Morphology of Flowering Plants | CBSE Class 11 Biology Notes

This note covers the morphology of flowering plants: the root and shoot systems, the types of roots and the regions of the root tip, the stem, the parts of a leaf, venation, simple and compound leaves, phyllotaxy, racemose and cymose inflorescences, the flower and its symmetry, the position of floral parts on the thalamus, the calyx, corolla and aestivation, the androecium and gynoecium, placentation, the fruit, dicotyledonous and monocotyledonous seeds, floral formulae and floral diagrams, and the family Solanaceae.

What makes up a flowering plant, and what kinds of root system are there?

The angiosperms show a large diversity in their external structure, or morphology. Even so, they are all characterised by the presence of roots, stems, leaves, flowers and fruits.

To classify or understand any higher plant, we need standard technical terms and definitions, and we need to know the variations in its parts that are adaptations to the environment: to various habitats, and for protection, climbing and storage.

Pull out any weed and you will see that it has roots, a stem and leaves, and it may be bearing flowers and fruits. The underground part of a flowering plant is the root system, while the portion above the ground forms the shoot system.

A whole plant is drawn in the soil, with brackets for the shoot system above the ground and the root system below. Labels mark the flower, fruit, stem, leaf, node, internode, bud, primary root and secondary root.

See Fig. 5.1 in your NCERT textbook

Tap, fibrous and adventitious roots

In the majority of dicotyledonous plants, the direct elongation of the radicle forms the primary root, which grows inside the soil. It bears lateral roots of several orders, referred to as secondary, tertiary and so on.

The primary root and its branches make up the tap root system, as seen in the mustard plant.

In monocotyledonous plants, the primary root is short-lived and is replaced by a large number of roots. These roots originate from the base of the stem and make up the fibrous root system, as seen in the wheat plant.

In some plants, such as grass, Monstera and the banyan tree, roots arise from parts of the plant other than the radicle. These are called adventitious roots. Generally, dicotyledonous plants have tap roots, while monocotyledonous plants have fibrous roots.

Three photographs: (a) a tap root, with the main root and its laterals labelled; (b) a dense tuft of fibrous roots; (c) adventitious roots growing out from thick stems.

See Fig. 5.2 in your NCERT textbook

What do roots do?

The main functions of the root system are:

• absorption of water and minerals from the soil;
• providing a proper anchorage to the plant parts;
• storing reserve food material;
• synthesis of plant growth regulators.

In some plants, the roots get modified for the storage of food, for mechanical support and for respiration.

What are the regions of the root tip?

A growing root tip shows distinct regions, one behind the other. Starting at the very tip and moving away from it, they are as follows.

1. Root cap: a thimble-like structure that covers the apex of the root. It protects the tender apex as the root makes its way through the soil.
2. Region of meristematic activity: a few millimetres above the root cap. Its cells are very small and thin-walled, with dense protoplasm, and they divide repeatedly.
3. Region of elongation: the cells proximal to the meristematic region undergo rapid elongation and enlargement. This region is responsible for the growth of the root in length.
4. Region of maturation: the zone proximal to the region of elongation. Here the cells of the elongation zone gradually differentiate and mature.

From the region of maturation, some of the epidermal cells form very fine and delicate, thread-like structures called root hairs. These root hairs absorb water and minerals from the soil.

A root tip is drawn with its apex at the bottom, covered by the root cap. Brackets mark, upwards from the cap, the regions of meristematic activity, elongation and maturation. Root hairs are drawn and labelled in the region of maturation.

See Fig. 5.3 in your NCERT textbook

What is a stem, and how can it be told apart from a root?

The stem is the ascending part of the axis that bears branches, leaves, flowers and fruits. It develops from the plumule of the embryo of a germinating seed.

The stem bears nodes and internodes. The nodes are the regions of the stem where leaves are borne, and the internodes are the portions between two nodes.

The stem bears buds, which may be terminal or axillary. A stem is generally green when young, and later it often becomes woody and dark brown.

Functions of the stem

The main function of the stem is spreading out branches that bear leaves, flowers and fruits. It conducts water, minerals and photosynthates.

