What is Leaves its Definition, structure, venation and phyllotaxy | study science

Leaves

 Definition

The leaves is lateral, flattened structure borne on stem. Leaves develops at the node and bear a bud in its axil.
-Leaves originate from shoot apical meristem. They are the most important vegetative organ for photosynthesis

 

Structure of leaves

Generally, a leaf consist of 3 main parts, leaf base, petiole, and lamina (leaf blade)

 Leaves parts

1. Leaf base - leaf base  help in the attachment of leaves to the stem. Small leaf like structures are present at the leaf base which is called stipule

 

* Leaf base expand into sheath covering in monocotyledons plant.

* Leaf base become swollen and called pulvinus in leguminous plant.

2. Petiole - it is long, thin, stalk, that links leaf blade to stem. It help to hold the leaf blade towards light.

3. Lamina ( leaf blade) - The green flat surface of the leaves with vein and veinlet are called lamina.
Lamina is also known as leaf blade.

 

Venation

The arrangement of veins and the vein let in the leaves is called venation.

 *Different plant show different type of venation. 

Leaves usually have a middle prominent vein which is known as midrib.

*Two types of venation is generally seen in leaves.

1. Reticulate
2. Parallel

1. Reticulate venation - when veinlets form a network it is called reticulate venation.
 Eg: Dicotyledonous plant

 

2. Parallel venation - when vein run parallel to each other with a lamina it is called parallel venation.
Eg: Monocotyledons plant

 * Vein present in the leaves provide rigidity to leaf blade.
 * Vein act as a channel of transport for water mineral and food material. 

Phyllotaxy

 The patterns of arrangement of leaves on the stem are called phyllotaxy.

 

*Plants show three types of phyllotaxy:

1. Alternate 

2.Opposite

3.Whorled

 

1. Alternate phyllotaxy - when only a single leaf develops at each node in alternate manner, It is called alternate phyllotaxy.

Eg: China rose, mustard

2.Opposite phyllotaxy - when a pair of leaves develops at each node opposite to each other, it is called opposite phyllotaxy.

Eg: Calotropis, guava plant

 

3. Whorled phyllotaxy - if more than two leaves arise at a node and form a whorl.

     Eg: Alstonia