Morphology Of Flowering Plants Class 11 Biology Chapter 5 Notes

The Root System in Plants

The root system in plants plays a crucial role in supporting various functions necessary for a plant’s growth, development, and survival. It differs in structure and function between dicotyledonous and monocotyledonous plants and can also exhibit variations like adventitious roots. Here are some key aspects of the root system in plants:

1. Primary Root and Taproot System:

In many dicotyledonous plants, the primary root, which develops from the radicle, extends into the soil. It is referred to as the primary root.
The primary root gives rise to lateral roots of different orders, known as secondary, tertiary, etc. roots.
The primary root and its branches collectively form the taproot system. An example of a plant with a taproot system is the mustard plant.

2. Fibrous Root System:

Monocotyledonous plants typically have a different root structure. The primary root in monocots is usually short-lived.
Instead of a primary root, monocots develop a large number of roots that originate from the base of the stem.
This type of root system is known as the fibrous root system. Wheat plants are an example of plants with a fibrous root system.

3. Adventitious Roots:

In some plants, such as grasses, Monstera, and banyan trees, roots can arise from parts of the plant other than the radicle.
These roots are termed adventitious roots and may emerge from stems, leaves, or other plant organs.
Adventitious roots provide additional support and absorb water and nutrients from the environment.

Functions of the Root System:

Absorption: One of the primary functions of the root system is to absorb water and essential minerals from the soil. This water and these minerals are vital for the plant’s growth and metabolic processes.
Anchorage: Roots anchor the plant securely in the soil, providing stability and preventing it from being uprooted by wind or other forces.
Storage: Roots can store reserve food materials, primarily in the form of carbohydrates, which can be used during periods of limited photosynthesis or to support plant growth.
Synthesis of Plant Growth Regulators: Roots are involved in the production of various plant growth regulators, such as hormones, which influence processes like growth, development, and responses to environmental stimuli.

The root system is a critical component of a plant’s overall structure and function, working in tandem with the shoot system (above-ground parts) to enable the plant to adapt and thrive in its specific environment.

Regions of the Root in Plants

The root of a plant has distinct regions, each with specific functions that contribute to its growth, development, and overall performance in the soil. These regions are vital for absorbing water and minerals, providing structural support, and protecting the root apex. Here are the key regions of a plant root:

1. Root Cap:

The root cap is a thimble-like structure located at the apex (tip) of the root.
Its primary function is to protect the delicate and actively growing root tip as it penetrates the soil.
The root cap also secretes a slimy substance that lubricates the root’s passage through the soil.

2. Region of Meristematic Activity:

Just a few millimeters above the root cap is the region of meristematic activity.
In this region, the cells are small, thin-walled, and have dense protoplasm.
These cells divide rapidly, and this region is responsible for primary growth by adding new cells to the root.

3. Region of Elongation:

Above the region of meristematic activity is the region of elongation.
In this region, the cells derived from the meristematic zone undergo rapid elongation and enlargement.
The primary function of this region is to increase the length of the root by adding cells lengthwise.

4. Region of Maturation:

Proximal (closer to the base) to the region of elongation is the region of maturation.
In this zone, cells gradually differentiate and mature, taking on specific functions.
Root tissues in this region develop specialized structures, such as root hairs, for specific tasks.

5. Root Hairs:

Root hairs are delicate, thread-like structures that arise from some of the epidermal cells in the region of maturation.
These hair-like extensions greatly increase the surface area of the root.
Root hairs are responsible for absorbing water and minerals from the soil by increasing the root’s capacity for nutrient uptake.

Features That Distinguish a Stem from a Root

The stem is a vital part of a plant, serving various functions such as support, transport, and reproduction. It is distinct from the root in several ways. Here are the key features that distinguish a stem from a root:

1. Position and Function:

The stem is the ascending part of the plant’s axis, and it typically grows above the ground.
It plays a central role in bearing branches, leaves, flowers, and fruits.
Stems are responsible for elevating leaves to receive sunlight for photosynthesis and for providing a framework for reproductive structures like flowers and fruits.

2. Development:

Stems develop from the plumule, which is the embryonic shoot of a germinating seed.
Root development, on the other hand, begins from the radicle, the embryonic root.

