Parts of a Flower
Flowers are vital as they are the seat of sexual reproduction. They produce fruits and seeds. A flower is a modified shoot because it has nodes very close to one another and floral leaves arranged in successive whorls.
The flower is borne on a stalk called pedicel. The pedicel has a swollen tip known as thalamus or receptacle on which are borne four whorls successively in definite order.
Accessory Whorls
1. Calyx (collection of sepals) - The outer most whorl of green sepals whose main function is protection.
2. Corolla (collection of petals) - The next whorl of variously coloured petals. They help in attracting insects for pollination.
Reproductive Whorls
3. Androecium (male reproductive part) consists of collection of stamens. Each stamen has a long slender filament with a bilobed anther at it’s tip with a connective. Anthers produce pollen grains for pollination.
4. Gynoecium (female reproductive part) - centrally located. It consists of a collection of one or more carpels which organize to form one or more pistils. Each pistil has three parts:
- Ovary - It is the swollen basal part, one to many chambered (called locules) containing ovules which get fertilized to form seeds and the, fertilized ovary forms the fruit.
- Style - It is the elongated tube connecting the upper part of ovary to stigma.
- Stigma - It is the receptive surface for pollen.
Variations in Sepals and Petals
(i) Polysepalous and Polypetalous - sepals or petals are free respectively.
(ii) Gamosepalous and Gamopetalous - all sepals or petals are fused, respectively.
(iii) Perianth - Sepals and petals are not distinguishable. Example: onion
Variations in Stamens
The stamens show variation in their cohesion (fusion).
(i) Monadelphous - filaments fused into one bundle but anthers are free. Example: china rose
(ii) Diadelphous - filaments fused to form two bundles. Example: pea
(iii) Polyadelphous - filaments fused to form many bundles. Example: lemon
(iv) Syngenecious - filaments are free but anthers are fused. Example: sunflower
(v) Synandrous - stamens are fused throughout the length. Example: cocks-comb.
(vi) Epipetalous - stamens are attached to petals by their filaments but anthers are free. Example: brinjal
(vii) Didynamous - four stamens, two short and two long. Example: tulsi
(viii) Tetradynamous - six stamens, inner four are long and outer two are short. Example: mustard
Variation in Carpel
On the basis of number of carpels in a pistil, flowers may be
(i) Monocarpellary - If in a Gynoecium pistil has only one carpel Example: pea
(ii) Polycarpellary - If the Gynoecium has many carpels (Example: china rose). It may be
- (a) syncarpous - two or more carpels are fused to form a pistil. Example: tomato, mustard
- (b) apocarpous - carpels are free. Example: Ranunculus, lotus