Created by: Swati Sinha 1 year, 3 months ago
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Introduction to Anatomy of ...
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Anatomy of Dorsiventral Leaf

A study of the vertical section of dorsiventral leaf reveals the structure as follows:

Epidermis: The upper and lower surface of leaf is bound by upper and lower epidermis respectively.

Upper Epidermis: contains a single layer of barrel shaped living cells that usually have chloroplast. Cuticle forms a distinct outer surface on the epidermis which prevents excessive transpiration and protects internal cells against mechanical injury.

Lower epidermis: is formed from a single layer of packed rectangular living cells .A layer of cuticle is also present on the lower epidermis. There are a large number of pores called stomata present on the lower surface. Each stoma contains a narrow pore surrounded by guard cells. The guard cells possess chloroplasts and their inner conclave walls are greatly thickened. In many leaves, guard cells are surrounded by specialised epidermal cells known as accessory or subsidiary cells. Stomata have a dual role to play – in exchange of gases and in transpiration. Since, in dorsiventral leaves the stomata are present only on the lower epidermis, these leaves are also called as hypostomatic leaves.

Mesophyll is the ground tissue of the leaf and lies between the upper and lower epidermis layers. It is a green parenchymatous tissue and can be differentiated into two distinct regions – upper layer of palisade parenchyma and lower layer of spongy
parenchyma.

Palisade parenchyma occurs below the upper epidermis and contains columnar closely packed cells forming 1-3 layers at right angle to the upper epidermis. They may have small intercellular spaces. Since they are abundant in chloroplast, they attribute a dark green colour to the upper surface of leaf. Palisade parenchyma is the main photosynthetic tissue of plant.

Spongy parenchyma is positioned between palisade parenchyma and lower epidermis. The cells are unevenly shaped and have large intercellular spaces in between. These large intercellular spaces and the smaller intercellular spaces of the palisade parenchyma allow free movement of air within the leaf’s internal structure. Few chloroplasts may be present in spongy parenchyma. 

Vascular system contains multiple vascular bundles of different sizes. Vascular bundles are generally located in the boundary between palisade and spongy parenchyma. Bundle sheath, a sheath formed of compactly arranged parenchyma cells surrounds each vascular bundle. Each vascular bundle is conjoint and collateral. Xylem lies towards the upper side of the leaf whereas phloem lies towards the lower
surface. Cambium is absent. Xylem parenchyma stores food and allows lateral
movement of sap.

A few layers of schlerenchyma may be found on the outside of vascular bundle, mainly on the upper side just above the xylem. They provide mechanical support.
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Anatomy of Isobilateral Leaf
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