Plus One Botany Notes Chapter 3 Morphology of Flowering Plants is part of Plus One Botany Notes. Here we have given Kerala Plus One Botany Notes Chapter 3 Morphology of Flowering Plants.
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|Chapter Name||Morphology of Flowering Plants|
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Kerala Plus One Botany Notes Chapter 3 Morphology of Flowering Plants
Plant morphology is the study of the physical form and external structure of plants. It is useful in the visual identification of plants.The angiosperm or flowering plants show a large diversity in external structure, they are all characterised by presence of roots, stems, leaves, flowers and fruits.
The plant body consists of a main axis, which may be branched or unbranched bearing lateral appendages. The main axis is divided into two parts.
- Root system
The underground part of the flowering plant is called the root system. Which develops from the radicle embryo and help in the fixation of the plant as well as absorption of water and minerals.
- Shoot system
The portion above the ground forms the shoot system. The aerial shoot system develops from the plumule embryo.
In plants, root is the non-green, cylindrical and descending part that grow downwards into the soil.
The root system can be of two types on the basis of place of origin.
1. Tape root system
ടേപ്പ് റൂട്ട് സിസ്റ്റം
The tap root develops from the radicle of embryo of a seed. In most of the plants, primary root persists and becomes stronger to form tap root. The first root forms by the elongation of radicle and is called primary root. It continuously grows and produces lateral roots called secondary roots. The further branches of the secondary roots are called teritiary roots and so on. These type of roots are present in dicots.
2. Fibrous root system
ഫിബ്രസ് റൂട്ട് സിസ്റ്റം
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 constitute the fibrous root system.
3. Adventitious roots system
In some plants, like grass, Monstera and the banyan tree, roots arise from parts of the plant other than the radicle and are called adventitious roots.
Functions of root
- Root provides fixation to the plants with soil.
- Root absorb water and minerals from the soil and provide it to all parts of the body.
- Roots of many plants store food for the use of other plant parts and for animals.
- Plants growing in waterlogged soil or marshy areas have special roots for respiration.
- Roots transport water and minerals in upward direction for the uses of stems and leaves.
Regions of the root
The root is covered at the apex by a thimble-like structure called the root cap. It protects the tender apex of the root as it makes its way through the soil.
A few millimetres above the root cap is the region of meristematic activity. The cells of this region are very small, thin-walled and with dense protoplasm. They divide repeatedly.
Region of elongation.
The cells proximal to the meristematic region undergo rapid elongation and enlargement and are responsible for the growth of the root in length. This region is called the region of elongation.
Region of maturation.
The cells of the elongation zone gradually differentiate and mature.Hence, this zone, proximal to region of elongation, is called the region of maturation.
From the region of maturation some of the epidermal cells form very fine and deli cate, thread-like structures called root hairs.These root hairs absorb water and minerals from the soil.
Modification Of root
1. For storage
Tap roots of some plants are modified for the storage of reserve food materials. Adventitious roots become tuberous in sweet potato. The tap root also modified for the storage function. They are conical, fusiform, napiform, tuberous,
e.g., radish, carrot, mirabilis, beet root and turnip.
2. For mechanical support
These are aerial roots which are produced from the main stem or branches penetrating into the soil and acting as pillars supporting the plant,
e.g., banyan tree.
These are small thick supporting roots growing obliquely from the basal nodes of the main stem. These provide mechanical support, e.g.. sugarcane, maize.
These roots are found in climbers. They are arise from the nodes, e.g., money plant.
These roots have chlorophyll and can synthesises food,
These roots occur in parasitic plant for absorbing nourishment from their host,
3. For respiration
These are special roots that develop in man grove plants (grow in marshy areas). The pneumatosphcres or aerophores or respiratory roots grow vertically upward and are negatively geotropic.
The stem is the ascending part of the axis bearing branches, leaves, flowers and fruits. It develops from the plumule of the embryo of a germinating seed. The stem bears nodes and internodes. The region of the stem where leaves are born are called nodes while inter-nodes are the portions between two nodes. The stem bears buds, which may be terminal or axillary. Stem is generally green when young and later often become woody and dark brown.
Functions of Stem
- It bears leaves, fruits, flowers and seed in position.
- It conducts water and minerals to roots, leaves, flower, fruits, etc.
- It holds flower in suitable position, so that pollination and fertilisation takes place.
- Many stems store food as reserve food materials.
- Some stems also help in photosynthesis and vegetative propagation.
- The underground stems help in perennation.
- Stem branches provide support to its various parts.
Modification Of Stem
1. Underground stem modifications
In some herbaceous plants, underground part of the stem stores food materials.
They are mainly four types.
- Rhizome, e.g., ginger, banana.
- Bulb, e.g., onion, garlic.
- Corm. e.g., amorphophallus, colocasia.
- Stem tuber, e.g., potato.
2. Sub-aerial stem modifications
In some weak stemmed plants, the weak stem and branches grow horizontally on the ground are called creepers. They are mainly of four types.
- Runners, e.g., oxalis, hydrocotyle.
- Suckers, e.g., chrysanthemum
- Stolon, e.g., jasmine.
