FRUITS

FRUITS

Definition of Fruits

A fruit is the matured ovary of a flower, usually containing one or more seeds. It develops after fertilization of the ovule and serves to protect the seeds and help in their dispersal. In some plants, fruits can also form without fertilization; such fruits are called parthenocarpic fruits (e.g. banana, pineapple). 

Structure of a Fruit
 A typical fruit consists of two main parts:

1. The Pericarp – This is the wall of the fruit that develops from the ovary wall. It is usually  divided into three layers:

• Epicarp: The outer skin or covering of the fruit.
• Mesocarp: The fleshy, edible middle layer.
• Endocarp: The inner layer that encloses the seed(s).

2. The Seed(s) – Found within the fruit, developed from the ovule.

Examples:
 In mango – Epicarp (outer skin), Mesocarp (fleshy part), Endocarp (hard stone around the seed).
 In orange – Epicarp (peel), Mesocarp (white fibrous part), Endocarp (juicy sacs).

A fruit normally consists of the following parts:
 - a fruit wall or pericarp
- the seed or seeds inside the fruit.
- the remains of the style or scar showing the point of attachment of the style.
- the fruit stalk or scar showing the point of attachment of the fruit to the plant. 

Differences Between a Fruit and a Seed

• Fruit develops from the ovary of a flower, while a seed develops from the ovule inside the ovary.
• The fruit protects and aids in the dispersal of seeds, while the seed germinates to produce a new plant.
• A fruit has pericarp (epicarp, mesocarp, endocarp), while a seed has a seed coat, embryo, and cotyledons.
• Fruits form after fertilization of the ovary, while seeds form after fertilization of the ovule.
• Examples of fruits include mango, orange, and tomato, while examples of seeds include bean seed, maize grain, and groundnut seed.

Classification of Fruits
Fruits can be classified based on their origin and structure.

A. Based on Origin

1. True Fruits – It is developed from the ovary only. It consists of a pericarp and a seed. Examples: mango, orange, tomato.
2. False Fruits (Accessory Fruits) – Developed from other floral parts such as the receptacle along with the ovary. Examples: apple, pear, strawberry.

B. Based on Structure

1. Simple Fruits – This type of fruit is developed from a single ovary of one flower. The ovary may be monocarpous (e.g. cowpea) and syncarpous (e.g. tomato)
2. Aggregate Fruits – Develop from several ovaries of one flower. Examples: strawberry, raspberry.
3. Composite (Multiple) Fruits – Develop from ovaries of many flowers that fuse together. Examples: pineapple, fig.

C. Based on Nature of their Pericarps

• Fleshy fruits: the whole pericarp or at least one of its layers is thick, soft and fleshy especially when it is ripe. E.g. tomato, mango, orange.

Types of Fleshy Fruits

(i) Drupe:  A drupe is a fleshy fruit with a single seed enclosed in a hard, stony endocarp (the “stone” or “pit”). The fruit has three parts: the epicarp (outer skin), mesocarp (fleshy part), and endocarp (hard layer surrounding the seed). The epicarp is thin, the mesocarp may be fibrous while the endocarp is hard. Examples include mango, coconut, peach, and cherry.

(ii) Berry: A berry is a fleshy fruit in which the entire pericarp (epicarp, mesocarp, and endocarp) is soft and edible. It usually contains many seeds. Examples include tomato, banana, grape, guava, and pawpaw.

(iii) Pome: A pome is a simple false fruit that develops from both the receptacle and the ovary of a flower. The fleshy edible part comes from the receptacle, while the core that contains the seeds comes from the ovary. Examples include apple, pear, and loquat.

(iv) Sorosis: A sorosis is a multiple or composite false fruit formed from the ovaries of many flowers in an inflorescence that fuse together to form one large fruit. Examples include pineapple, mulberry, and jackfruit.

• Dry fruits: This is the type of fruit in which the pericarp becomes dry, hard and woody or fibrous when the fruit ripens. E.g. groundnut, bean, maize. They are mainly divided into two groups — dry dehiscent fruits and dry indehiscent fruits.

Dry Dehiscent Fruits
 Dry dehiscent fruits are those that split open naturally when they mature in order to release their seeds. The splitting is an adaptation that helps in seed dispersal by wind, water, or other agents. The wall of the fruit (pericarp) usually dries up and cracks along definite lines of weakness.

Types and Examples:

1. Legume (Pod):
 This fruit develops from a single carpel and splits along two lines (the dorsal and ventral sutures) when dry. Each half curls outward, allowing the seeds to scatter. Examples: Bean, pea, groundnut, flamboyant.

