Development of the Seed and Formation of the Fruit

After fertilisation, the ovule develops into a seed, and the ovary matures into a fruit. These processes mark the beginning of the plant’s reproductive success — ensuring protection and dispersal of the next generation. Let’s break down how seeds and fruits develop step-by-step after fertilisation.

1.0Development of the Seed

The seed is the fertilised ovule. It consists of three main parts: the seed coat, the embryo, and the endosperm.

1. Endosperm Development

The endosperm provides nourishment to the developing embryo. It forms from the primary endosperm nucleus (PEN), and its development precedes that of the embryo. There are two main types of endosperm development:

• Free-nuclear endosperm: The PEN undergoes repeated mitotic divisions without cell wall formation, leading to a multinucleated cytoplasm. This is common in coconut water.
• Cellular endosperm: The PEN's divisions are immediately followed by cell wall formation, resulting in a cellular tissue. Coconut meat is an example of cellular endosperm.

In some seeds, like castor bean and maize, the endosperm persists and is used by the germinating seedling. These are called endospermic or albuminous seeds. In others, like beans, peas, and groundnuts, the embryo consumes the endosperm completely during development, so the mature seed lacks it. These are called non-endospermic or exalbuminous seeds.

2. Embryo Development

The zygote begins its development only after a certain amount of endosperm has formed to ensure a nutrient supply. The zygote divides to form a proembryo, which then differentiates into the mature embryo.

The mature embryo has a main axis and one or two cotyledons.

• Monocots (monocotyledonous plants): The embryo has a single cotyledon, such as in maize.
• Dicots (dicotyledonous plants): The embryo has two cotyledons, such as in beans.

The part of the embryonic axis above the cotyledons is the epicotyl, which terminates with the plumule (future shoot). The part below the cotyledons is the hypocotyl, which terminates with the radicle (future root).

3. Seed Maturation and Dormancy

As the seed matures, its water content reduces significantly, making it relatively dry. This is a crucial step for seed dormancy, a state of suspended growth that protects the embryo and ensures germination only under favorable conditions. The seed coat, formed from the integuments of the ovule, also becomes hard and protective.

2.0Formation of Fruit

1. Development from the Ovary

• The ovary of the flower enlarges after fertilization and transforms into the fruit.
• The ovarian wall differentiates into three layers known collectively as the pericarp:
• • Epicarp (outer layer) – forms the skin of the fruit
  • Mesocarp (middle layer) – often fleshy and edible
  • Endocarp (inner layer) – may be hard or thin depending on fruit type

2. Parthenocarpic Fruits

• Sometimes fruits develop without fertilization; these are called parthenocarpic fruits (e.g., banana, seedless grapes).
• Such fruits do not contain seeds and are often induced by plant hormones like auxins or gibberellins.

3. Types of Fruits

• True Fruits: Develop only from the ovary (e.g., mango, tomato).
• False Fruits (Accessory Fruits): Develop from parts other than the ovary (e.g., apple, strawberry – where thalamus contributes).

4. Function of the Fruit

• Fruits protect seeds during development and help in seed dispersal.
• They act as storage organs, providing nutrients and sugars for humans and animals.