Structure of Flower

 STRUCTURE OF FLOWER

 

✿ FLORAL WHORLS

                    There are main two types of Floral whorls

1. Accessory Floral Whorls
2. Essential Floral Whorls

Accessory Floral Whorls :-

            There are two types of Accessory Floral Whorls

• Calyx = In calyx there are sepals.
• Corolla = In corolla there are petals.

Essential Floral Whorls :-

            There are two types of Essential Floral Whorls.

• Androecium =In androecium there are many stamens which consist three parts namely, anther, filament and connective
• Gynoecium = In gynoecium there are one carpel/pistil which consist three parts namely, stigma, style and ovary.

CALYX

Sepals

                    The sepals are small modified leaves located around the base of a flower. Sepals support the flower and protect the other flower parts while the flower is closed before and after pollination. You can find sepals still attached to some fruits.

The green sepals of a sunflower. 

COROLLA

Petals

                    The petals are modified leaves that help attract pollinators to the flower. Petals are often large and brightly colored and may have patterns of colors in the ultraviolet spectrum which can be seen by insects even though it is invisible to the human eye. Interestingly, petals’ bright colors and patterns have evolved to send a signal to pollinators: “This way to the food!”

The brightly colored petals of a rose.

ANDROECIUM

                    The male reproductive whorl of flower is called as androecium. Individual members of androecium is called as stamen. Stamen consist of filament, connective and anther.

Stamen

Structure of Anther :-

• Anther is generally dithecous (2 lobed) and tetrasporongiate (4 pollen sacs).
• Each monothecious anther consist two pollen sacs.
• An immature stage of anther is represented by group of parnchymatus tissue surrounded by single layered epidermis.
• The heterogenesity (differentiation) arises when some hypodermal cells get transformed into archesporial cells.
• The archesporial cells divides into an inner sporogenous cell and outer primary parietal cell.
• Sporogenous cells forms microspore mother cell.
• Parietal cell undergoes divisions to forms anther wall layers.

4 Layered Anther Wall

1. Outer protective epidermis made of tabular (flattened) cells.
2. Sub-epidermal emdothecium with radially elongated cells.
3. 1-2 middle layers
4. Innermost nutritive layer is tapetum that encloses sporongenous tissue (microspore mother cell).

GYNOECIUM

Female reproductive whorl of flower is gynoecium. Individual members of gynoecium is called as carpel (megasporophyll). Typical carpel has three parts via, ovary, style and stigma.

Carpel

❉ Types of Carpels :-

➪  Apocarpous carpels are free.
      Ex :- Michelia.

➪  Syncarpous carpels are fused.
      Ex :- Brinjal.

❉ Types of Ovary :-

➪  Uniovulate only one ovule is present in a ovary.
      Ex :- Mango

➪  Multiovulate multiple ovules present in a ovary.
      Ex :- Chikoo (Sapota)

Structure of Anatropus Ovule

• In most of the angiosperms anatropus ovule is present.
• Ovule is attached to the placenta with the help of funiculus.
• The point of attachment of funiculus to placenta is called as Hilum.
• Embryo sac is developed from one of the nucellar cell.
• Embryo sac is protected by double layered integument i.e inner integument and outer integument.
• The opening of integument toward egg apparatus is called as Micropyle.
• The end opposite to micropyle is called chalazal end.

✦ Development of Embryo Sac :-

• One of the nucellar cell acts as megaspore mother cell (2n).
• MMC(2n) undergo meiosis to form megaspore tetrad of haploid cell.
• From megaspore tetrad three cells toward chalazal end gets degenerated.
• Megaspore at micropyle end is called functional megaspore as it develop into embryo sac.
• Functional megaspore is nourished and increases in size.
• Functional megaspore (grown megaspore) undergo three repetative mitotic division to form 8 nucleated condition.
• 1 nuclei form each pole i.e polar nuclei reaches to the centre and get fused to form secondary nucleus.
• Later on cell wall is formed around each nucleus except secondary nucleus.
• 8 nucleated 7 celled embryo sac is formed.
• Three cells towards chalazal end in embryo sac are called antipodals.
• Three cells towards micropyle end forms egg apparatus.
• In egg apparatus two lateral cells are called synergids and middle one is egg cell.
• Synergid provide nourishment to egg cell and also direct pollen tube into embryo sac.
• As embryo sac is developed from one megaspore, it is called monosporic development.
• As embryo sac is developed within megaspore, it is also called endosporic development.
• Development of embryo sac is monosporic and endosporic.