3. Nodes and Internodes:

The stem has nodes and internodes. Nodes are the specific points on the stem where leaves, branches, or other structures, like flowers and fruits, are attached.
Internodes are the segments of the stem between two adjacent nodes.

4. Buds:

Stems often bear buds, which are small, undeveloped or embryonic shoots.
Buds may be found at different locations on the stem, including at the tips (terminal buds) or in the leaf axils (axillary buds).

5. Color and Texture:

Young stems are generally green due to the presence of chlorophyll and are soft and herbaceous.
As they mature, some stems may become woody and develop a dark brown or woody texture. This transition often occurs in perennial plants as they age.

6. Functions:

The primary function of the stem is to provide support for the plant and to position leaves for maximum sun exposure.
Stems also serve as conduits for the transport of water, minerals, and photosynthates (sugars and other organic compounds) throughout the plant.
Some stems are specialized for storing food, such as in the case of rhizomes and tubers.
In certain plants, stems may perform roles in protection, like thorns or spines, and in vegetative propagation, where new plants can sprout from stem cuttings.

Structure of a Typical Leaf

A typical leaf is a crucial plant organ primarily responsible for photosynthesis. It consists of several essential parts, each with specific functions. Here’s an overview of the structure of a typical leaf:

Leaf Base:
- The leaf base is the lowermost part of the leaf where it attaches to the stem.
- It often contains two small leaf-like structures called stipules.
- In monocotyledonous plants, the leaf base may expand into a sheath that partially or wholly encircles the stem.
- In some leguminous plants, the leaf base may become swollen, forming a pulvinus.
Petiole:
- The petiole is a slender, stalk-like structure that connects the leaf base to the leaf blade or lamina.
- It plays a crucial role in positioning the leaf blade to capture light efficiently.
- The length and flexibility of the petiole can vary, allowing the leaf blade to flutter in the wind, promoting cooling and gas exchange on the leaf surface.
Lamina (Leaf Blade):
- The lamina, also known as the leaf blade, is the expanded, green, and often flattened part of the leaf.
- It is the primary site for photosynthesis, where chloroplasts capture light energy to convert carbon dioxide and water into glucose.
- Veins and veinlets run through the lamina, providing structural support and serving as conduits for water, minerals, and food materials.
- The midrib is the central, prominent vein in the lamina, from which smaller veins branch out.
- The shape, margin, apex (tip), surface texture, and extent of incisions (if present) on the lamina can vary significantly among different types of leaves.

The arrangement of leaves on a plant is typically in an acropetal order, meaning that younger leaves are found near the growing tip of the stem, while older leaves are closer to the base. Leaves are essential for capturing light energy, the primary source of energy for plants, and for conducting photosynthesis, which is crucial for producing the plant’s food.

Venation in Leaves

Venation refers to the arrangement of veins and veinlets in the lamina (leaf blade) of a leaf. It is an important characteristic used to identify and classify different plant species. There are two main types of venation: reticulate and parallel.

Reticulate Venation:
- Reticulate venation is characterized by the formation of a network of veins and veinlets within the leaf lamina.
- In this type of venation, the veins and veinlets intersect and branch to form a complex pattern resembling a net or mesh.
- Reticulate venation is typical of dicotyledonous plants, which include many familiar trees, shrubs, and herbaceous plants. Examples of plants with reticulate venation include mango, rose, and maple leaves.
Parallel Venation:
- Parallel venation is characterized by the presence of veins that run side by side in a parallel arrangement within the leaf lamina.
- In this type of venation, the veins do not form a network but instead run in a parallel fashion from the base of the leaf to the tip.
- Parallel venation is a distinguishing feature of monocotyledonous plants, which include grasses, lilies, and orchids. Examples of plants with parallel venation include rice, wheat, and corn leaves.

The type of venation can be observed by examining the pattern of veins and veinlets on the surface of the leaf. Reticulate venation is generally considered more primitive, while parallel venation is a more specialized adaptation that evolved in response to specific ecological and physiological factors.

Types of Leaves

Leaves are one of the most important vegetative organs of plants, and they come in various forms and arrangements. Two common types of leaves are simple leaves and compound leaves. Additionally, compound leaves can be further categorized into pinnately compound leaves and palmately compound leaves.

