What is flower?
The angiospermic flower is a modified, condensed, reproductive shoot of determinate growth, meant for the production of fruits and seeds. So, the flowers represent the reproductive structure of higher plant, which is the most important organ of higher plants. They are only produced after the plants have attained maturity and help in the perpetuation of a particular variety of plant. It undergoes sexual reproduction to produce the fruit and seed. The seeds germinate to produce a new plant again.
Now we shall go for a discussion about different flower parts. The typical flower has the different flower parts having specific functions. The flower may be sessile or may have a stalk called pedicel. It may be subtended by a bracteole below. The tip of the pedicel is a flattened structure called thalamus or receptacle, on which the flower parts are arranged. A typical flower consists of thalamus and four different floral parts inserted in the receptacle. They are described below:
Torus or Thalamus
Structure :
i) The terminal part of a short or suppressed branch is called thalamus.
ii) It gives rise to the four different flower parts, i.e., calyx, corolla, androecium and gynoecium.
iii) It consists of four different nodes, corresponding to the four different flower parts, and three condensed internodes remaining in between them.
iv) It may have variable shapes, i.e., flat, concave, convex or conical in nature.
Functions :
i) It represents the area of attachment between the flower and the pedicel.
ii) It supports the floral parts.
The Accessory whorls:
They are so called because they do not take part in sexual reproduction. They include thecalyx and corolla.
Flower Parts
Calyx
Structure
i) It is the outermost and lowermost of flower parts.
ii) The individual units of calyx are called sepals.
iii) Each of the sepals is green, leaf-like sessile structures.
iv) It may be subtended by epicalyx, as in chinarose.
v) The number of sepals may be three, four or five.
vi) The sepals may be united in gamosepalous and free in polysepalous condition.
Functions :
i) These flower parts protect the inner whorls.
ii) They prevent loss of water by evaporation.
iii) They help in the preparation of food by photosynthesis, as they contain chlorophyll.
Corolla
Structure :
i) The second accessory whorl, situated next to calyx.
ii) The individual units of corolla are called petals.
iii) Each petal is colored, delicate, leafy structure.
iv) Sometimes the petals are undifferentiated from the sepals, and they are called perianth.
v) They petals usually are differentiated into upper expanded portion and lower stalk-like portion.
vi) If the differentiation is highly distinct, they form the upper limb and lower claw.
vii) Petals may also be free (polypetalous), or united (gamopetalous) in nature.
viii) The petals are mostly three, four or five in number, sometimes they are in multiples.
Functions :
i) These flower parts protect the inner essential whorls.
ii) They are bright colored and attract insect for pollination.
iii) They may prevent cross pollination and help in self pollination, as in cleistogamous flowers of Commelina.
The Essential or Reproductive whorls
They are the flower parts so called because they are directly involved in sexual reproduction. They are of two types, viz., androecium and gynoecium.
Androecium
Structure :
i) These flower parts are third inner whorl from outside and the first essential whorl is androecium.
ii) They represent the male reproductive structure.
iii) The individual units of androecium are called stamen or microsporophyll.
iv) Each stamen consists of basal stalk-like portion called filament and an apical sac-like portion containing the pollen grains called anther.
v) Each anther consists of two anther lobes, connected to the filament by connectives.
vi) The anther lobe consists of two microsporangia or spore-sac.
vii) The spore-sac consists of numerous microspores or pollen grains, which serve the purpose of male reproductive units.
viii) The pollen grains produce the male gametes.
Function :
[i] Production of pollen grains containing the male gametes.
Gynoecium
Structure :
i) These flower parts are the innermost whorl and the second essential whorl.
ii) The individual member of the gynoecium is carpel or pistil or megasporophyll.
iii) A carpel is divided into three parts, a swollen basal part called ovary, a median elongated part or the style and the terminal, flat pollen receptive part or stigma.
iv) The ovary may consist of one or more chambers or locules.
v) Each chamber may consist of one or many megaporangia or ovules of these flower parts.
vi) The ovule is attached to the wall of the ovary with a specialized tissue called placenta.
vii) The arrangement of the ovules in the ovarian locule is called placentation.
viii) The carpels may be united, i.e., syncarpous or they may be free, i.e., apocarpous in nature.
Functions :
i) Production of female gametes or megaspores is the main function of these flower parts.
ii) The ovary forms the fruit after fertilization.
iii) The ovules form the seeds after fertilization.