- Offset, e.g., pistia, echhornial.
3. Aerial stem modifications
- Stem tendrils e.g.. passiflora, grape vine.
- Thorns e.g., citrus, canthlum.
- Phylloclade. e.g., cassurina, opuntia.
- Cladode. e.g.. asparagus.
The leaf is a lateral, generally flattened structure borne on the stem. It develops at the node and bears a bud in its axil. The axillary bud later develops into a branch. Leaves originate from shoot apical meristems and are arranged in an acropeta order. They are the most important vegetative organs for photosynthesis.
Parts of a leaf
Leaves also consists of two lateral outgrowths called stipules at their bases.
2. Leaf base.
The leaf is attached to the stern by the leaf base. In monocotyledons, the leaf base expands into a sheath covering the stem partially or wholly. In some leguminous plants the leaf base may become swollen, which, is called the pulvinus.
The petiole help hold the blade to light. Long thin flexible petioles allow leaf blades to flutter in wind, thereby cooling the leaf and bringing fresh air to leaf surface.
The lamina or the leaf blade is the green expanded part of the leaf with veins and veinlets. There is, usually, a middle prominent vein, which is 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 lamina varies in different leaves.
The arrangement of veins and the veinlets in the lamina of leaf is termed as venation.
In this type, the veins are repeatedly branched to form a network or reticulum,
e.g., dicot leaf
In this type, the veins run parallel to one another from the base to the apex or from the midrib to the margins,
e.g., monocot leaf
Types of leaves
Leaves are simple and compound.
1. Simple leaf
A leaf is said to be simple, when its lamina is entire or when incised, the incisions do not touch the midrib.
2. Compound leaf
When the incisions of the lamina reach up to the midrib breaking it into a number of leaflets, the leaf is called compound. A bud is present in the axil of petiole in both simple and compound leaves, but not in the axil of leaflets of the compound leaf.
The 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 palmately compound leaves, the leaflets are attached at a common point, i.e., at the tip of petiole, as in silk cotton.
Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. This is usually of three types.
A single leaf arises at each node, e.g., hibiscus, mustard, sunflower.
A pair of leaves arise at each node and lie opposite to each other,
e.g., calotropis, guava.
If more than two leaves arise at a node and form a whorl, it is called whorled.
e.g., alstonia, nerium.
Modification of leaves
1. Leaf tendrils.
These are thread-like sensitive structure, which can coil around a support to help the plant in climbing, e.g., wild pea, sweet pea. glory lily.
It is a green, short lived and flattened petiole or rachis of a leaf, which performs the function of photosynthesis.
e.g., australian acacia.
The segments of the leaf modify into bladder-like structure, which trap small insects present in the water.
It is a petiole modified into tendril to hold the pitcher upright. The leaf base is expanded to carry out photosynthesis. The leaf apex is modified into a lid. e.g., nepenthes, dischidia, sarracenia.
5. Leaf spines.
The entire leaf or a part of a leaf may be modified into a pointed structure called a spine.
These are thin, membranous leaves found at the nodal region. Each scale leaf contains an axillary bud in its axil.
The arrangement and distribution of flowers over a plant is called inflorescence. They can be three types.
1. Racemose inflorescence
In this type, the main axis continues to grow and the flowers are borne laterally in an acropetal succession (the older flowers are found towards the base and the younger ones at the apex) or centripetal (older towards periphery and younger towards centre).
2. Cymose inflorescence
In cymose inflorescene, the tip of the main axis terminates in a flower and further growth continues by one or more/lateral branches, which also behave like the main axis.
3. Special inflorescence
It mainly involved highly modified and densely crowded inflorescences
The flower is the reproductive unit in the angiosperms. It is meant for sexual reproduction. Morphologically, it is considered as a shoot bearing nodes and modified floral leaves. A flower is called modified shoot because the position of the buds of both flower and shoot which is same and can be in terminal or axillary in position.
Structure of a flower
ഒരു പൂവിന്റെ ഘടന
- A flower arises in the axil of a leaf like structure called bract. Flowers with bracts are called bracteate and those without bracts are called ebracteate.
- The terminal part of the axis of the flower is the receptable or thalamus. The receptable contains sepals, petals, stamens and carpels.
- If the leaves are present on the pedical, they are called bracteoles.
- Atypical flower consists of four distinct parts the calyx, the corolla, the androecium and the gynoecium. Calyx and corolla are accessory organs, while androecium and gynoecium are reproductive organs.
- In some flowers like lily, the calyx and corolla are not distinct and are termed as perianth.
- Bisexual flower
When a flower has both androecium and gynoecium.
- Unisexual flower
A flower having either only stamens or only carpels.
- Actinomorphic flower.
When a flower can be divided into two equal radial halves in any radial plane passing through the centre, it is said to be actinomorphic.
e.g., mustard, datura, chilli.
- Zygomorphic flower.
When it can be divided into two similar halves only in one particular vertical plane, it is zygomorphic.
e.g., pea, gulmohur, bean, cassia.
- Asymmetric flower.
A flower is asymmetric (irregular) if it cannot be divided into two similar halves by any vertical plane passing through the centre, as in canna.