2. Capsule:
 This fruit develops from two or more carpels and splits in various ways — from the top, sides, or through pores — to release the seeds. Examples: Cotton, hibiscus, castor, okra.

3. Follicle:
 This is a fruit formed from a single carpel that splits open along one side only when mature. Examples: Periwinkle, columbine.

4. Siliqua:
 This fruit is formed from two fused carpels that split along both sides but leave a thin partition (replum) in the middle where the seeds are attached. Examples: Mustard, cabbage.

Dry Indehiscent Fruits
Dry indehiscent fruits are those that do not split open when mature. The seeds remain enclosed within the fruit wall (pericarp) and are released only when the fruit decays or is eaten by animals. This type of fruit is often adapted for dispersal by animals, wind, or water.

Types and Examples:

1. Caryopsis:
 The seed coat is completely fused with the pericarp, making the seed and fruit wall inseparable. The entire grain acts as a single seed. Examples: Maize, rice, millet, wheat.

2. Achene:
 The seed is free within the pericarp but not fused to it. It can be separated easily from the fruit wall. Examples: Sunflower, buttercup.

3. Nut:
 This is a one-seeded fruit with a hard, woody fruit wall that does not open. It usually has a tough shell protecting the seed. Examples: Groundnut, walnut, cashew nut, chestnut.

4. Cypsela:
 This type of fruit develops from an inferior ovary and often has a feathery or hairy structure (pappus) that helps it float in the air for wind dispersal. Example: Tridax, dandelion.

5. Samara:
 A samara is a dry, indehiscent fruit with wing-like outgrowths of the pericarp that enable it to be carried by the wind. Examples: Maple, elm.

Dispersal of Seeds and Fruits

Dispersal of seeds and fruits is the scattering or spreading of mature seeds or fruits away from the parent plant. It occurs after the fruit matures, ensuring that new plants do not grow too close to their parent. The process is essential for the survival and distribution of plant species in different environments.

Importance of Dispersal of Seeds and Fruits

1. Reduces Overcrowding: It prevents young plants from growing too close to the parent plant, thereby reducing competition for light, water, and nutrients.
2. Prevents Competition: Helps minimize competition among seedlings and between seedlings and the parent plant.
3. Colonization of New Areas: Allows plants to spread and grow in new places where conditions may be more favorable.
4. Ensures Survival of the Species: If one area becomes unfavorable, seeds dispersed to other areas can continue the species.
5. Promotes Variation: Dispersal can lead to cross-pollination between plants in different areas, encouraging genetic diversity.
6. Reduces Risk of Disease: Dispersed seeds are less likely to be affected by the same pests or diseases that affect the parent plant.
   
    

Agents of Dispersal of Seeds and Fruits

The agents of dispersal are the forces or means by which seeds and fruits are carried from one place to another. These include wind, water, animals, explosion, and man.

 

1. Dispersal by Wind (Anemochory)
 Some fruits and seeds are very light or have special structures like wings or hairs that enable them to be carried by the wind.
 Adaptations:

• Small, light, and dry seeds.
• Wing-like extensions or feathery hairs.
   Examples:
   Tridax, cotton, dandelion, African tulip tree, and maple.
  
   

2. Dispersal by Water (Hydrochory)
 Fruits or seeds dispersed by water are light and can float for long distances without being damaged. They often have fibrous or spongy coverings that trap air and help them stay afloat.
 Adaptations:

• Light and waterproof fruit walls.
• Fibrous or spongy tissues for buoyancy.
   Examples:
   Coconut, water lily, water lettuce.
  
   

3. Dispersal by Animals (Zoochory)
 Animals disperse seeds and fruits in several ways:

• Fleshy fruits are eaten by animals; the seeds pass out undigested in their droppings.
• Hooked or sticky fruits attach to the fur or feathers of animals and are carried to new places.
   Adaptations:
• Bright colors and sweet taste to attract animals.
• Hard seed coats to resist digestion.
• Hooks, spines, or sticky hairs for attachment.
   Examples:
   Mango, orange, tomato (eaten by animals); burdock, spear grass, tridax (attach to fur).
  
   

4. Dispersal by Explosion (Autochory)
 Some fruits split open suddenly when they are ripe, throwing their seeds away from the parent plant. The force of the bursting helps the seeds scatter over a short distance.
 Adaptations:

• Dry fruit walls that split when tension builds up.
   Examples:
   Balsam, castor oil plant, pea, and flamboyant.
  
   

5. Dispersal by Man (Anthropochory)
 Humans play an important role in dispersing seeds intentionally (by planting) or unintentionally (when seeds cling to clothing or are transported with goods).
 Examples:
 Maize, groundnut, yam, and other cultivated crops.