Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.

Explanation

The internal structure of a monocot leaf ( isobilateral leaf ) shows 3 main parts , namely 1 . Epidermis , 2. Mesophyll and 3. Vascular bundles .
1 . Epidermis : Epidermis is present on both the upper surface (adoxial ) and the lower surface (obaxial ) of the leaf . The epidermis is made up of barrel shaped cells which are arranged compactly without intercellular spaces . The cells are filled with vacuolated cytoplasm and possess a single nucleus but chloroplasts are absent . Epidermal hairs are absent . Epidermis is externaly hairs are absent . Epidermis is extenaly covered by a waxy layer called cuticle . The number of stomata on both the sides is almost equal . In some monocots like grasses some cells of upper epidermis are enlarged and specialised , called Bulliform cells or Motor cells . They are thin walled and are filled with water . They help in rolling and unrolling of the leaf . The epidermis gives protection to the inner tissues , regulates the transpiration and helps in gaseous exchange .
(2) . Mesophyll : It is present between the upper and lower epidermal layers . It is made up of several layers of columnar cells or spongy cells , that are loosely arranged showing intercellular spaces . They contain chloroplasts . the mesophyll is the chief photosynthetic tissue of the leaf .
(3) Vascular bundles : Numerous vascular bundles are present in the mesophyll in the form of veins . The vascular bundles are conjoint , collateral and closed . Xylem is present towards upper side and phloem towards lower side .
Each vascular bundle is enclosed by a layer of specialised mesophyll cells called border parenchyma or bundle sheath . Sometimes , bundle sheath is composed of dead scierenchymafous tissue . the bundle sheath cells divide and grow towards both the sides of the vascular bundle . they are called bundle sheath extensions . They help in the conduction of materials from the mesophyll to the vascular bundle . They also give mechanical strength to the leaf .