Introduction

In flowering plants the organ of reproduction is the flower. A typical flower has four different parts like sepals, petals, stamens and carpel. Plants carry sexual reproduction with the help of flowers. The fruit which develops after fertilisation bear seeds which germinate and start the next generation. The plants of the next generation always show genetic variations.Such plants are better adapted to the changing environment.These organs are just as crucial to plants as humans for survival.  

Plant Body

The plant body of an angiosperm has two types of parts namely vegetative parts and reproductive parts.

Vegetative parts are roots, stems, leaves and branches which make the general plant body.

The reproductive part is a flower in all angiosperms. Flowers are converted into fruits and inside of them seeds are present.

In this article reproductive structure of angiosperms will be discussed 

Flower

A flower is a distinctive feature of all flowering plants, and it is an outgrowth of the reproductive stalk. Flowers are visually appealing and come in various sizes, shapes and colours. Colourful flowers attract pollinators that aid in pollen transmission. Sometimes the flowers are colourless but produce fragrance to attract the pollinators.

Flowers pollinated by wind are generally colourless and fragrance less as these need not to attract pollinators.

Structure of the flower

Flower has four parts arranged in whorls.These are

1. Sepals- Generally green in colour and protect the flowers till they are in buds.
2. Petals- These are either colourful or colourless and nectaries may be present at their base. Their main function is to attract insects, birds, etc. for pollination.
3. Stamen -It is the male portion of the flower and is made up of:

      Anthers – Pollen-producing organs. Pollen is the male gametophyte of a flowering plant which produces two male gametes on germination.

      Filament- It is the stalk that holds the anthers in place (makes the anther accessible to pollinators). It may vary in length in different flowers.

4. Pistil – It is the female portion of the flower and is made up of:

   Stigma- The sticky, receptive tip of the pistil that catches pollen and helps in pollen germination.

   Style- The tube-shaped link between the stigma and the ovary is known as the style which elevates the stigma to help catch pollen.

   Ovary- The basal part of the pistil which contains one or many ovules. The ovary forms fruit and ovules inside the ovary form seeds after the process of fertilisation. That’s why in angiosperms seeds are covered by the fruits.

Development of flower

• Flower development is very standardised since it is under substantial genetic control. It is broken down into several stages, including floral induction, floral meristem creation and flower organ development. A gene regulatory network made up of connecting genes and its protein products are responsible for precise control of the many stages of flower development.
• Flowering-time genes, triggered by developmental signals and environmental factors like plant age, day length and temperature are near the top of the floral Gene Regulatory Network hierarchy.
• Flowering-time genes activate meristem identity genes, mediating the transition from vegetative and reproductive development.
• Upstream regulators of floral organ identity genes and meristem identity genes transform the vegetative meristem to floral meristems.

Fruits

The fruit is an ovary that has matured or ripened and usually contains seeds. So for botanists fruit is a structure which develops from the ovary but for a common man fruit means which are consumed raw and are sweet or sour in taste. On the other hand, vegetables can be made up of leaves, leaf petioles, specialised leaves, stalks, stems and roots, flowers, flower buds and other plant elements.

Structure of the fruit

• The two most essential parts are a fruit are –

        (i) Fruit wall (pericarp)

        (ii)Seeds 

• The structure and thickness of the pericarp vary from fruit to fruit
• The pericarp comprises three layers: the outer epicarp, middle mesocarp, and inner endocarp
• In fruits the layers of pericarp vary in structure. The mesocarp is the sweet, moist and edible centre in some of the fruits, while the endocarp is hard. In some fruits epicarp and mesocarp are soft and fleshy with hard endocarp, in some the endocarp may even be soft. These three layers are difficult to distinguish in dry fruits

Development of fruit

• The ovary of the flower typically transforms into the fruit after its fertilisation
• The seeds and developing embryos are protected by the fruit, which encloses them
• Fruits can be of two different types –

  True fruits – These develop from the ovary of the flowers e.g. mango, grapes, etc. These are of following types-

   (i) Simple fruits grow from a sole or fused carpel of one ovary

   (ii)  An aggregation fruit grows from many carpels in a single bloom

   (iii)  Accessory fruits come from a different portion of the flower along with the ovary

     False fruits- In these fruits the edible part develops from a different part of the flower other than the ovary e.g.,apple, guava,etc.

Seed: For many higher plants, the seed is the starting and the conclusion of their life cycle. Seeds are extremophiles, which can withstand extremes of temperature, cold, desiccation, and air pressure. Seeds are the most excellent means of survival for species and populations because of these characteristics. 

The ovule will grow into a seed after fertilisation. The source would be distributed from the parent plant and germinate, resulting in the growth of a new plant.

In monocots the seeds have only one cotyledon along with endosperm and embryonic shoot. In dicots the seed consists of the two cotyledons, embryonic axis and seed coat 

Structure of seed

A typical dicot seed has the following structures:

1. Seed coat – It has two components, testa and tegmen.
2. Micropyle – It is a tiny pore in the seed’s outer coating that permits water to enter through.
3. Cotyledon – It develops the embryonic leaves and holds the seed’s nutritional storage mostly in dicot seeds.
4. Endosperm- It is nutritive tissue in monocot seeds but in dicot seeds it is generally reduced.
5. The embryonic shoot has plumule and radicle.                                   

Development of seed

• The seed develops from the ovule, is covered by a seed coat which is made up of the ovule sac’s integuments
• The seed is formed from the mature ovule. Seed coats, cotyledons, endosperm and a single embryo are all found in an ordinary seed
• The combination of dormancy releasing variables, which influence the end of inactivity, determine seed germination in a specific setting and season

Conclusion

Plants are living things that are critical to our survival on this planet. They supply food for people and other animals and allow us to breathe by turning carbon dioxide from our exhaled air into oxygen. There are over 80,000 edible plant species on the planet. So sexual reproduction shown by the plants is the key for the development of better suited plant species. Hence, flowers becomes one of the essential part of the plants.