Some stems also perform the functions of storage of food, support, protection and vegetative propagation.

Telling a stem from a root

Some morphological features of stems help to differentiate them from roots. These are the presence of nodes and internodes, the presence of multicellular hair, and a positively phototropic nature, meaning that the stem grows towards light.

What is a leaf, and what are its parts?

The leaf is a lateral, generally flattened structure borne on the stem. It develops at the node and bears a bud in its axil. This axillary bud later develops into a branch.

Leaves originate from the shoot apical meristems and are arranged in an acropetal order. A leaf is a lateral outgrowth of the stem that develops exogenously at the node.

Leaves are green in colour to perform the function of photosynthesis, and they are the most important vegetative organs for it.

The three main parts

A typical leaf consists of three main parts: the leaf base, the petiole and the lamina.

The leaf is attached to the stem by the leaf base, which may bear two lateral, small, leaf-like structures called stipules. In monocotyledons, the leaf base expands into a sheath that covers the stem partially or wholly.

In some leguminous plants, the leaf base may become swollen. This swollen leaf base is called the pulvinus.

The petiole helps hold the blade to light. Long, thin, flexible petioles allow leaf blades to flutter in the wind, which cools the leaf and brings fresh air to the leaf surface.

The lamina, or leaf blade, is the green, expanded part of the leaf, with veins and veinlets. There is usually a middle prominent vein, known as the midrib.

Veins provide rigidity to the leaf blade and act as channels of transport for water, minerals and food materials. The shape, margin, apex, surface and extent of incision of the lamina vary in different leaves.

Venation

Venation is the arrangement of the veins and veinlets in the lamina of a leaf. When the veinlets form a network, the venation is reticulate. When the veins run parallel to each other within a lamina, the venation is parallel.

Leaves of dicotyledonous plants generally possess reticulate venation, while parallel venation is characteristic of most monocotyledons.

(a) A leaf on a piece of stem, labelled lamina, stipule, petiole, leaf base and axillary bud. (b) A leaf whose veins form a network (reticulate). (c) A long, narrow leaf whose veins run side by side (parallel).

See Fig. 5.4 in your NCERT textbook

What are simple and compound leaves, and how are leaves arranged on a stem?

Simple and compound leaves

A leaf is simple when its lamina is entire or, when incised, the incisions do not touch the midrib.

When the incisions of the lamina reach up to the midrib and break it into a number of leaflets, the leaf is called compound.

A bud is present in the axil of the petiole in both simple and compound leaves, but not in the axil of the leaflets of a compound leaf.

Compound leaves may be of two types. In a pinnately compound leaf, a number of leaflets are present on a common axis, the rachis, which represents the midrib of the leaf, as in neem.

In a palmately compound leaf, the leaflets are attached at a common point, that is, at the tip of the petiole, as in silk cotton.

(a) Neem: many leaflets on both sides of a long axis labelled the rachis. (b) Silk cotton: several leaflets spreading from one point at the tip of a long petiole.

See Fig. 5.5 in your NCERT textbook

Phyllotaxy

Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. It is usually of three types: alternate, opposite and whorled.

Photographs of (a) a china rose twig with single leaves on alternate sides, (b) a guava twig with leaves in pairs, and (c) an Alstonia twig with several leaves spreading from one node.

See Fig. 5.6 in your NCERT textbook

What is an inflorescence, and how do racemose and cymose types differ?

A flower is a modified shoot. The change from a shoot tip to a flower takes place as follows.

1. The shoot apical meristem changes to a floral meristem.
2. The internodes do not elongate, and the axis gets condensed.
3. At successive nodes, the apex produces different kinds of floral appendages laterally, instead of leaves.
4. When a shoot tip transforms into a flower in this way, the flower is always solitary.

The arrangement of flowers on the floral axis is termed the inflorescence. Two major types are defined, depending on whether the apex develops into a flower or continues to grow: racemose and cymose.

Racemose inflorescence

In the racemose type, the main axis continues to grow, and the flowers are borne laterally in an acropetal succession, with the older flowers lower down and the younger flowers towards the apex.

Cymose inflorescence

In the cymose type, the main axis terminates in a flower, so it is limited in growth. The flowers are borne in a basipetal order, with the oldest flower at the tip of the axis.

