Leaf: Structure and Venation Patterns by BHS aakash

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Leaves are the primary photosynthetic organs of plants. They are attached to the stem/branch through the leaf base, supported by the petiole, and expanded into the lamina. The arrangement of veins on the lamina is called venation. Let’s look at each part in detail.


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1. Leaf Base

The leaf base is the part of the leaf that attaches to the stem or branch.

Pulvinus: A swollen leaf base found in legumes.

Leaf sheath: The base expands and partly or wholly encloses the stem (e.g., grasses).

Stipule: Small, leaf-like structures at the leaf base.

If present → the leaf is stipulate (e.g., pea).

If absent → the leaf is exstipulate.




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2. Petiole

A hard stalk-like structure that connects the lamina to the stem.

Functions:

Holds the leaf in air to capture light.

Increases transpiration by exposing lamina.




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3. Lamina

The largest and most important part of the leaf.

Functions:

Main site of photosynthesis.

Performs gas exchange and transpiration.


Parts include: apex, margin, and midrib.



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4. Venation

Venation is the arrangement of veins and veinlets in the lamina.

(a) Reticulate Venation

Veins form a network-like pattern.

Common in dicots.

Examples: Peepal, Mango.


(b) Parallel Venation

Veins run parallel without forming a network.

Common in monocots.

Examples: Banana, Sugarcane, Grass.



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Quick Recap

Leaf base: Pulvinus, sheath, stipules.

Petiole: Supports lamina, increases transpiration.

Lamina: Main photosynthetic part.

Venation: Reticulate (dicots) vs. Parallel (monocots).

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