Lesson 8 of 10 · 6 min
Dorsiventral leaf
NCERT §6.2.5, Figure 6.5
Meera wedges a mango leaf in a slit carrot, slices across it and gets a thin strip. The top half of the strip is packed with tall green cells; the bottom half looks like a sponge.
The lesson in notes
In short
A dicot leaf is dorsiventral. A vertical section through the lamina shows three parts: epidermis, mesophyll and vascular system.
Upper surface = adaxial epidermis; lower surface = abaxial epidermis. Both carry a conspicuous cuticle.
The abaxial (lower) epidermis usually has more stomata than the adaxial one, which may have none.
Mesophyll is the parenchyma between the two epidermal layers. It contains chloroplasts and carries out photosynthesis.
Palisade parenchyma lies on the adaxial side: long cells standing upright, side by side.
Spongy parenchyma lies below the palisade and reaches the lower epidermis: oval or round cells loosely packed with many large spaces and air cavities.
Vascular bundles run in the veins and midrib, and their size matches the size of the vein. Dicot veins vary in thickness because the venation is reticulate.
A sheath of thick-walled cells rings each bundle. Xylem lies towards the upper (adaxial) side of the bundle and phloem towards the lower side.