Figure 5.7 is a photograph of a branch with many yellow flowers and buds on short stalks along a central axis. Figure 5.8 is a drawing in which the main axis ends in an open flower, and side branches below it bear further flowers and buds.

See Figs. 5.7 and 5.8 in your NCERT textbook

What is a flower, and how are flowers described?

The flower is the reproductive unit in the angiosperms, and it is meant for sexual reproduction.

A typical flower has four different kinds of whorls, arranged successively on the swollen end of the stalk, or pedicel. This swollen end is called the thalamus or receptacle. The four whorls are the calyx, corolla, androecium and gynoecium.

The calyx and corolla are accessory organs, while the androecium and gynoecium are reproductive organs.

In some flowers, such as lily, the calyx and corolla are not distinct, and they are termed the perianth.

Bisexual and unisexual flowers

When a flower has both androecium and gynoecium, it is bisexual. A flower having either only stamens or only carpels is unisexual.

Symmetry

In symmetry, a flower may be actinomorphic (radial symmetry) or zygomorphic (bilateral symmetry).

A flower that fits neither pattern, because it cannot be divided into two similar halves by any vertical plane passing through the centre, is asymmetric (irregular).

Number of parts and bracts

A flower may be trimerous, tetramerous or pentamerous when the floral appendages are in multiples of 3, 4 or 5 respectively.

A bract is a reduced leaf found at the base of the pedicel. Flowers with bracts are called bracteate, and those without bracts are ebracteate.

How are the floral parts placed on the thalamus?

Flowers are described as hypogynous, perigynous or epigynous. This depends on the position of the calyx, corolla and androecium with respect to the ovary on the thalamus.

Hypogynous flowers

In a hypogynous flower, the gynoecium occupies the highest position, and the other parts are situated below it. The ovary in such flowers is said to be superior, for example in mustard, china rose and brinjal.

Perigynous flowers

If the gynoecium is situated in the centre and the other parts of the flower are located on the rim of the thalamus, almost at the same level, the flower is perigynous. The ovary here is said to be half inferior, for example in plum, rose and peach.

Epigynous flowers

In epigynous flowers, the margin of the thalamus grows upward, enclosing the ovary completely and getting fused with it. The other parts of the flower arise above the ovary.

Hence the ovary is said to be inferior, as in the flowers of guava and cucumber, and in the ray florets of sunflower.

Four flowers in section. (a) Hypogynous: the ovary sits on top of the thalamus, with the other parts attached below it. (b) and (c) Perigynous: the ovary is in the centre of a cup-shaped thalamus, with the other parts on its rim. (d) Epigynous: the thalamus is fused around the ovary, and the other parts arise above it.

See Fig. 5.9 in your NCERT textbook

What are the calyx and corolla, and what is aestivation?

Each flower normally has four floral whorls: the calyx, corolla, androecium and gynoecium.

A whole flower labelled androecium, gynoecium, corolla, calyx and pedicel, and beside it the calyx, corolla, androecium and gynoecium drawn separately.

See Fig. 5.10 in your NCERT textbook

Calyx

The calyx is the outermost whorl of the flower, and its members are called sepals. Generally, sepals are green and leaf-like, and they protect the flower in the bud stage.

The calyx may be gamosepalous (sepals united) or polysepalous (sepals free).

Corolla

The corolla is composed of petals. Petals are usually brightly coloured to attract insects for pollination. Like the calyx, the corolla may be gamopetalous (petals united) or polypetalous (petals free).

The shape and colour of the corolla vary greatly in plants. The corolla may be tubular, bell-shaped, funnel-shaped or wheel-shaped.

Aestivation

Definition: Aestivation is the mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl.

The main types of aestivation are valvate, twisted, imbricate and vexillary.

Each column shows an outline of the petal arrangement above and a bud below it: (a) valvate, edges meeting without overlap; (b) twisted, each petal overlapping the next; (c) imbricate, overlapping in no regular direction; (d) vexillary, one large outer petal covering the others.

See Fig. 5.11 in your NCERT textbook

What are the androecium and the gynoecium?

