Parts and Structure of a Leaf

Introduction

Photosynthesis and transformation are followed by the two main functions of the leaf. In a few plants, it also embraces the responsibility of reproduction. 

Leaf 

The greeny, thin and flattened organs that are responsible for photosynthesis in the plant are known as, leaves. A leaf is developed laterally or branch borne at a node. They have a bud in their axil. They hold a significant part in the shoot system. it is mainly originated from shoot apical meristems.  

Characteristics of a Leaf

A few characteristics or traits of a leaf are given below :

1. It is always borne at the node of the stem. 

2. An axillary bud is always present in the axil of a leaf. 

3. It is exogenous in origin developing from the swollen leaf primordium of the growing apex.

4. It develops in an acropetal order over the stem, i.e, produced one after other from base to apex. 

5. Leaf lamina is traversed by prominent vascular strands which are called veins. 

The Structure of the Leaf

The leaf structure consists of each leaf which typically has a leaf blade ( lamina ), stipules, a midrib, and a margin. Some leaves have a petiole, which attaches the leaf to the stem; leaves that do not have petioles are directly attached to the plant stem and are called sessile leaves. Each leaf typically has a leaf blade ( lamina ), stipules, a midrib, and a margin. 

Parts of  Leaf 

A typical leaf has three main parts are as follow:

1.  Hypopodium (Leaf Base)

The part of lead attached to the stem or a branch is called the leaf base. It is consists of different types: 

i. Pulvinus :

 When the leaf has a swollen leaf base, it is called a pulvinus. If the bases of the leaflets are swollen they are known as a pulvinus.

 Example – Mango

 ii. Sheathing :

 The leaf blade becomes broad and flat and covers some parts of the stem in monocots. 

 Example – Banana, Maize, and Sugarcane

iii. Amplexicaul : 

The sheathing leaf base clasps and surrounds the stem. 

Examples – Polygonum, Aethusa, Wheat. 

iv. Semi-amplexicaul :

The stem is partially enclosed by leaf base. 

Example – Ranunculus and Palms. 

v. Decurrent :

Petiole and leaf base, both of them become broad, flat, and winged. 

Example – Symphytum, Laggera, etc. 

vi. Articulate : 

The stem is partially enclosed by the ones of the leaf bases. 

Example – Calotropis

2. Mesopodium (Petiole)

It connects the lamina with the stem or branch. Petiole helps in exposing the leaf blade to sunlight. A leaf is called to be sessile. If the people are absent. 

Example – wheat, rice,  Calotropis, Glorisoa, etc. 

When petiolate is a present example – peepal, mango, guava, etc. 

3. Epipodium (Leaf blade or lamina) 

The most important, green, and flattened part is the leaf which is mainly concerned with the manufacture of food. Lamina is traversed medically from the base of the apex by the midrib from which arise numerous thin lateral veins, and still thinner veins or veinlets.

Venation

The arrangement of venue and veinlets in the leaf lamina is called Venation. There are two types of venation :

1. Reticulate Venation : 

They are found in dicot leaves. In this type of vacation, the main vein divides into branches to form a net structure in the lamina. 

2.  Parallel Venation :

All veins run parallel to each other. The monocot leaves have this type of venation. 

Stipules 

The lead base bears two lateral appendages called the stipules and leaves are called stipulate. It provides protection. 

The leaves without stipules are called exstipulate. In monocots, an extra outgrowth is presently called ligule and such leaves are called ligulate.  

Example – Shoe-flower.

The different types of stipules on their basis of position, shape, colour, and size are as follow: 

1. Foliaceous : 

The two large, green, and leafy structures. Examples – Pea and Wild pea 

2. Free lateral : 

The two, small, green, free stipules are present on lateral sides of the leaf base. Example – China rose

3. Adnate :

The two lateral stipules are attached to the petiole up to some distance but the anterior part remains free. Example – Rose, groundnut, etc.

4. Interpetiolar :

The stipules lie between the two leaves at nodes. Example – lxora, hamelia, etc. 

5. Ochreate : 

Both the stimulus of the leaf make a hollow tube that encircles the stem up to the upper part of the node.  Example – Polygonum

6. Spinous :

The stipules are adapted into two shared pointed structures. They are the defensive organs of the plant. It gives protection to the leaf against searching animals. Example – Acacia

7. Tendrillar :

The stipules were modified into tendrils. Example – Smilax

8. Intrapetiolar : 

Both stipules join in the inner margin and look like single stipules. Example – Gardenia

9. Bud Scales :

The stipules are mainly observed in young leaves of Banyan and ficus. They fall off as soon as the leaves unfold. 

10. Scaly: 

The very small, dry, and membranous stipules.

Example – Cassia fistula

Conclusion

Hence, we can say leaves manufacture organic food by the process of photosynthesis. This is accomplished due to the presence of green pigment (chlorophyll). Stomata present on the leaf surface helps in the exchange of gases necessary for photosynthesis and respiration. It does assist transpiration which helps in the ascent of sap and also keeps the leaf surface cool. The vascular elements in the veins and petiole help in the conduction of water and minerals from the stem to the lamina and organic food from the lamina to the stem.