Simple Leaves:
- Simple leaves have a single, undivided blade or lamina. The blade may be entire (smooth and without incisions) or have slight irregularities.
- If there are incisions in the blade, they do not reach the midrib of the leaf.
- Simple leaves have a petiole, which is the stalk that attaches the leaf to the stem or branch.
- Examples of plants with simple leaves include mango, rose, and hibiscus.
Compound Leaves:
- Compound leaves are divided into multiple leaflets, each resembling a small, simple leaf. These leaflets are attached to a common petiole or rachis.
- Compound leaves can be distinguished from simple leaves by the presence of leaflets.
- Compound leaves have a bud in the axil of the main petiole but not in the axil of individual leaflets.
- Examples of plants with compound leaves include neem (pinnately compound) and silk cotton (palmately compound).
a. Pinnately Compound Leaves:
- In pinnately compound leaves, multiple leaflets are arranged along a central axis or rachis, resembling a feather or a comb.
- The leaflets are attached to the rachis, and the rachis itself connects to the main petiole.
- The rachis is equivalent to the midrib of a simple leaf.
- Example: Neem tree leaves.
b. Palmately Compound Leaves:
- In palmately compound leaves, several leaflets are attached at a common point, which is the tip of the petiole.
- The leaflets radiate from a single point, similar to the fingers of a hand. The arrangement resembles the shape of a palm.
- The palmately compound leaf lacks a rachis, and the leaflets are directly attached to the petiole.
- Example: Silk cotton tree leaves.

The type of leaf arrangement is a characteristic feature used in plant identification and classification. It also reflects the diversity of adaptations that plants have evolved to suit their ecological niches and environmental conditions.

Phyllotaxy (Arrangement of Leaves)

Phyllotaxy refers to the specific pattern or arrangement of leaves on a stem or branch of a plant. The arrangement of leaves is an important botanical characteristic and can be classified into three main types: alternate, opposite, and whorled. These patterns determine how leaves are positioned relative to each other along the stem.

Alternate Phyllotaxy (Alternate Leaves):
- In an alternate phyllotaxy, a single leaf arises at each node, and leaves are positioned alternately along the stem.
- Each leaf is located at a different height along the stem, forming a spiral arrangement.
- Examples of plants with alternate phyllotaxy include the China rose, mustard, and sunflower.
Opposite Phyllotaxy (Opposite Leaves):
- In an opposite phyllotaxy, two leaves arise at each node, and they are positioned in pairs opposite to each other.
- The leaves are located at the same height on the stem, directly across from each other.
- This arrangement creates a symmetrical appearance.
- Examples of plants with opposite phyllotaxy include Calotropis and guava.
Whorled Phyllotaxy (Whorled Leaves):
- In a whorled phyllotaxy, more than two leaves arise at each node and form a circular or whorled pattern around the stem.
- Leaves are positioned in a ring or cluster at each node.
- The number of leaves in a whorl can vary depending on the plant species.
- An example of a plant with whorled phyllotaxy is Alstonia.

The arrangement of leaves on a plant is influenced by various factors, including genetic factors and environmental conditions. Phyllotaxy is an important feature for plant identification and classification. Different phyllotactic patterns can affect the exposure of leaves to light and their efficiency in photosynthesis. It is also used as a diagnostic feature in plant taxonomy and botany.

Inflorescence: Types and Arrangement of Flowers

An inflorescence refers to the arrangement of flowers on a floral axis, which is a modified shoot with the shoot apical meristem transformed into a floral meristem. The way in which flowers are organized on the floral axis can be categorized into two major types: racemose and cymose inflorescences.

Racemose Inflorescence:

In racemose inflorescences, the main axis (floral axis) continues to grow, and flowers are borne laterally in an acropetal (from base to apex) succession.
This type of inflorescence allows the main axis to elongate and produce flowers at the nodes along the axis.
Flowers in racemose inflorescences are typically arranged in a more indeterminate pattern.
Examples of racemose inflorescences include the raceme (e.g., mustard, radish), spike (e.g., wheat, barley), and panicle (e.g., rice, oats).

Cymose Inflorescence:

In cymose inflorescences, the main axis terminates in a flower, and the growth of the axis is limited.
In this type, the flowers are borne in a basipetal (from apex to base) order, meaning the terminal or youngest flower is at the top, and older flowers are located below.
Cymose inflorescences tend to have a more determinate pattern, as the main axis terminates in a flower.
Examples of cymose inflorescences include the cyme (e.g., jasmine, forget-me-not) and umbel (e.g., onion, coriander).