Androecium

The androecium is composed of stamens. Each stamen represents the male reproductive organ and consists of a stalk, or filament, and an anther.

Each anther is usually bilobed, and each lobe has two chambers, the pollen-sacs. The pollen grains are produced in the pollen-sacs. A sterile stamen is called a staminode.

Stamens may be united with other members of the flower, such as the petals, or among themselves. The stamens in a flower may remain free, which is called polyandrous, or they may be united in varying degrees.

Gynoecium

The gynoecium is the female reproductive part of the flower and is made up of one or more carpels. A carpel consists of three parts:

• the ovary, the enlarged basal part;
• the style, the elongated tube that lies on the ovary and connects it to the stigma;
• the stigma, usually at the tip of the style, which is the receptive surface for pollen grains.

Each ovary bears one or more ovules attached to a flattened, cushion-like placenta.

When more than one carpel is present, the carpels may be free, as in lotus and rose, and are then called apocarpous. They are termed syncarpous when the carpels are fused, as in mustard and tomato.

After fertilisation, the ovules develop into seeds, and the ovary matures into a fruit.

What is placentation, and what are its types?

Definition: Placentation is the arrangement of ovules within the ovary.

Placentation is of different types, namely marginal, axile, parietal, basal, central and free central. Five of these are described below.

(a) Marginal: a pea pod with ovules along one edge. (b) Axile: a three-chambered ovary in section, with ovules at the centre where the walls meet. (c) Parietal: a one-chambered ovary with ovules on its inner wall. (d) Free central: ovules around a central axis, with no walls. (e) Basal: a single ovule at the base of the ovary.

See Fig. 5.12 in your NCERT textbook

What are fruits and seeds made of?

The fruit

The fruit is a characteristic feature of the flowering plants. It is a mature or ripened ovary, developed after fertilisation. If a fruit is formed without fertilisation of the ovary, it is called a parthenocarpic fruit.

Generally, the fruit consists of a wall, or pericarp, and seeds. The pericarp may be dry or fleshy.

When the pericarp is thick and fleshy, it is differentiated into the outer epicarp, the middle mesocarp and the inner endocarp.

In mango and coconut, the fruit is known as a drupe. These drupes develop from monocarpellary superior ovaries and are one-seeded.

In mango, the pericarp is well differentiated into an outer thin epicarp, a middle fleshy edible mesocarp and an inner stony hard endocarp. In coconut, which is also a drupe, the mesocarp is fibrous.

(a) A mango cut open, labelled epicarp, mesocarp, endocarp and seed. (b) A coconut split into two halves, showing its fibrous outer layer and white inner part.

See Fig. 5.13 in your NCERT textbook

Parts of a seed

The ovules, after fertilisation, develop into seeds. A seed is made up of a seed coat and an embryo.

The embryo is made up of a radicle, an embryonal axis and one or two cotyledons. There is one cotyledon in wheat and maize, and there are two in gram and pea.

The dicotyledonous seed

The outermost covering of a seed is the seed coat. It has two layers: the outer testa and the inner tegmen.

The hilum is a scar on the seed coat through which the developing seed was attached to the fruit. Above the hilum is a small pore called the micropyle.

Within the seed coat is the embryo, consisting of an embryonal axis and two cotyledons. The cotyledons are often fleshy and full of reserve food materials. The radicle and the plumule are present at the two ends of the embryonal axis.

In some seeds, such as castor, the endosperm formed as a result of double fertilisation is a food-storing tissue; such seeds are called endospermic seeds.

In plants such as bean, gram and pea, the endosperm is not present in mature seeds, and such seeds are called non-endospermous.

A whole seed labelled seed coat, hilum and micropyle, and beside it the opened seed, showing two cotyledons on a small embryonal axis with the plumule and radicle labelled.

See Fig. 5.14 in your NCERT textbook

The monocotyledonous seed

Generally, monocotyledonous seeds are endospermic, but some, as in orchids, are non-endospermic.

In the seeds of cereals such as maize, the seed coat is membranous and generally fused with the fruit wall. The endosperm is bulky and stores food.

The outer covering of the endosperm separates the embryo by a proteinous layer called the aleurone layer. The embryo is small and is situated in a groove at one end of the endosperm.

