which supplies water for photosynthesis, and phloem, which transports the sugars produced by photosynthesis. Because Mesophyll is ground tissue that occurs between the two epidermal layers. They may be subdivided into whether the veins run parallel, as in grasses, or have other patterns. These cells possess large concentration of chloroplast. The leaves and stem together form the shoot. The meaning of several of the following terms can overlap. , Leaves also function to store chemical energy and water (especially in succulents) and may become specialized organs serving other functions, such as tendrils of peas and other legumes, the protective spines of cacti and the insect traps in carnivorous plants such as Nepenthes and Sarracenia. Update: Thank You ATP-Man! 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. Some sawflies similarly roll the leaves of their food plants into tubes. ... Palisade cells are column shaped and packed with many chloroplasts. Spongy mesophyll cells are covered by a thin layer of water and loosely packed. Both are embedded in a dense parenchyma tissue, called the sheath, which usually includes some structural collenchyma tissue. They were once thought to be typical examples of pattern formation through ramification, but they may instead exemplify a pattern formed in a stress tensor field.. Although not as nutritious as other organs such as fruit, leaves provide a food source for many organisms. List the layers of the leaf starting at the upper cuticle all the way to the lower cuticle. It is composed of many layers of loosely arranged, spherical or oval chlorenchyma cells. Compare the number of chloroplast in the cells of the palisade mesophyll with the number in the cells of spongy mesophyll? Analyses of vein patterns often fall into consideration of the vein orders, primary vein type, secondary vein type (major veins), and minor vein density. Minor veins are more typical of angiosperms, which may have as many as four higher orders. A modified form of the Hickey system was later incorporated into the Smithsonian classification (1999) which proposed seven main types of venation, based on the architecture of the primary veins, adding Flabellate as an additional main type. Usually, many smaller minor veins interconnect these primary veins, but may terminate with very fine vein endings in the mesophyll. A number of authors have adopted simplified versions of these schemes. Leaves almost always have determinate growth. True leaves or euphylls of larger size and with more complex venation did not become widespread in other groups until the Devonian period, by which time the carbon dioxide concentration in the atmosphere had dropped significantly.  The conspicuousness of veins depends on a number of features. In the series, the numerator indicates the number of complete turns or "gyres" until a leaf arrives at the initial position and the denominator indicates the number of leaves in the arrangement.  Hydrostatic leaves such as in Prostanthera lasianthos are large and thin, and may involve the need for multiple leaves rather single large leaves because of the amount of veins needed to support the periphery of large leaves. The cylindrical shape of palisade cells allows a large amount of light to be absorbed by the chloroplasts. The mesophyll, consisting of upper and lower palisade layers and median spongy mesophyll, contains cluster crystals about â¦ Veins (sometimes referred to as nerves) constitute one of the more visible leaf traits or characteristics. In this regard, veins are called obscure and the order of veins that are obscured and whether upper, lower or both surfaces, further specified. The adaxial palisade mesophyll comprises relatively regular, cylindrical cells, whereas much less regularly shaped cells make up the more porous spongy mesophyll. The leaves of bryophytes are only present on the gametophytes, while in contrast the leaves of vascular plants are only present on the sporophytes, and are associated with buds (immature shoot systems in the leaf axils). This occurred independently in several separate lineages of vascular plants, in progymnosperms like Archaeopteris, in Sphenopsida, ferns and later in the gymnosperms and angiosperms. A leaf (plural leaves) is the principal lateral appendage of the vascular plant stem, usually borne above ground and specialized for photosynthesis. Spongy cells of the leaf are loosely packed together and lie between the palisade and the lower epidermis with the air spaces connected to each other and the outside by stomata. Suppose there were many chloroplast in the cells of the upper epidermis. Some species have cryptic adaptations by which they use leaves in avoiding predators. Perennial plants whose leaves are shed annually are said to have deciduous leaves, while leaves that remain through winter are evergreens.  Veins may show different types of prominence in different areas of the leaf. 2012). :445, The internal organization of most kinds of leaves has evolved to maximize exposure of the photosynthetic organelles, the chloroplasts, to light and to increase the absorption of carbon dioxide while at the same time controlling water loss. Most leaves show dorsoventral anatomy: The upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions. In turn, smaller veins branch from the secondary veins, known as tertiary or third order (or higher order) veins, forming a dense reticulate pattern. Open: Higher order veins have free endings among the cells and are more characteristic of non-monocotyledon angiosperms. In most plants, leaves also are the primary organs responsible for transpiration and guttation (beads of fluid forming at leaf margins). The cells of the bundle sheath of many -especially tropical- graminaceous plants are enclosed by a wreath of chloroplast-containing mesophyll cells (called Kranz anatomy; Kranz (german) = wreath). 21.10E, F). In cold autumns, they sometimes change color, and turn yellow, bright-orange, or red, as various accessory pigments (carotenoids and xanthophylls) are revealed when the tree responds to cold and reduced sunlight by curtailing chlorophyll production. Both cell layers surround the vascular bundles -if seen in cross-section- like two concentric rings. 3. The epidermis tissue includes several differentiated cell types; epidermal cells, epidermal hair cells (trichomes), cells in the stomatal complex; guard cells and subsidiary cells. How would that change the amount of sunlight reaching the chloroplasts in â¦ Strong wind forces may result in diminished leaf number and surface area, which while reducing drag, involves a trade off of also reducing photosynthesis. These distinct lineages exhibit unique aspects that highlight their independent evolution from C3 ancestors. Females of the Attelabidae, so-called leaf-rolling weevils, lay their eggs into leaves that they then roll up as means of protection. 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. However, the leaf may be dissected to form lobes, but the gaps between lobes do not reach to the main vein. The sugars are then stored as starch, further processed by chemical synthesis into more complex organic molecules such as proteins or cellulose, the basic structural material in plant cell walls, or metabolized by cellular respiration to provide chemical energy to run cellular processes. Petiolated leaves have a petiole (leaf stalk), and are said to be petiolate. The concentration of photosynthetic structures in leaves requires that they be richer in protein, minerals, and sugars than, say, woody stem tissues.  The epidermis serves several functions: protection against water loss by way of transpiration, regulation of gas exchange and secretion of metabolic compounds. Leaves can show several degrees of hairiness. The middle vein of a compound leaf or a frond, when it is present, is called a rachis. Sage et al.  Thus, minor veins collect the products of photosynthesis (photosynthate) from the cells where it takes place, while major veins are responsible for its transport outside of the leaf. Spongy mesophyll cells are a type of parenchyma cells which is a part of the mesophyll tissue or ground tissue present below the epidermis of leaves in plants. , There are also many other descriptive terms, often with very specialized usage and confined to specific taxonomic groups. Of materials is usually in opposite directions, are called areoles the shed may! Normal inside or a frond, when it is composed of many layers of loosely arranged, or. 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