Leaves :

1. A leaf is a dissimilar, green, flat, expended lateral outgrowth of stem or its branches on a node.
2. Each leaf consists of three parts i.e. leaf base or Vagina, petiole and lamina.
3. Leaf base is the lowermost part of the leaf by which it is attached with the node of stem.
4. Petiole is the stalk of leaf. The leaf blade or lamina is the expended green part which is supported by venis.
5. The major functions of the leaves are :

1. Photosynthesis
2. Gaseous exchange
3. Transportation

Parts of leaf

  Parts of leaf :

1. The green food making leaves of plants are termed foliage leave.
2. A typical foliage leaf consists of leaf stalk or petiole, expended portion at the end of petiole is called blade or lamina.
3. Leaf base is the lowermost part of leaf by which leaf is attached with node.
4. In some cases leaf base becomes swollen to form pulvinus.
5. In some species of plants leaf base forms small green appendage called stipule at the points of juncture of petiole with stem.
6. A leaf with stipules is called stipulate and without stipules, ex- stipulate.
7. Lamina in most of plants is flat, thin and broad with conspicuous system of veins and veinlets.
8. Lamina is usually  traversed by a prominent vein in the middle called as midrib.
9. The entire network constituted by midrid, veins and veinlets in leaf blade is called venation.
10. The side of lamina forms the margin and tip forms the leaf apex. The functions of leaf are:

1. It forms the food by the process of photosynthesis.
2. It helps in gaseous exchange during respiration.

Water loss occurs through stomata in leaves by transpiration.

Venation:

The arrangement and distribution of venis and veinlets in the leaf lamina is called venation.

There are three type of venation:

1. Reticulate venation: When the veins are  irregularly distributed to form a network, it is known as reticulate venation.
2. Parallel venation: When the veins are parallel and do not form a network, such a venation is called parallel.
3. Furcate venation: Such type of venation is present in ferns. In such cases veins divide dichotomously. The finer branches do not meet to form a reticulum or network.