Leaf - Structure , types and modification

 

Leaf is an important part in plant. It perform the photosynthesis as well as bear stomata for gaseous exchange.

The leaf is green and flat structure present on stem. Biologically it is orignated from the node of stem and bear buds in its axil. This axillary bud in future is transformed into a new branch.

Leaf is developed from the activity of shoot apical meristem.  There are prominently   three part of a typical leaf - Leaf base, petiole and leaf lamina.

The leaf is attached with the stem by the  Leaf base also bear small leaf life appendages called stipules .

In Monocot plants like Maize and sugar cane , the leaf base is grow and make a cover for stem which cover stem completely or partially .

In legume plant like pea gram leaf base get swollen and form a structure called pulvinus.

The petiole help hold the leaf blade. Petiole allow the leaf blade to flutter in wind . By this activity of petiole, leaf get cooling and. Fresh air may enter into leaf surface.

Leaf blade also called leaf lamina. It is most expanded part of leaf and bear stomata. It also bear vein and veinlet. The thick and centrally located vein is termed midrib. Vein provide rigidity for the leaf blade.

👌👌Remember - vein act as channel for transport of water mineral and food material.

A leaf may be simple or compound. When incision or  cut portion  of leaf blade do not touch the mid rib than leaf is simple.

When incision or  cut portion  of leaf blade  touch the mid rib and leaf blade is divided into large number of leaflets  than leaf is compound.

Compound leaf may be pinnately or palmately. When leaflets are present on common rachis which may represent mid rib called pinnately compound leaf. For example - Neem.

When leaflets are originated from a common point at tip of petiole called palmately compound leaf.

When leaf perform other function like support, storage of food, protection, etc  than the photosynthesis called modification of leaf.

In Garden pea, leaf is modified into tendril for the climbing with the external support.

In Cactus and opuntia  leafs are modified into spines for the defense against browsing animal.

In Australian Acacia , leaves are short lived and its petiole become green to synthesized food.

In insectivorous plants like Napenthes or pitcher plant , Venus fly trap or Dionea the leaves are modified into a pitcher like structure to catch the and digest the insect. These plant digest insect to fulfil their nitrogen requirement.

In onion or Garlic, leaves are modified into swollen structure because it store food.