5.63). The abaxial epidermis consists of a single layer of compactly arranged rectangular transparent paren­chymatous cells. It makes up the green tissue of the leaf and consists of thin-walled cells containing chloroplasts (bits that contain the chlorphyll). The epidermis is usually one cell layer thick. =>If found in … The vascular bundles are generally found at the boundary between the palisade and the spongy regions. It is 2 to 3 layered, with compactly arranged tubular cells, rich in parietal chloroplasts. In Poinsettia (= Euphorbia pulcherrima) the young leaves are brightly coloured to attract insects for pollination. Leaf base may be broadened to enclose the stem. The mesophyll is typically separated into two different types of materials called palisade and spongy parenchyma. 2. Typically it is a thin expanded green structure which bears a bud in its axil. The rachillae are arranged in a pinnate fashion on the Primary axis or rachis, e.g., Acacianilotica (vern. 5.61 C) and Nepenthes (Fig. Instead petiole and part of the rachis become flattened into sickle-shaped structure for performing the function of food synthesis (Fig. Each leaf typically has a leaf blade ( lamina ), stipules, a midrib, and a margin. The epidermis consists of compactly arranged oval rectangular transparent parenchy­matous cells. Reticulations are absent. It forms the main bulk of leaf and includes parenchyma which Is differentiated into two regions: i. Palisade Tissue: It is made-up of one or two layers of closely arranged columnar cells. The leaf apex gives rise to a coloured lid for attracting the insects. Sieve tubes conduct organic food. The cuticle reduces the rate of water loss from the leaf surface. The principal veins diverge towards the mar­gins, e.g., Castor (Ricinus), Luffa, Vitis (Grape Vine), etc. Compound leaves may be palmate or pinnate. The most important structure on a leaf's lower epidermis is the mouth-shaped opening called the stoma. Succulent leaves occur in plants of saline and xerophytic habitats, e.g., Aloe, Agave, Bryophyllum, Portulaca. Depending upon the number of the leaflets present, a palmate compound leaf is called: (i) Multifoliolate or digitate (five or more leaflets, present at the tip of petiole, Fig. The mesophyll layer is divided into palisade and spongy layers. The leaflets or pinnules are borne on tertiary axes (Fig. These needle-like leaves have sunken stomata and a smaller surface area, two attributes that aid in reducing water loss. The primary function of the palisade parenchyma of a leaf is to host most of the chloroplasts in the plant, which is where photosynthesis occurs. Stipules are fused from their outer margins to become opposite the leaf, e.g., Castor. There are two basic forms of leaves that can be described considering the way the blade (or lamina) is divided. Each vascular bundle is surrounded by a single sheath of compactly arranged parenchyma cells called border parenchyma or bundle sheath. Any peculiarity of shape, size, and colour including variegation of leaves is picked up by horticulturists for propagation. For this a large sub-stomatal cavity lies below each stoma. 4. In a compound leaf, the leaf blade is divided, forming leaflets that are attached to the middle vein, but have their own stalks. Stipules are fused from their inner margins to become axillary, e.g., Gardenia. Trichomes: Trichomes give leaves a fuzzy appearance as in this (a) sundew (Drosera sp.). Anatomically there can be three types of leaves— dorsiventral (bifacial), isobilateral (equifacial) and unifacial. Leaf morphology is employed in taxonomy for accurate description, identification and classification of plants. (i) Pinnate or Unicostate Reticulate Venation: The lamina has a single principal vein or midrib which extends from its base to apex. Two leaves are borne on the opposite sides of a single node. In dicots, however, the veins of the leaf have a net-like appearance, forming a pattern known as reticulate venation. Leaves protect the axillary and terminal buds from mechanical injury and desiccation. The adaxial surface is the upper surface of a leaf. October 23, 2013. They enclose large cavities or intercellular spaces which are connected with the atmosphere through the stomata. Protection against transpiration by changing into phyllodes (expanded petioles) and forming spines. In Poinsettia (= Euphorbia pulcherrima, vern. Both layers of the mesophyll contain many chloroplasts. The arrangement of veins and veinlet’s on the lamina of a leaf is called venation. Palisade cells contain the largest number of chloroplasts per cell, which makes them the primary site of photosynthesis in the leaves of those plants that contain them, converting the energy in light to the chemical energy of carbohydrates. 5.61 G). (viii) A leaf is differentiated into three parts— leaf base, petiole and lamina. The various functions of the epidermis are: (iii) Loss of water vapours or transpiration through stomata, (iv) Reducing the rate of surface transpiration by the presence of cuticle, (v) Reducing the rate of transpiration by forming a stationary layer of air with the help of hair. It is the arrangement of leaves on the stem or its branches (Gk. (adsbygoogle = window.adsbygoogle || []).push({}); Most leaves have similar essential structures, but differ in venation patterns and leaf arrangement (or phyllotaxy). 58 E), e g Fennel Coriander (vern. 12. The palisade mesophyll consists of chloroplasts with chlorophyll that absorb the light energy. 6.36): The isobilateral monocot leaves usually do not show a distinction into petiole and lamina. The green colour of the leaf is due to the presence of chlorophyll. Masur) the tip of the rachis is transformed into a tendril. 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