The embryo consists of one large, shield-shaped cotyledon known as the scutellum, and a short axis with a plumule and a radicle.

The plumule and radicle are enclosed in sheaths, called the coleoptile and coleorhiza respectively.

A small outline marks the endosperm and the embryo. The larger section labels the seed coat and fruit-wall, aleurone layer, endosperm, scutellum, coleoptile, plumule, radicle and coleorhiza.

See Fig. 5.15 in your NCERT textbook

How is a flowering plant described, and what are floral formulae and floral diagrams?

Various morphological features are used to describe a flowering plant. The semi-technical description has to be brief, in simple and scientific language, and presented in a proper sequence.

1. The habit of the plant is described first.
2. The vegetative characters follow: the roots, stem and leaves.
3. The floral characters come next: the inflorescence and the flower parts.
4. After the parts of the plant have been described, a floral diagram and a floral formula are presented.

Symbols in a floral formula

The floral formula is represented by symbols, as listed below.

Fusion is indicated by enclosing the figure within brackets. Adhesion is indicated by a line drawn above the symbols of the floral parts. The floral formula thus also shows cohesion and adhesion within parts of whorls and between whorls.

The floral diagram

A floral diagram provides information about the number of parts of a flower, their arrangement and the relation they have with one another. It is drawn in this way.

1. The position of the mother axis with respect to the flower is represented by a dot at the top of the diagram.
2. The calyx is drawn as the outermost whorl.
3. The corolla is drawn as the next whorl inside it.
4. The androecium is drawn as the whorl after the corolla.
5. The gynoecium is drawn in the centre.

The mustard flower

The floral diagram and floral formula shown below represent the mustard plant, of the family Brassicaceae. The floral formula is ⊕ ⚥ K₂₊₂ C₄ A₂₊₄ G̲₍₂₎.

Read symbol by symbol, it shows an actinomorphic, bisexual flower with 2 + 2 sepals, four petals, 2 + 4 stamens, and a superior ovary of two fused carpels.

A dot at the top marks the mother axis. Four sepals form the outer whorl, four petals lie inside them, then six stamens (two outer ones at the sides and four inner ones in pairs), and a two-chambered ovary sits in the centre. The floral formula is printed below.

See Fig. 5.16 in your NCERT textbook

What are the features of the family Solanaceae?

Solanaceae is a large family, commonly called the potato family. It is widely distributed in the tropics, the subtropics and even the temperate zones.

Its characters are listed below. In the family, the leaves are exstipulate and the fruit is a berry or capsule; potato (Solanum tuberosum) has an underground stem.

The floral formula of Solanaceae is ⊕ ⚥ K₍₅₎ C₍₅₎ A₅ G̲₍₂₎, with a curved line drawn above C₍₅₎ and A₅.

It shows an actinomorphic, bisexual flower with five united sepals, five united petals and five stamens. The line above C and A shows the adhesion of stamens to petals, and G̲₍₂₎ shows a superior ovary of two fused carpels.

(a) A flowering twig with simple leaves, white star-shaped flowers and clusters of small red fruits. (b) A flower. (c) L.S. of the flower. (d) Stamens. (e) Carpel. (f) Floral diagram with a five-sided calyx, five petals, five stamens and a central ovary with many ovules.

See Fig. 5.17 in your NCERT textbook

Economic importance

Many plants of this family are useful to people.

Glossary

• Tap root system — the primary root, formed by direct elongation of the radicle, together with its lateral roots of several orders, as in mustard.
• Adventitious roots — roots that arise from parts of the plant other than the radicle, as in grass, Monstera and the banyan tree.
• Rachis — the common axis bearing the leaflets of a pinnately compound leaf; it represents the midrib, as in neem.
• Phyllotaxy — the pattern of arrangement of leaves on a stem or branch, usually alternate, opposite or whorled.
• Inflorescence — the arrangement of flowers on the floral axis; its two major types are racemose and cymose.
• Thalamus — the swollen end of the stalk or pedicel of a flower, also called the receptacle, on which the floral whorls are arranged.
• Perianth — the term used for the calyx and corolla together when they are not distinct, as in lily.
• Aestivation — the mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl.
• Placentation — the arrangement of ovules within the ovary, for example marginal, axile, parietal, free central or basal.
• Parthenocarpic fruit — a fruit that is formed without fertilisation of the ovary.
• Scutellum — the one large, shield-shaped cotyledon of the embryo in a cereal seed such as maize.

