Introduction
Fruit is the pulpy or dry ripened ovary part of a flowering plant, enclosed by the seed or seeds. Apricots, bananas, and grapes, as well as corn grains, bean pods, tomatoes, cucumbers, and acorns and almonds are the examples of fruits. The cultivation of fruits and its treatment is by fruit farming. Processing of fruits and treatment of the nutrient composition is by fruit processing. Many animals are attracted by fruits that are pulpy and contain sugar amounts and these animals then disperse the seeds of fruits to new locations. Non-fleshy fruits use different mechanisms for seed dispersal. There are some plants in which fruits can develop without fertilization. This process is called parthenocarpy, and those fruits are seedless. The wall thickens and becomes differentiated into three, more or less distinct, layers during the development of the ovary.
Importance of Fruits
An apple a day keeps the doctor away! You must have heard this classic saying and understood the importance of fruits in keeping ourselves healthy and keeping the doctors at bay. Fruits are wholesome food. They are rich in vitamins and other nutrients. It is almost impossible to even think of any doctor who does not recommend fruits for good health and diet. Fruits do not just have health benefits, but they also have a taste. They taste delicious. But have you ever wondered how they are formed, what are their different parts, and how many types of fruits are there?
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How are Fruits Formed?
The first condition for the fruits to grow is the blooming of flowers. It is the flowers that bear the reproductive parts for the formation of fruits. Generally, it is the same flower that has both male and female units, but you can also find situations where flowers grow as having male or female reproductive parts on separate plants. In flower, the stamen is the male part which consists of the pollen sac called anther, and the pistil is the female part which consists of a stigma, style, and ovary. For the fertilization (reproduction process in flowers) to occur, the pollen must be transferred from the anther to the stigma. This process is called pollination.
If pollination does not occur, the pollen or male sperm will not be able to unite with the ovule, that is, the female egg in the ovary. Once the pollen has traveled down to the base of the pistil where the ovule resides, the nucleus of the male sperm unites or fertilizes with the ovule combining the female and male genetic material that goes on to form an embryo.
As the embryo crosses its two-cell stage, it is called a zygote, which later develops into a seed. As the zygote grows, the structure of the flower begins to change- the ovary starts to change into the fruit. The outside part of the ovary and the pistil becomes the skin of the fruit, or in some cases, the material outside the ovary wall becomes the fleshy and edible part of the fruit and parts like petals and sepals become the outer covering.
The fruit will survive only if the plant will. If the plant does not bear flowers, there will be no fruit formation.
What are the Different Parts of a Fruit?
To have an easier understanding of the structure or the parts of fruit, it is divided into two parts- first, the pericarp, and second, the seed.
The pericarp is that region of a fruit that is located outside the seed. It comprises the skin and flesh part of a fruit. It is, in turn, divided into three layers endocarp (the innermost layer around the seed), Mesocarp (middle layer), Epicarp (outermost layer).
Epicarp layer: It is also called the exocarp. It is the outermost layer of the fruit and the pericarp, which makes the fruit covering or the skin. In citrus fruits, the epicarp layer (the tough, thick skin) is called flavedo.
Mesocarp layer: It is the middle layer between the exocarp and the endocarp of the pericarp. It usually consists of the fleshy part of the edible part of the fruit like in apples and peaches. In citrus fruits like lemons, the white-colored portion just after the flavedo is the mesocarp layer, and it is called albedo. It is not the main edible part but is still eaten.
Endocarp is the innermost layer of the pericarp. It surrounds the part of the seeds. It is generally not consumed, but in citrus fruits, they make the main edible part like in oranges, the pulpy part, which has the juice vesicles make most of the endocarp.
Seed: Seed has three parts- the seed coat, the embryo, and the endosperm. The seed coat is developed from the female reproductive part, but the endosperm and embryo are developed through the cross-fertilization of both male and female units. The outermost covering is the seed coat that protects the seed. The next layer, the endosperm, provides nutrition to the embryo, which is the innermost part of the seed.
Classification of Fruits
There are basically two points for the classification of fruits:
One is by determining whether the carpels present in gynoecium are free or in a fused state.
And another is by determining one or more flowers takes part in the formation of fruit.
Types of Fruits
There are basically three types of fruits :
Simple
Aggregate
Composite
Simple Fruit: Simple fruits are those types of fruits that are developed from the monocarpellary ovary or multicarpellary syncarpous ovary and it is the only fruit that is formed by the gynoecium. Simple fruits are classified into two types :
Fleshy Fruits: The fruits whose wall is differentiated into epicarp, mesocarp, and endocarp. Fleshy fruits developed from superior or inferior syncarpous gynoecium.
Dry Fruits: The pericarp of dry fruits is usually dry and hard. Dry Fruits can not be described under these three layers of epicarp, mesocarp and endocarp. In some dry fruits the pericarp is found broken down and the seeds are scattered or dispersed.
Aggregate Fruits: Aggregate Fruits are the types of fruits that originate from the multicarpellary apocarpous ovary. This fruit becomes a fruitlet because each carpel is separated from one another in the apocarpous ovary. Aggregate fruits make a bunch of fruitlets which are known as etaerio.
