Fruit Formation in Flowering Plants Structure and Classification

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.