Common errors and misconceptions

• Misconception: A compound leaf has a bud in the axil of each leaflet. Correct: A bud is present in the axil of the petiole of both simple and compound leaves, but not in the axil of the leaflets of a compound leaf.
• Misconception: In a racemose inflorescence the main axis ends in a flower. Correct: In racemose inflorescences the main axis continues to grow and the flowers are borne laterally in acropetal succession. The cymose axis is the one that ends in a flower.
• Misconception: A perigynous flower has an inferior ovary. Correct: The ovary is half inferior in a perigynous flower such as plum. It is inferior in an epigynous flower such as guava, and superior in a hypogynous flower such as mustard.
• Misconception: The fruit develops from the ovules. Correct: After fertilisation, the ovary matures into the fruit and the ovules develop into seeds. A parthenocarpic fruit forms without fertilisation of the ovary.
• Misconception: All monocotyledonous seeds are endospermic. Correct: Monocotyledonous seeds are generally endospermic, but some, as in orchids, are non-endospermic. Among dicotyledons, castor seeds are endospermic, while bean, gram and pea seeds are not.
• Misconception: Epipetalous and epiphyllous stamens are the same thing. Correct: Epipetalous stamens are attached to the petals, as in brinjal. Epiphyllous stamens are attached to the perianth, as in lily.
• Misconception: Twisted and imbricate aestivation are the same, since margins overlap in both. Correct: In twisted aestivation one margin overlaps the next and so on, as in china rose. In imbricate aestivation the margins overlap in no particular direction, as in Cassia.

Exam-style questions with model answers

Q1. How is a pinnately compound leaf different from a palmately compound leaf? Give one example of each. [2 marks]

1. In a pinnately compound leaf, a number of leaflets are present on a common axis, the rachis, which represents the midrib of the leaf. Example: neem.
2. In a palmately compound leaf, the leaflets are attached at a common point, the tip of the petiole. Example: silk cotton.

Q2. Explain, with suitable examples, the different types of phyllotaxy. [3 marks]

1. Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. It is usually of three types.
2. Alternate: a single leaf arises at each node in an alternate manner, as in china rose, mustard and sunflower.
3. Opposite: a pair of leaves arises at each node, and the two lie opposite each other, as in Calotropis and guava.
4. Whorled: more than two leaves arise at a node and form a whorl, as in Alstonia.

Q3. Differentiate between racemose and cymose inflorescences. [3 marks]

1. The two types are distinguished by whether the apex develops into a flower or continues to grow.
2. Racemose: the main axis continues to grow, and the flowers are borne laterally in an acropetal succession.
3. Cymose: the main axis terminates in a flower and is therefore limited in growth; the flowers are borne in a basipetal order.

Q4. What is aestivation? Describe its main types with examples. [4 marks]

1. Aestivation is the mode of arrangement of sepals or petals in the floral bud with respect to the other members of the same whorl.
2. Valvate: the sepals or petals just touch one another at the margin, without overlapping, as in Calotropis.
3. Twisted: one margin of each appendage overlaps that of the next one, and so on, as in china rose, lady's finger and cotton.
4. Imbricate: the margins overlap one another but not in any particular direction, as in Cassia and gulmohur.
5. Vexillary or papilionaceous: in pea and bean, the largest of the five petals (standard) overlaps the two lateral petals (wings), which in turn overlap the two smallest anterior petals (keel).