The choice between racemose and cymose inflorescences is determined by genetic factors and is influenced by the plant’s species and environmental conditions. The arrangement of flowers in an inflorescence can affect the distribution of pollen, timing of flowering, and other reproductive strategies of the plant.

The Flower: Structure and Types

The flower is the reproductive unit in angiosperms (flowering plants) and plays a central role in sexual reproduction. It consists of four distinct whorls or parts that are arranged successively on the swollen end of the stalk or pedicel known as the thalamus or receptacle. These four whorls are the calyx, corolla, androecium, and gynoecium.

Calyx: The calyx is the outermost whorl of the flower and is typically green in color. It consists of sepals that are usually green and enclose the inner parts of the flower when it is in bud. The primary function of the calyx is to protect the developing flower bud.

Corolla: The corolla is the next whorl and is made up of petals. Petals are often colorful and serve to attract pollinators like insects or birds. The arrangement of petals can vary greatly among different plant species, contributing to the diversity and beauty of flowers.

Androecium: The androecium is the third whorl and consists of stamens. Stamens are male reproductive structures, each composed of an anther at the tip, which produces pollen, and a filament that supports the anther. The androecium plays a crucial role in fertilization by producing and releasing pollen.

Gynoecium: The gynoecium is the innermost whorl and includes the female reproductive structures. It typically consists of one or more carpels, each of which has three main parts: the stigma (the receptive surface for pollen), the style (a slender stalk that connects the stigma to the ovary), and the ovary (the enlarged basal part where ovules are located). The gynoecium is responsible for producing and nurturing seeds.

Bisexual and Unisexual Flowers: Flowers can be categorized as bisexual when they contain both androecium and gynoecium. Unisexual flowers, on the other hand, have either stamens (male) or carpels (female) but not both.

Symmetry of Flowers: Flowers can exhibit different types of symmetry. Actinomorphic flowers have radial symmetry, meaning they can be divided into similar halves by cutting through the center in multiple directions. Zygomorphic flowers have bilateral symmetry, meaning they can be divided into two similar halves in one particular vertical plane. Asymmetric flowers cannot be divided into two similar halves along any vertical plane.

Floral Appendage Arrangement: Flowers can have a trimerous arrangement when their floral appendages (e.g., sepals, petals, stamens) occur in multiples of three. Tetramerous flowers have floral appendages in multiples of four, and pentamerous flowers have them in multiples of five.

Bracteate and Ebracteate Flowers: Flowers with bracts, reduced leaf-like structures at the base of the pedicel, are called bracteate. Flowers without bracts are referred to as ebracteate.

Position of Floral Organs: Flowers can be described based on the position of the calyx, corolla, and androecium in relation to the ovary on the thalamus. Hypogynous flowers have the gynoecium positioned above the other parts, and their ovary is described as superior. Perigynous flowers have the gynoecium in the center and other parts located on the rim of the thalamus, and the ovary is described as half-inferior. Epigynous flowers have the ovary positioned below the other parts, and the ovary is described as inferior.

Understanding the structure and types of flowers is essential for plant identification and for the study of plant reproduction, pollination, and floral development.

Parts of a Flower

1. Calyx: The Sepal Whorl

The calyx is the outermost whorl of the flower and is primarily composed of leaf-like structures called sepals. The calyx serves several important functions in the life of a flower. The key characteristics of the calyx are as follows:

Sepals: The individual members of the calyx are called sepals. Sepals are typically green, which is the common color for most calyxes, but they can sometimes exhibit colors that are different from the petals. Their primary role is to encase and protect the inner floral structures when the flower is in the bud stage. Additionally, sepals can help in attracting pollinators by offering a contrasting color to the petals.
Gamosepalous vs. Polysepalous: The calyx can take on different forms based on the arrangement of sepals. In a gamosepalous calyx, the sepals are fused or united, forming a single structure that encases the floral bud. In contrast, a polysepalous calyx has sepals that remain distinct or free from each other, with individual sepals encircling the bud.

