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What are the different Parts and Characteristics of Flower ?

The flower is the most attractive, brightly, coloured and conspicuous part of the plant. It helps in sexual reproduction and later forms fruit and seeds.

PARTS OF A FLOWER

The flower is attached with the stem or its branches with the help of a stalk called pedicel. If the flower is without pedicel, it is called sessile.
Different Parts of Flowers

The pedicel may arise from the axil of a green leaf- like structure called bract. Sometimes, the pedicel may bear two small, leafy, green bract-like structures called bracteoles. 

The other swollen end of the pedicel is the thalamus or torus. It represents a condensed shoot. On the thalamus usually four whorls of floral structures are present.

These four whorls from outer to inner side are :
  1. Calyx 
  2. Corolla 
  3. Androecium 
  4. Gynoecium. 
The first two whorls are non-essential floral parts whereas, the inner two whorls are essential parts which are involved in the process of reproduction. These floral structures are explained as follow :

Calyx (Sepals)

They constitute the outermost and lowermost whorl. They are mostly small, green, leaf-like structures which cover an unopened floral bud.

They protect inner whorls of the flower in the bud stage. In some cases, the sepals may be coloured like petals as in gulmohar (flame of forests). Such sepals are called petaloids.

The sepals present in the outermost whorl may be all fused or free from each other. Accordingly they are termed as follow :

(a) Gamosepalous - When all the sepals are fused together, fully or partially, they are termed as gamosepalous e.g. Sunflower, China rose, Marigold, Petunia etc.

(b) Polysepalous - When all the sepals are free from each other they are called polysepalous. e.g. Ranunculus, Brassica. 

Functions

  • They are primarily protective in function. They protect inner whorls the flower in the bud stage.
  • They can also synthesize food, as they contain chlorophyll.
  • They may also help in attracting insects, birds and other animals for pollination. Additional floral whorl outside the calyx is called epicalyx (e.g. Hibiscus).

Corolla

Petals, that constitute the second whorl are collectively called corolla. They arise inner to and above the sepals on thalamus. 

They are usually brightly coloured and showy leaf-like structures in the day blooming flowers and strongly scented and whitish in night blooming flowers.

Like sepals they may also be fused or free. Correspondingly, they are of two types : 

(a) Gamopetalous :- When all the petals are fused fully or partially e.g. Petunia.

(b) Polypetalous :- When the petals are free from each other e.g. Hibiscus. 

Functions

  • The primary function of corolla is to attract insects and other animals for pollination.
  • The corolla encloses and protects the stamens and pistil.
  • Some petals are scented with a nectary at the base which produces sugary nectar.

Perianth

In some flowers, such as Asparagus, non-essential parts of the flower are not differentiated into sepals and petals. They are, collectively known as perianth. The individual perianth lobes are called tepals. The tepals may be greenish (seploid) or beautifully coloured (petaloid).
The corolla or perianth may sometimes bear outgrowths, such as spurs, nectaries and corona.

Spur

It is the beak-like tube shaped outgrowth of perianth which contains nectar e.g Balsam, Nasturtium, Larkspur, etc.

Nectary

Special glands developed on or at the base of floral structures are known as nectaries which secrete nectar.

Corona

Sometimes, when the corolla is split, an additional whorl consisting of lobes, scales or hair is formed. It adds to the beauty of the flower.

Androecium

Inner to and above the petals are present male reproductive organs called stamens. They collectively constitute the androecium. The stamens are present either in a single or more whorls.

Each stamen may be regarded as a highly modified leaf (called microsporophyll). A typical stamen is differentiated into two parts i.e.

(a) filament
(b) anther.

The filament is a long stalk. It supports a fertile head called anther. The two anther lobes are attached at the back by a small connective. Each anther consists of two lobes.

Each lobe is differentiated into two chambers called pollen sacs, filled with pollen grains. The wall of pollen grain is made-up of two layers, i.e.

(i) Exine - It is the outer, ornamented, protective, cutinized and rough layer. It often bears spiny outgrowths. 

(ii) Intine - It is the thin, delicate, cellulose layer that grows into the pollen tube. 

Filaments are attached in different manners with the anther and accordingly, they are classified as 

(a) Basifixed - filament attached to the base of the anther e.g. Mustard, Radish etc.

(b) Adnate - filament extending throughout the length of the anther in between the two lobes from base to apex or continuous with connective. e.g. Magnolia

(c) Dorsifixed - filament attached to the back of the anther. e.g. Prunus, Acacia.

(d) Versatile - filament attached to the back of the anther by a sharp point, leaving the anther free to swing in the air e.g. paddy, grasses etc.

The stamens exhibit great diversity with respect to the fusion, their attachment to different whorls and size. 
Accordingly, they are categorized into the following five types : 

  1. Polyandrous - All the stamens are free from each other. Their filaments may be of same or different sizes. e.g., Brassica.
  2. Monoadelphous - The filaments of all the stamens fuse into a staminal tube but, their anthers are free e.g. China rose, cotton etc.
  3. Diadelphous - The filaments of stamens fuse into two bundles but anthers are free e.g. pea, sesbania, etc.
  4. Polyadelphous - The filaments of stamens unite to form more than two bundles e.g. silk cotton, Citrus.
  5. Syngenesious - The filaments are free but anthers of all the stamens unite together forming a cylindrical tube around the style e.g. sunflower

Functions:
  • The anthers produce pollen grains which contain male gametes.
  • The filament attachment with anthers is such that, it helps in pollination.

Gynoecium

Located in the centre of the flower is the female reproductive organ called gynoecium or carpels. A flower is composed of one or more carpels.

The free occurring units of the carpels in a flower are called pistils. Each carpel is a flask shaped structure. 

It consists of three parts i.e. 
(a) stigma
(b) style
(c) ovary 

Stigma - It is the tip of the carpel which is slightly swollen and usually sticky. It is meant for receiving pollen grains and their germination.

Style - It isa long tubular stalk that connects stigma with ovary.

Ovary - It is the swollen, basal part of the carpel. The ovary may be divided into either a single chamber (unilocular) or many chambers (multilocular). Each chamber contains one or more rounded, egg - like structures called ovules which on maturity produce seeds. Each ovule encloses a large ovul structure called embryo sac.

Functions 

  1. The hollow cavity of ovary contains ovules.
  2. Each ovile contains an egg cell.
  3. The position and length of Style bearing stigma in such that is help in pollination.
  4. The stigma structurally adapted to receive or trap the pollen grains.

CHARACTERISTICS OF THE FLOWERS

The flowers possess following characteristics :
  1. The flower is a highly modified and specialized shoot, meant for sexual reproduction.
  2. The nodes and internodes are highly condensed to form a flat thalamus or receptacle.
  3. The thalamus can be flat, conical, concave or dome-shaped in different species.
  4. The thalamus is very short. It is usually borne at the end of a stalk called pedicel.
  5. The flower arises in the axil of a leaf or leaf- like structure called bract.
  6. The floral parts are borne on the thalamus in the form of four whorls.
  7. The four rings or whorls of floral structures from outer to inner side are, calyx (sepals), corolla (petal), androecium (stamens) and gynoecium (carpels).
  8. Any flower having all the four whorls is called complete. Whereas, those flowers in which any whorl is missing are called incomplete.
  9. Androecium and gynoecium are called essential parts as they directly help in sexual reproduction. Whereas, calyx and corolla are non-essential parts as they are not directly involved in the process of reproduction.