Major Parts of a Flower

The Structure and Function of a Flower

• A flower is a reproductive structure of angiosperms, the most diverse and complex plant species in the world.
• The primary function of a flower is to produce seeds or seed-bearing fruits.
• The main components of a flower, called whorls, are in four distinct parts: sepals, petals, androecium, and gynoecium.

The Ovary of a Flower

• The ovary is a part of a plant that functions as the structure where fertilization and seed development occur.
• The ovary is usually located at the base of the flower, below the stigma and style.
• One or more eggs, or ovules, are housed in the ovary.
• The arrangement of ovules varies among flower species.

Ovary Positions

• There are three types of ovary positions: hypogynous, perigynous, and epigynous.
• Hypogynous: the ovary sits above the attachment of the petals, stamen, and sepals (e.g., tulip, hibiscus).
• Perigynous: the petals, stamen, and sepals are attached at a mid-point (e.g., rose, peach).
• Epigynous: the ovary sits below the petals, stamen, and sepals (e.g., daffodil, squash).

Structure and Function of the Ovary

• The ovary is composed of a number of structures to ensure ovule development and the production of seed-bearing fruit.
• The ovary wall eventually develops into the pericarp in fruits (outer, protective covering).
• The locule is the compartment that houses the ovule.
• The ovule is connected to the placenta by the funiculus.

Placentation

• The arrangement of ovules in a flower is termed placentation.
• There are five types of placentation: parietal, free central, axile, basal, and marginal.
• Examples of each type of placentation include:
  • Parietal: cucumber
  • Free central: primrose
  • Axile: lemon
  • Basal: marigold
  • Marginal: pea

Function of the Ovary

• The function of the ovary is to prepare the ovules for fertilization, protect developing zygotes, and develop into a seed-bearing fruit.
• The walls of the ovary grow and thicken after fertilization occurs and as seeds continue to develop.

Fruit Development

• The purpose of fruit development is an adaptation of angiosperms as a way to disperse seeds for the continuity of the species.
• Ripened fruit may develop from the ovary or other parts of the flower, such as the perianth.
• Examples of fruits include peppers, squash, nuts, wheat, and corn.

Ovule Functions

• The ovules of angiosperms function to produce a seed that remains dormant until germination outside the fruit.
• Unique to angiosperms, the ovule of a flower undergoes double fertilization.

Double Fertilization

• The process of double fertilization begins with pollen formation and embryo sac formation.
• The double fertilization steps include:
  • Pollen attaches to the stigma, and a pollen tube descends into the ovary.
  • Two sperm cells are formed and enter the embryo sac.
  • One sperm cell fertilizes the egg, while the other fertilizes the two polar nuclei.
  • The resulting zygote begins to divide, and the endosperm develops to provide nutrients for the zygote.

Petal Functions

• The beautiful petals of a flower serve to protect the style and stigma, but even more importantly, petals serve to help the pollination process.
• Petals attract pollinators in several ways, including:
  • Perfume emanating from petals
  • Color and patterns (called nectar guides)
  • Ultraviolet light, which is visible to bees and provides a map toward the center of the flower.