The calyx, along with the corolla (petals), plays a significant role in the flower’s appearance and attractiveness to pollinators. It helps protect the developing flower bud and then opens to allow the mature flower to bloom. The diversity in calyx characteristics contributes to the vast array of flower shapes, sizes, and colors seen in the plant kingdom.

2. Corolla: The Petal Whorl

The corolla is the second whorl in the flower, located inside the calyx, and is made up of the petals. The primary role of the corolla is to attract pollinators, such as insects or birds, to the flower. Key features of the corolla include:

Petals: Individual members of the corolla are called petals. Petals are typically the most visually striking part of the flower, often displaying bright and attractive colors. These vibrant colors and various shapes serve to attract pollinators, ultimately facilitating pollination and reproduction in the plant.

Gamopetalous vs. Polypetalous: Similar to the calyx, the corolla can exist in different forms based on the arrangement of petals. In a gamopetalous corolla, the petals are fused or united to form a single structure, enhancing the visual appeal of the flower. On the other hand, a polypetalous corolla consists of individual, separate petals.

Variation in Shape and Color: The corolla can exhibit a wide range of shapes, including tubular, bell-shaped, funnel-shaped, or wheel-shaped, depending on the plant species. Petal colors can vary significantly, and they are often adapted to the specific pollinators the plant aims to attract.

Aestivation: Aestivation is the mode of arrangement of sepals or petals within a floral bud concerning the other members of the same whorl. The main types of aestivation are as follows:

Valvate Aestivation: In valvate aestivation, sepals or petals in a whorl merely touch each other at the margins without overlapping.
Twisted Aestivation: In this arrangement, one margin of the appendage of a sepal or petal overlaps the next one, forming a twisted pattern. This arrangement can be seen in many plants, including Calotropis.
Imbricate Aestivation: Sepals or petals have overlapping margins, but the overlap doesn’t follow a specific direction. It is seen in flowers like Cassia and Gulmohur.
Vexillary or Papilionaceous Aestivation: This type of aestivation is specific to certain plants, such as pea and bean flowers. In these flowers, there are five petals: the largest one (standard) overlaps the two lateral petals (wings), which in turn overlap the two smallest anterior petals (keel).

The shape and arrangement of the corolla, along with its colors, are important factors in the diversity of flower appearances and their effectiveness in attracting specific pollinators.

3. Androecium: The Male Reproductive Whorl

The androecium is the third whorl of the flower and is composed of stamens, which represent the male reproductive organs of the flower. Key features of the androecium include:

Stamens: Stamens are the individual members of the androecium. Each stamen is made up of two main parts: a stalk or filament and an anther.

Anther: The anther is the terminal, typically bilobed structure of the stamen. Each lobe of the anther contains two chambers known as pollen-sacs. Pollen grains, which are vital for pollination, are produced within these pollen-sacs.

Pollen Production: The primary function of the androecium is to produce and release pollen. Pollen is a crucial element in plant reproduction as it carries the male gametes (sperm cells) necessary for fertilizing the female gametes in the ovule.

Sterile Stamens: Occasionally, some stamens in a flower may be sterile and not directly involved in pollen production. These sterile stamens are called staminodes.

Attachment and Arrangement: Stamens in a flower can be attached to various floral parts. When stamens are attached to petals, they are referred to as epipetalous, as seen in the case of brinjal flowers. If they are attached to the perianth, they are described as epiphyllous, as in the flowers of lilies.

Degree of Union: Stamens in a flower may either remain free (polyandrous) or be united in different degrees. The degree of union among stamens can vary, leading to several categories:

Monoadelphous: Stamens are united into one bundle. This arrangement is observed in flowers like China rose.
Diadelphous: Stamens are united into two bundles, seen in flowers like peas.
Polyadelphous: Stamens are united into more than two bundles, common in plants like citrus.

Variation in Filament Length: In some flowers, there may be variations in the length of the filaments within a single flower. This variation can serve various purposes, including optimizing the position of the anthers for effective pollination. For example, Salvia and mustard are known for this feature.

The androecium’s role in a flower is crucial for producing and releasing pollen, which is necessary for fertilization and seed development. It plays a key role in the reproductive success of the plant.

