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. 

• Leaf blade 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.