Fruit and Seed physiology | Botany Optional for UPSC PDF Download

Introduction

Seeds and fruits are fundamental components of plant reproduction, arising from the intricate process of fertilization or sexual reproduction in plants. In angiosperms, the ovary transforms into what we recognize as a fruit, while the ovules develop into seeds encapsulated within that very fruit. This article delves into the world of seeds and fruits, dissecting these botanical entities to provide a comprehensive understanding. Fruits are not only flavorful but also brimming with nutrients, some even masquerading as vegetables, such as tomatoes. A fruit can be dissected into the pericarp, which encompasses various protective layers, and the seeds nestled within. The pericarp, in turn, comprises three layers: the outermost exocarp, the juicy mesocarp, and the innermost endocarp. To navigate this botanical landscape, let's explore seeds and fruits in greater detail.

Development of a Fruit

Once pollination and fertilization have successfully transpired, a zygote is formed, marking the commencement of fruit development. During this process, the ovary's outer wall undergoes transformation into the pericarp, while the seeds take shape within the developing fruit.

• Exocarp: It is the outermost layer which is formed from the outer layer or the epidermis
• Mesocarp: Is the second or the middle layer which is often juicy and varies in thickness in different fruits
• Endocarp: It is the innermost layer and also is different in different kinds of fruits

Types of Fruits

Fruits exhibit considerable diversity and can be categorized in several ways. The most common classification includes true and false fruits, as well as simple, aggregate, and multiple fruits.

True and False Fruits

• True Fruits: These fruits emerge solely from the ovary, with ovules as their sole constituents. Other parts of the flower do not contribute to this type of fruit.
• False Fruits: False fruits, in contrast, are formed from the matured ovary along with additional floral components, such as the base or receptacle and the perianth.

Simple, Aggregate, Multiple, and Accessory Fruits

• Simple Fruits: These fruits originate from a single pistil and are further categorized into fleshy and dry fruits based on the nature of their pericarp.
  • Fleshy Fruits: These fruits boast a juicy pericarp and come in various forms:
    • Drupe: Characterized by a thin exocarp, a thick and juicy mesocarp, and a stony endocarp. Examples include mangoes, plums, and coconuts.
    • Berry: In this type, the endocarp is absent, and seeds are dispersed within the mesocarp. Common examples encompass grapes, bananas, and tomatoes.
    • Pome: A false fruit where the thalamus is an integral part. Apples and pears exemplify this category.
• Dry Fruits: These fruits lack a juicy or thick pericarp and fall into two subcategories:
  • Dehiscent Dry Fruits: These fruits spontaneously burst to release their seeds. Varieties include follicles, legumes, capsules, and siliquas.
  • Indehiscent Dry Fruits: Unlike dehiscent fruits, these do not burst to disperse their seeds. Examples consist of achenes, caryopses, samaras, nuts, and cypselas.
• Aggregate Fruits: These fruits develop from multiple separate pistils clustered together within a single flower. This cluster is termed an etaerio, with raspberries serving as a classic example.
• Multiple Fruits: When an entire inflorescence transforms into a single fruit, it is referred to as a multiple fruit. Pineapples, figs, mulberries, and jackfruits belong to this category.

Seeds

Following successful fertilization, the mature ovule starts evolving into a seed, comprising several crucial components:

• Seed Coat: Formed from the integuments of the ovule, the seed coat encases the seed. It includes a hilum, a scar marking the point where the ovule connected to the ovary's wall. A micropyle, a small pore, allows the embryo to germinate when suitable conditions prevail.
• Cotyledons: Monocots possess a single cotyledon, while dicots have two. These cotyledons act as appendages aiding in nutrient absorption from the endosperm.
• Endosperm: This triploid tissue results from the fusion of a haploid male nucleus and a diploid vegetative nucleus. It plays a pivotal role in nourishing the developing embryo and can classify seeds into endospermic and non-endospermic categories.
• Embryo: Comprising a central axis with a root apex (radicle) and a shoot apex (hypocotyl), the embryo forms the foundation for the plant's future growth. The radicle gives rise to the root, while the hypocotyl forms the shoot.