4. Gynoecium: The Female Reproductive Whorl

The gynoecium is the fourth and innermost whorl of the flower and is the female reproductive part. It is composed of one or more carpels. The carpel consists of three main parts: the stigma, style, and ovary. The functions and features of the gynoecium include:

Carpels: The gynoecium consists of one or more carpels. Each carpel represents a potential seed-bearing unit, and it contains the female reproductive structures.

Stigma: The stigma is the receptive surface at the tip of the carpel. Its role is to capture pollen grains during pollination. The stigma is the first point of contact between the male (pollen) and female (ovule) reproductive structures.

Style: The style is an elongated tube-like structure that connects the stigma to the ovary. It serves as a passage for the pollen to travel from the stigma to the ovary, where fertilization occurs.

Ovary: The ovary is the basal, usually enlarged part of the carpel. It contains the ovules, which are potential seeds. Once fertilization occurs, the ovary develops into a fruit, and the ovules develop into seeds.

Number of Carpels: Depending on the flower species, the number of carpels in the gynoecium can vary. Flowers may have a single carpel (simple pistil) or multiple carpels (compound pistil).

Apocarpous and Syncarpous: In some flowers, multiple carpels may be free, not fused together (apocarpous), such as in lotus and rose. In other cases, carpels are fused together (syncarpous), like in mustard and tomato.

Placentation: Placentation refers to the arrangement of ovules within the ovary. Several types of placentation exist:

Marginal Placentation: The placenta forms a ridge along the ventral suture of the ovary, and the ovules are borne on this ridge, forming two rows. An example is seen in pea.
Axile Placentation: The placenta is axial, and the ovules are attached to it in a multilocular ovary. This type is observed in plants like China rose, tomato, and lemon.
Parietal Placentation: The ovules develop on the inner wall of the ovary or on the peripheral part. The ovary is typically one-chambered but appears two-chambered due to the formation of a false septum. Mustard and Argemone are examples.
Free Central Placentation: The ovules are borne on the central axis, and septa are absent. This type is observed in flowers like Dianthus and Primrose.
Basal Placentation: The placenta develops at the base of the ovary, and a single ovule is attached to it. Sunflower and marigold exhibit basal placentation.

The gynoecium plays a crucial role in the reproductive process by housing the female reproductive structures and developing into fruits once fertilization occurs. The arrangement of the ovules within the ovary, known as placentation, can vary among different plant species.

The Fruit: A Mature Ovary

The fruit is a significant characteristic of flowering plants (angiosperms) and is the mature or ripened ovary that develops after fertilization. It plays a vital role in the life cycle of plants as it protects and aids in the dispersal of seeds. Here are some key features of the fruit:

Mature Ovary: The fruit is essentially the mature ovary of a flower. After pollination and fertilization, the ovule within the ovary develops into a seed, and the ovary itself matures into a fruit.

Parthenocarpic Fruit: In some cases, a fruit can develop without the need for fertilization of the ovary. Such fruits are known as parthenocarpic fruits.

Pericarp: The fruit is typically composed of two main parts: the pericarp and the seeds. The pericarp is the wall or outer covering of the fruit. It can be either dry or fleshy, depending on the type of fruit.

Dry or Fleshy: Fruits are classified based on the nature of the pericarp. Dry fruits have a relatively thin and papery pericarp, while fleshy fruits have a thick and succulent pericarp.

Differentiated Pericarp: In some fleshy fruits, the pericarp is further differentiated into three distinct layers:

Epicarp: The outermost layer, often thin and protective.
Mesocarp: The middle layer, which is the fleshy and edible part in many fruits.
Endocarp: The innermost layer, which can sometimes be hard or stony.

Drupe: Certain fruits, like mango and coconut, are categorized as drupes. Drupes develop from monocarpellary superior ovaries and typically contain one seed. In a mango, the pericarp is well-differentiated into an outer thin epicarp, a middle fleshy and edible mesocarp, and an inner stony and hard endocarp. In the case of a coconut, which is also a drupe, the mesocarp is fibrous.

Fruits serve several essential functions in the plant’s life cycle, including the protection and dispersal of seeds. They come in various forms, sizes, and types, and can be dry or fleshy, simple or complex, and are a fascinating area of study in plant biology.

The Seed: A Vital Plant Structure

Seeds are vital structures in the life cycle of flowering plants (angiosperms). They serve as the primary means of reproduction and dispersal for many plant species. Here are some key features of seeds:

Seed Coat: Each seed is enclosed within a protective layer known as the seed coat. The seed coat provides physical protection for the developing embryo and the stored food reserves within the seed.