Etaerio of follicles: In this type, the stigma is fused or joined in the carpellary ovary, and ovaries of ovules are separated like in Calotropis.
Etaerio of achenes: Strawberry and Lotus are Etaerio of achenes. In lotus, the thalamus is spongy and some achenes are embedded in it. In strawberries, the thalamus becomes fleshy and small achenes are on its surface.
Etaerio of berries: Annona is Etaerio of berries. In the etaerio of Annona, all the berries are arranged on the thalamus.
Etaerio of drupes: In Etaerio of drupes, many small drupes develop from different carpels. Example: Raspberry.
Composite Fruits: All composite fruits are mainly false fruits. Composite fruits generally have many ovaries and other floral parts combined to form the fruit. Composite fruits are of two types:
Sorosis: Sorosis fruits develop from spike, spadix or catkin inflorescence. Examples: Jackfruit.
Sycosis: Sycosis fruits develop from hypanthodium inflorescence. Example: Ficus species Peepal.
FAQs on Fruits Formation, Parts, and Types of Fruits
1. What is a fruit in botanical terms, and which part of the flower develops into it?
In botany, a fruit is defined as the mature or ripened ovary of a flowering plant, which develops after the process of fertilization. The wall of the ovary develops into the wall of thefruit, known as the pericarp, which encloses the seed or seeds that have developed from the ovules.
2. What are the main parts of a typical fruit?
A typical fruit consists of two main parts: the pericarp (the fruit wall) and the seeds. The pericarp is further differentiated into three distinct layers:
- Epicarp: The outermost layer, which forms the skin of the fruit.
- Mesocarp: The middle layer, which is often the fleshy, edible part of the fruit, like in a mango or peach.
- Endocarp: The innermost layer, which surrounds the seed. It can be hard and stony (as in a drupe) or papery.
3. How is a fruit formed after fertilisation in a flowering plant?
Fruit formation is triggered by fertilisation. After a pollen grain lands on the stigma (pollination), it germinates and its male gamete fuses with the egg cell inside the ovule. This fertilised ovule develops into a seed. The hormone signals produced by the developing seed stimulate the ovary to grow and mature. As the ovary enlarges, it transforms into the fruit, while other floral parts like petals, sepals, and stamens typically wither and fall off.
4. Can a fruit develop without fertilisation? Explain with an example.
Yes, a fruit can develop without fertilisation in a process called parthenocarpy. In such cases, the fruit is formed from the ovary without the stimulation of fertilisation, resulting in fruits that are typically seedless. A common example of a parthenocarpic fruit is the banana. This phenomenon can occur naturally or can be induced artificially using growth hormones.
5. What are the three main types of fruits based on their development?
Based on their development from the flower, fruits are classified into three main types:
- Simple Fruits: Develop from a single carpel or multiple fused carpels of a single flower. Examples include mango and tomato.
- Aggregate Fruits: Develop from multiple separate carpels of a single flower. This results in a cluster of small 'fruitlets', like in a raspberry or strawberry.
- Composite Fruits: Develop from a whole inflorescence (a cluster of flowers) rather than a single flower. Examples include pineapple and jackfruit.
6. What is the difference between a true fruit and a false fruit (pseudocarp)?
The key difference lies in which floral parts form the fruit. A true fruit develops exclusively from the mature ovary of a flower, like a mango or grape. In contrast, a false fruit, or pseudocarp, develops from the ovary along with other accessory floral parts, such as the thalamus or receptacle. A classic example of a false fruit is an apple, where the fleshy, edible part is the swollen thalamus, not the ovary wall.
7. Why is a tomato considered a fruit but is commonly used as a vegetable?
From a botanical standpoint, a tomato is a fruit because it develops from the ovary of a flower and contains seeds. Specifically, it is classified as a berry. Its common culinary use as a vegetable is based on its savoury flavour profile and how it is used in cooking, typically in main courses rather than desserts. This is a case where the botanical and culinary definitions differ.
8. What is the biological importance of fruit formation and dispersal?
The primary biological importance of a fruit is to protect the developing seeds and to aid in their dispersal. Dispersal is crucial for plants as it prevents overcrowding, reduces competition for resources with the parent plant, and allows the species to colonise new areas. Fruits have evolved various adaptations, such as being fleshy and colourful to attract animals or having wings for wind dispersal, to achieve this.
9. How do aggregate and composite fruits differ from simple fruits?
The difference is based on the number of ovaries and flowers involved. A simple fruit develops from a single ovary of a single flower. An aggregate fruit develops from multiple, separate ovaries within the same single flower, forming a collection of fruitlets (e.g., raspberry). A composite fruit is even more complex, developing from the ovaries of an entire cluster of flowers (an inflorescence), which fuse together to form one large fruit (e.g., pineapple).
10. How does the structure of the pericarp relate to a fruit's function?
The structure of the pericarp is directly related to the fruit's primary functions of seed protection and dispersal. In fleshy fruits like berries, a pulpy and often sweet mesocarp attracts animals, which eat the fruit and disperse the seeds. In dry fruits like nuts, the entire pericarp becomes hard and woody, providing robust protection for the seed inside. In other dry fruits, the pericarp may develop structures like wings or hooks to aid in dispersal by wind or by attaching to animal fur.
