Plant Anatomy: Flower Structure

Structure of a Flower

• A flower consists of four floral whorls: calyx, corolla, androecium, and gynaecium, arranged in sequence from outside to inside.
• Androecium and gynaecium are called 'essential whorls' because they perform the function of reproduction.
• Calyx and corolla are called 'accessory whorls' because they are responsible for protecting the inner whorls.

Components of a Flower

• Members of calyx are called 'sepals' and are green in color.
• Members of corolla are called 'petals' and are variously colored.
• Androecium is the male whorl and its members are called 'stamens'.
• Gynaecium is the female whorl and its members are called 'carpels'.

Types of Flowers

• A flower is called 'bisexual' if both androecium and gynaecium are present in the same flower.
• A flower is called 'unisexual' if only one of the essential whorls is present in the flower.
• A unisexual flower with only androecium is called a 'male flower', and a unisexual flower with only gynaecium is called a 'female flower'.

Support and Attachment

• Many flowers have a stalk for support, called a 'pedicel', and are called 'pedicellate'.
• Flowers without a stalk are called 'sessile'.

Reproductive Process

• Ovary is present at the basal end of each carpel, and contains one or many ovules.
• Each ovule contains an embryo sac formed by meiosis, consisting of a haploid egg cell and two haploid polar nuclei.
• Pollination occurs when pollen grains from an anther are transferred to the stigma, either through abiotic or biotic agents.
• Pollen germinates on the sticky stigma, forming a pollen tube that carries male gametes to the embryo sac.
• Fertilization occurs when a male gamete unites with the egg cell to form a zygote.
• Double fertilization occurs when the second male gamete unites with the two polar nuclei to form endosperm.