Question

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

Answer 1

1. Upper epidermis: This is often the parenchymatous cell-based outermost single layer. Papillae are occasionally seen as outgrowths of the epidermal cells, as in the case of Gladiolus. The top epidermis lacks stomata and the epidermal cells lack chloroplasts.
2. Lower epidermis: The latter may even lack stomata. The tissue between the upper and lower epidermis is called the mesophyll. Mesophyll, which possesses chloroplasts and carries out photosynthesis, is made up of parenchyma.
3. Mesophyll: In between the upper and lower epidermis, mesophyll tissue is present, which can be divided into two regions:
   1. Palisade parenchyma: These are lengthy, columnar cells with no intervals between them. They are often divided into two layers and include chloroplasts.
   2. Spongy parenchyma: It is found below palisade parenchyma and are spherical or oval with intercellular spaces. They also have chloroplasts but number of chloroplasts is more in palisade parenchyma than spongy parenchyma.
4. Vascular bundles: It is typically located at the border where the spongy areas and the palisade meet. The midrib region contains the greatest vascular bundle. Vascular bundles are closed, conjoint, and collateral. Every vascular bundle has a bundle sheath made up of parenchymatous cells around it. Phloem is found in the vascular bundle towards the lower epidermis, whereas xylem is present towards the upper epidermis. Protoxylem is next to the top epidermis in the xylem.