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Plant Biology - Flower

Flower:

A shoot is modified for sexual reproduction, and then it is called as flower. A typical flower contains four whorls (calyx, corolla, androecium and gynoecium) and thalamus.

1.  Calyx – Outermost whorl of the flower made up of sepals. Sepals are green and protect the other whorls of the flower.
2.  Corolla – Present inside the calyx and made up of petals. Petals are different in color and shapes and protects the other whorls present inside it. It attracts insects for pollination due to its color.
3.  Androecium – Present inside the corolla and made up of stamens. Each stamen contains filament, anther and a connective. Filament and anther are joined through connective. Pollen grains are produced within anther.
4.  Gynoecium – Present at the inner most side of the androecium and made up of carpel. Each carpel contains ovary and stigma. Ovules are produced within ovary.
5.  Thalamus - An expanded tip of the pedicel. Components of whorls are concentrically arranged on a thalamus.

Calyx and corolla do not participate in the process of reproduction but helps in protection and attraction and hence they are called as accessory floral whorls.

Androecium and gynoecium takes part in the process of reproduction and hence called as essential floral whorls.


Types of flower:

Flowers are classified based on the whorls present in it or on the position of the ovary present in gynoecium.

Based on the whorls:

1.  Complete flower – All four whorls are present in the flower
2.  Incomplete flower – Any one whorl is absent in the flower
3.  Bisexual flower – Both the essential floral whorls are present in the flower
4.  Unisexual – Any one essential floral whorl is absent in the flower
Male flower – androecium is present
Female flower – gynoecium is present

Based on the position of ovary:
1.  Hypogynous – Ovary occupies more space as thalamus is conical in shape e. g. Datura
2.  Perigynous – Ovary is present in the centre and other floral whorls are arranged on the rim of the thalamus as thalamus is flat and disc like e.g. Rose
3.  Epigynous – Ovary is inferior and other whorls are arranged above the ovary as thalamus envelops the ovary e.g. sunflower, cucumber

Based on the shape of flower:
1.  Regular flower – Flower is divided into two equal halves along any longitudinal plane e.g. Mustard
2.  Irregular flower – Flower is divided into one plane only e. g. Bean


Aestivation:

The arrangement of different whorls in the bud is called aestivation. Aestivation is of different types – Valvate, twisted or imbricate

Placentation:

The part of ovary where ovule develops is called placenta and the arrangement of ovules within an ovary is called palcentation. It may be marginal, axile or basal.

Inflorescence:

The arrangement of flowers on the rachis of plant is called Inflorescence. A part of the plant which bears flowers is called rachis or peduncle.

Inflorescence is of two types:


1.  Racemose Inflorescence: Apical bud produces new flowers in an acropetal fashion on the rachis.
a)  Raceme – Flowers stalked e.g. Mustard
b)  Spike – Flowers are sessile e.g. Adhatoda
c)  Catkin – Spike axis is weak and suspended e.g. Mulberry
d)  Umbel – Flowers are arranged on the condensed rachis like the spokes in the umbrella e. g. Onion
e)  Capitulum – Flat and disc like rachis e. g. Sunflower

2.  Cymose inflorescence: Apical bud is modified into flower
a)  Solitary cymose – Only one flower develos at the tip of rachis e.g. Hibiscus
b)  Monochasial cyme – The apical bud gives a single branch before turning into flower e. g. Hamelia
c)  Bilateral monochasial cyme – New branches are developed on the opposite sides of the axis e. g. Heliotropium
d)  Dichasial cyme – Apical bud gives two lateral branches before turning into flower e.g. Jasmine
e)  Multiparous cyme – Many branches develops from the apical bud e. g. Red oleander



Self study:

Q-1: Match the following

A B
Placentation Modified shot for sexual reproduction
Aestivation Arrangement of flowers on the rachis
Inflorescence Arrangement of ovules within an ovary
Flower Arrangement of various whorls in the bud

Answer:

A B
Placentation Arrangement of ovules within an ovary
Aestivation Arrangement of various whorls in the bud
Inflorescence Arrangement of flowers on the rachis
Flower Modified shot for sexual reproduction

Q-2: Calyx of the flower contains …………..
  1. Petals
  2. Ovary
  3. Sepals
  4. None

Answer: Calyx of the flower contains sepals which are green in color and look like leaf.

Q-3: Pollen grains are produced within ………..of stamen.

  1. Anther
  2. Filament
  3. Connenctive
  4. Ovary

Answer: Pollen grains are produced within anther of the stamen and helps in reproduction.
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