Q5. Describe the various types of placentation found in flowering plants, with examples. [5 marks]

1. Placentation is the arrangement of ovules within the ovary.
2. Marginal: the placenta forms a ridge along the ventral suture of the ovary, and the ovules are borne on this ridge in two rows, as in pea.
3. Axile: the placenta is axial, and the ovules are attached to it in a multilocular ovary, as in china rose, tomato and lemon.
4. Parietal: the ovules develop on the inner wall of the ovary or on its peripheral part. The ovary is one-chambered but becomes two-chambered due to a false septum, as in mustard and Argemone.
5. Free central: the ovules are borne on a central axis and septa are absent, as in Dianthus and primrose.
6. Basal: the placenta develops at the base of the ovary, and a single ovule is attached to it, as in sunflower and marigold.

Q6. Describe the structure of a monocotyledonous seed such as maize. [5 marks]

1. Monocotyledonous seeds are generally endospermic, though some, as in orchids, are non-endospermic.
2. In cereals such as maize, the seed coat is membranous and generally fused with the fruit wall.
3. The endosperm is bulky and stores food. A proteinous layer, the aleurone layer, at the outer covering of the endosperm separates the embryo.
4. The embryo is small and lies in a groove at one end of the endosperm.
5. It consists of one large, shield-shaped cotyledon, the scutellum, and a short axis bearing a plumule and a radicle.
6. The plumule is enclosed in a sheath called the coleoptile, and the radicle in a sheath called the coleorhiza.

Q7. Give the floral characters and the floral formula of the family Solanaceae, and name two of its economically important plants. [5 marks]

1. Inflorescence: solitary, axillary or cymose, as in Solanum.
2. Flower: bisexual and actinomorphic.
3. Calyx: five sepals, united and persistent, with valvate aestivation.
4. Corolla: five petals, united, with valvate aestivation.
5. Androecium: five stamens, epipetalous.
6. Gynoecium: bicarpellary, obliquely placed and syncarpous; the ovary is superior and bilocular, with a swollen placenta bearing many ovules, and axile placentation.
7. Fruit: berry or capsule. Seeds: many and endospermous.
8. Floral formula: ⊕ ⚥ K₍₅₎ C₍₅₎ A₅ G̲₍₂₎, with a line above C₍₅₎ and A₅ to show that the stamens adhere to the petals.
9. Economic importance: tomato and potato are food plants, and tobacco is a fumigatory.

Key takeaways

• Flowering plants have a root system below the ground and a shoot system above it. Generally, dicotyledons have a tap root system and monocotyledons have a fibrous root system.
• A root tip has a root cap, then regions of meristematic activity, elongation and maturation. Root hairs from the maturation region absorb water and minerals.
• The stem develops from the plumule and bears nodes, internodes and buds. Nodes and internodes, multicellular hair and a positively phototropic nature help to differentiate stems from roots.
• In racemose inflorescences the main axis keeps growing and flowers are acropetal; in cymose inflorescences the axis ends in a flower and flowers are basipetal.
• The ovary is superior in hypogynous flowers, half inferior in perigynous flowers and inferior in epigynous flowers.
• After fertilisation the ovary becomes the fruit and the ovules become seeds; mango and coconut are drupes from monocarpellary superior ovaries.
• A floral formula uses symbols such as ⊕, K, C, A and G; brackets show fusion and a line above shows adhesion, as in the Solanaceae formula.

Test yourself

What are adventitious roots? Name two plants that have them.

Adventitious roots arise from parts of the plant other than the radicle. Grass, Monstera and the banyan tree have them.

Which region of the root tip is responsible for growth in length?

The region of elongation, where the cells proximal to the meristematic region undergo rapid elongation and enlargement.

Give one example each of actinomorphic, zygomorphic and asymmetric flowers.

Mustard is actinomorphic, pea is zygomorphic, and canna is asymmetric. Datura and chilli are also actinomorphic, while gulmohur, bean and Cassia are zygomorphic.

What makes the ovary of mustard two-chambered?

Mustard has parietal placentation. Its ovary is one-chambered but becomes two-chambered due to the formation of a false septum.

Name the three layers of a thick, fleshy pericarp and say which part of mango is eaten.

The outer epicarp, middle mesocarp and inner endocarp. In mango, the middle fleshy mesocarp is the edible part, and the endocarp is stony and hard.

What are the coleoptile and the coleorhiza?

They are sheaths in the embryo of a monocotyledonous seed such as maize. The coleoptile encloses the plumule, and the coleorhiza encloses the radicle.