Embryo: The embryo is the young, undeveloped plant within the seed. It consists of several essential parts:

Radicle: The radicle is the embryonic root of the plant. It is the first structure to emerge during germination and develops into the primary root system of the mature plant.
Embryonal Axis: The embryonal axis is the central axis of the embryo. It typically consists of the radicle, hypocotyl (the region between the radicle and cotyledons), and the epicotyl (the region above the cotyledons).
Cotyledons: Cotyledons are the seed leaves of the embryo. The number of cotyledons varies between plant species. In some plants, there is only one cotyledon (monocotyledon), while in others, there are two cotyledons (dicotyledon). Cotyledons play a crucial role in the early growth and development of the seedling. In dicots, the cotyledons often serve as the first leaves of the emerging seedling, providing nutrients and energy for initial growth until true leaves develop.

The process of seed development begins when the ovule is fertilized by pollen. The fertilized ovule develops into a mature seed, which may remain dormant for a period until the right conditions for germination occur.

Seeds are vital for plant propagation and are dispersed in various ways, including wind, water, animals, and humans. They contain the genetic information and resources necessary for a new plant to grow and develop.

1. Structure of a dicotyledonous seed

Seed Coat (Testa and Tegmen): The outermost covering of the seed is the seed coat, which consists of two layers, the outer testa and the inner tegmen. These layers provide protection to the inner seed components.
Hilum: The hilum is a scar or mark on the seed coat where the seed was attached to the fruit or the placenta of the ovary. It serves as the point of attachment.
Micropyle: Located above the hilum, the micropyle is a small pore or opening in the seed coat. It allows for the entry of water and gases during the germination process.
Embryo: The embryo is the young, undeveloped plant contained within the seed. It consists of several parts:
- Embryonal Axis: The embryonal axis is the central axis of the embryo. It includes the radicle (embryonic root), hypocotyl (the region between the radicle and cotyledons), and epicotyl (the region above the cotyledons). The radicle is the first structure to emerge during germination.
- Cotyledons: Dicotyledonous seeds typically have two cotyledons, which are the seed leaves. They often store reserve food materials. In some seeds, cotyledons may be fleshy and serve as a source of nutrients during germination.
Plumule: The plumule is the part of the embryo found at the upper end of the embryonal axis. It represents the shoot or the future stem of the plant.
Endosperm: In some dicotyledonous seeds, such as castor, the endosperm is a tissue that stores food materials. It is formed as a result of double fertilization, providing nutrients for the developing embryo. In other dicotyledonous seeds like beans, peas, and gram, the endosperm is not present in mature seeds, and the cotyledons take on the role of storing food reserves.

This structure of a dicotyledonous seed contains all the essential components for the growth and development of a new plant when the seed germinates under favorable conditions.

2. The structure of a monocotyledonous seed

Seed Coat: In monocotyledonous seeds, the seed coat is often membranous and may be fused with the fruit wall. It provides protection to the internal seed components.
Endosperm: Monocotyledonous seeds are generally endospermic. The endosperm is a bulky, starchy tissue that serves as the primary food storage tissue within the seed. It provides nourishment to the developing embryo during germination. The endosperm is often separated from the embryo by a proteinous layer known as the aleurone layer.
Embryo: The embryo in a monocotyledonous seed is relatively small compared to the endosperm. It consists of several parts:
- Cotyledon (Scutellum): Monocot seeds typically have a single cotyledon, which is large and shield-shaped. This cotyledon is known as the scutellum. While cotyledons in dicot seeds often serve as storage organs, in monocots, the primary function of the scutellum is the absorption of food from the endosperm and its transfer to the embryo.
- Axis: The embryo axis is the region connecting the cotyledon (scutellum) to the shoot and root portions. It includes the plumule (the shoot apex) and the radicle (embryonic root).
- Sheaths (Coleoptile and Coleorhiza): The plumule and radicle in monocot seeds are enclosed in protective sheaths. The plumule is protected by the coleoptile, which covers the shoot apex. The radicle is protected by the coleorhiza, which covers the embryonic root. These sheaths help the emerging seedling break through the soil surface during germination.

