Parts of a Flower and their Functions -digieduco

Definition : A flower is a modified reproductive shoot-tip of determinate growth, bearing either only microsporophylls (stamens) or megasporophylls (carpels) or both, and may or may not be associated with accessory leaves, meant for the production of fruit and seeds.

Flower section

Parts of a Typical Flower : A flower consists of an axis known as thalamus, on which four different sets or whorls of floral members are inserted viz.

(a) Outermost, i.e., flrst accessory whorl‘ of sepals = Calyx square..
(b) Above the calyx, the second accessory whorl of petals = Corolla square
(c) Above the corolla, first essential whorl of stamens = Androecium.
(d) Next above, second essential whorl of carpels = Gynoecium or Pistil.

THALAMUS-The thalamus or axis or torus is the direct prolongation of the pedicel and bears four whorls of floral members. Thalamus is also known as receptacle which is often short and suppressed, usually convex or concave. Sometimes it is long, showing distinct internodes or it may be dilated into flat or concave structure. Sometimes thalamus presents certain modifications of forms as various outgrowths which are seen between floral whorls ; such modification of the thalamus is known as disc. In case of Artabotrys somewhat elongated and conical thalamus noted bearing spirally arranged floral leaves.

CALYX-It forms the outermost envelope of the floral whorl and is the first accessory members, its respective leaves are called sepals which may remain free or united--the former is known as polysepalous calyx, the latter as gamosepalous calyx. Sepals are mostly green and are always sessile. The number of sepals in a calyx whorl may vary from one to many.

COROLLA-It is the second accessory member of the floral whorl. Its constituent leaves are known as petals, which are delicate and coloured or white, rarely greenish. Petal may be free or united forming polypetalous or gamopetalous corolla respectively. The petal may be sometimes stalked, the stalk of petal is called claw ; the expanded portion of the petal is called limb. The number of petals in a corolla varies from one to many. Above mentioned two whorls (calyx and corolla) are termed accessory whorls.

ANDROECIUM-The third member and the first essential whorl is the androecium ; its individual members are known as stamens. In an androecium, the number of stamens may be one to many. The stamens may remain free or variously united or attached to other whorls. A stamen has a slender stalk called filament, which bears at its tip anther lobes (microsporangia) containing pollen grains i.e. microspores. The filament may be short, slender or flat, or in some cases absent-then the stamen is called sessile.

GYNOECIUM OR PISTIL-It is the topmost or centrally placed floral member and forms the second essential whorl ; its individual members are known as camels. In a gynoecium the number of carpel varies from one to many. The gynoecium consists of a swollen basal structure-the ovary, the long filiform structure called style and the knobed tip of the style called stigma. The carpels may remain free or united, the former is known as apocarpous gynoecium, the latter as syncarpous gynoecium.

Functions of Floral Members :

CALYX-(1) Its function is mainly protection ; (2) When coloured, it acts as flag apparatus for insect pollination ; green calyx is photosynthetic in function.

COROLLA-(1) The function of corolla is to attract insects i.e. the function of flag apparatus. (2) In some cases the bases of petals act as secreting of nectar owing to the presence of glands. (3) Secondary function of corolla is protection of the essential members.

ANDROECIUM-The function of which is the production of microspores i.e. pollen grains within anther lobes.

GYNOECIUM-The function of which is the production of (a) megaspore, (b) fruits and finally (c) seed or seeds.