. Explain Leaf and its Parts
1. The leaf is a lateral, generally flattened structure borne on the stem.
2. The leaves develop from the nodes.
3. Their main function is photosynthesis.
4. Axillary buds are found in its axil, which later develops into a branch.
5. Leaves originate from shoot apical meristem and are arranged in acropetal order.
Leaf is divided into three parts:
1. Leaf base (Hypopodium)
2. Leaves are attached to stem by leaf base.
3. In some plants, leaf base becomes swollen and is called pulvinus which is responsible for sleep movement , e.g., Cassia, Mimosa, Bean.
4. In monocot plants, leaf base expands into sheath covering the stem partially or wholly (Sheathing leaf base), e.g., grasses and banana (monocots).
1. The part of leaf connecting the lamina with the branch of stem. Petiole helps to hold the blade towards light. In Eichhornia petiole swells up and in Citrus it is winged.
2. Petiole is modified into tendrils in Nepenthes.
3. In Australian Acacia petiole is modified into phyllode.
4. Long, thin and flexible petiole allows leaf blade to flutter in air, thereby, cooling the leaf and bringing fresh air to leaf surface.
Lamina (Epipodium) - It is a broad and flattened green part of the leaf. Its main functions are photosynthesis and transpiration.
1. Lamina contains vein and veinlets.
2. Middle prominent vein is known as the mid-rid.
3. Vein provides rigidity to the leaf, and acts as channel of transport for water, mineral and food.
4. The shape, margin, apex, surface and extent of incision of lamina varies in different leaves.
1. Leaves of some plants have lateral appendages on either side of the leaf base, known as stipules. If stipules are present in leaf it is called stipulated leaf, if it is absent then leaf is called exstipulated.
2. Foliaceous These type of stipules form a leaf like structure. E.g., Pea.
3. Tendrillar Stipules are modified into tendril like structure. E.g., Smilax.