Monocotyledonous seeds have distinct features that differentiate them from dicotyledonous seeds, including the presence of a single cotyledon (scutellum) and the unique roles played by the endosperm, scutellum, and protective sheaths during germination.

Botanical Description of a Typical Flowering Plant – Mustard (Family: Brassicaceae)

Habit: The mustard plant is a herbaceous flowering plant with an annual habit, typically reaching a height of 1 to 2 meters.

Roots: The plant has a tap root system with lateral branches. The primary root is persistent and extends deep into the soil. Lateral roots are also present for anchorage and absorption.

Stem: The stem of the mustard plant is erect, cylindrical, and green. It becomes slightly woody as it matures. It is typically branched with nodes and internodes, bearing leaves and flowers.

Leaves: The leaves are simple, alternate, and exstipulate. They are sessile, with a leaf base directly attached to the stem. The lamina (leaf blade) is lanceolate, with serrated margins. The leaves are typically glabrous (without hairs) and arranged spirally along the stem.

Inflorescence: The mustard plant exhibits a racemose type of inflorescence. The main axis (peduncle) continues to elongate, and flowers are arranged along it in an acropetal succession.

Flower:

Calyx (K): The calyx consists of four sepals, which are united (gamosepalous). The calyx is often green, serving to protect the flower bud.
Corolla (C): The corolla consists of four petals, which are also united (gamopetalous). The petals are often yellow in color, and they serve to attract pollinators.
Androecium (A): The androecium consists of six stamens arranged in two whorls. The stamens are free (polyandrous), and each bears a bilobed anther with pollen sacs.
Gynoecium (G): The gynoecium consists of a single pistil, which is superior, indicating that the ovary is positioned above the attachment point of other floral parts. The pistil includes the ovary, style, and stigma.

Floral Formula: ⊕ Br K4 C4 A2+4 G(2)

⊕: Bisexual flower
Br: Bracteate (presence of bracts)
K4: Calyx with 4 united sepals
C4: Corolla with 4 united petals
A2+4: Androecium with 2 short stamens and 4 long stamens
G(2): Gynoecium with a superior ovary and 2 carpels

Floral Diagram: (The diagram represents the arrangement of floral parts in successive whorls, from outermost to innermost: Calyx, Corolla, Androecium, Gynoecium. The dot at the top indicates the position of the mother axis.)

Family: Solanaceae (Potato Family)

Vegetative Characters:

Plants: Members of this family include herbs, shrubs, and rarely small trees.
Stem: The stem can be herbaceous or woody. It is usually aerial, erect, cylindrical, and branched. The stem can be solid or hollow, and it may be either hairy or glabrous. In some cases, as seen in potatoes (Solanum tuberosum), there are underground stems used for food storage.
Leaves: Leaves are alternate and generally simple, although rare instances of pinnately compound leaves exist. They lack stipules and have reticulate venation.

Floral Characters:

Inflorescence: The inflorescence in Solanaceae can be solitary, axillary (arising from leaf axils), or cymose (cyclic) as observed in the genus Solanum.
Flowers: Solanaceae flowers are bisexual and exhibit actinomorphic symmetry (radial symmetry).
Calyx: The calyx consists of five sepals that are united. These sepals are persistent and show valvate aestivation (overlapping edges without any twisting).
Corolla: The corolla comprises five united petals with valvate aestivation.
Androecium: There are five stamens in the androecium, and they are epipetalous, meaning they are attached to the corolla.
Gynoecium: The gynoecium is bicarpellary (consisting of two carpels) and syncarpous (with fused carpels). The ovary is superior, bilocular (divided into two chambers), and has a swollen placenta bearing numerous ovules. The ovules are axile in position.

Fruits and Seeds:

Fruits: Solanaceae plants produce either berries or capsules as fruits.
Seeds: The seeds are numerous and endospermous, containing food reserves.

Floral Formula: ⊕

Economic Importance:

The Solanaceae family is of great economic importance. Many of its members serve as a source of food, such as tomatoes, brinjal (eggplant), and potatoes.
Some are used for spices, like chili peppers.
Medicinal plants within this family include belladonna and ashwagandha.
Tobacco, a member of Solanaceae, is widely used for smoking and fumigatory purposes.
Ornamental plants, such as petunias, also belong to this family.