- A flower may be trimerous, tetramerous or pentamerous when the floral appendages are in multiple of 3, 4 or 5, respectively.
- Flowers with bracts, reduced leaf found at the base of the pedicel, are called bracteate and those without bracts, ebracteate.
Types of flower
Based on the position of calyx, corolla and androecium in respect of the ovary on thalamus, the flowers are three types.
1. Hypogynous flower.
In this type flowers its gynoecium occupies the highest position while the other parts are situated below it. The ovary in such flowers is said to be superior.
e.g., mustard, china rose and brinjal.
2. Perigynous flower.
If gynoecium is situated in the centre and other parts of the flower are located on the rim of the thalamus almost at the same level, it is called perigynous. The ovary here is said to be half inferior.
e.g., plum, rose, peach.
3. Epigynous flower.
In this type, the margin of thalamus grows upward enclosing the ovary completely and getting fused with it, the other parts of flower arise above the ovary. Hence, the ovary is said to be inferior as in flowers of guava and cucumber, and the ray florets of sunflower.
Parts of flower
The calyx is the outermost whorl of the flower and the members are called sepals. Generally, sepals are green, leaf like and protect the flower in the bud stage. The calyx may be gamosepalous (sepals united) or polysepalous (sepals free).
2. Corolla (ago).
Corolla is composed of petals. Petals are usually brightly coloured to attract insects for pollination. Like calyx, corolia may be also free (gamopetalous) or united (polypetalous). The shape and colour of corolla vary greatly in plants. Corolla may be tubular, bellshaped, funnel-shaped or wheel-shaped.
It is coposed of stamens. When a stamens are attached to the petals, they are called epipetalous.
The stamen may be united into monodelphous. in two bundles, it is called diadelphous. in more than bundles, it is called polyadelphous.
Female reproductive part of the flower. It is made of carpels. Each carpel is formed of three parts, stigma, style and ovary. The swollen basal part is called ovary. Ovary containers ovules. The ovary is extended into tube like structure called style. The style terminates in stigma.
The mode of arrangement of sepals or petals in floral bud with respect to the other members of the same whorl is known as aestivation.
When sepals or petals in a whorl just touch one another at the margin, without overlapping. It is said to be valvaie. e.g., calotropis.
If one margin of the appendage overlaps that of the next one and so on it is called twisted.
e.g., china rose, lady’s finger and cotton.
If the margins of sepals or petals overlap one another but not in any particular direction this aestivation is called imbricate. e.g., cassia and gulmohur.
There are five petals, the largest (standard) overlaps the two lateral petals (wings) which in turn overlap the two smallest anterior petals (keel), this type of aestivation is known as vexillary or papilionaceous, e.g., pea and bean flowers.
The arrangement of ovules within the ovary is known as placentation. The placentation are of different types.
1. Marginal placentation.
Ovules are attached along the junction of two margins of the ovary wall. There is no true placenta. The ovary is one chambered, e.g., pea.
2. Axile placentation.
Ovules develop omthe central axis of the ovary. Ovary is multilocular.
e.g., lemon, tomato.
3. Parietal placentation.
The ovules develop on the inner wall of the ovary or on peripheral region,
e.g., cruciferas, argemone.
4. Basal placentation.
The placenta develops at the base of the ovary and bears a single ovule,
5. Free central placentation.
Ovules are develop on the central axis. Septa are absent. They have unilocular ovary,
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 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. They 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.
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 (as in wheat, maize) or two cotyledons (as in gram and pea).
Structure of dicotyledonous seed
The outermost covering of a seed is the seed coat. The seed coat has two layers, the outer testa and the inner tegmen. The hilum is a scar on the seed coat through which the developing seeds were attached to the fruit. Above the hilum is a small pore called the micropyle.
Structure of monocotyledonous Seed
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 endosperm separates the embryo by a proteinous layer called aleurone layer. The embryo is small and situated in a groove at one end of the endosperm.
Semi-technical description of a typical flowering plant
Various morphological features are used to describe a flowering plant. The description has to be brief, in a simple and scientific language and presented in a proper sequence. The plant is described beginning with its habit, vegetative characters – roots, stem and leaves and then floral characters inflorescence and flower parts.
The floral formula is the summerized account of the floral characters of a plant or a family represented by symbols.
Description of some important families
- This family was earlier called Papilonoideae,a subfamily of family Leguminosae. It is distributed all over the world e.g., gram, arhar, sem, moong, soyabean, groundnut, indigofera, sunhemp, Sesbania, Trifolium, lupin, sweet pea; muliathi.
- They are trees, shrubs, herbs. Root with root nodules, Stems are erect or climber, Leaves are alternate, pinnately compound or simple leaf base, pulvinate, stipulate, venation reticulate.
They are racemose, bisexual, zygomorphic, five sepals, gamoseffalous, imbricate aestivation, five petals, polypetalous, papilionaceous, consisting of a posterior standard, two lateral wings, two anterior ones forming a keel (enclosing stamens and pistil), vexillary aestivation. Androecium are ten, diadelphous, anther dithecous. Ovary superior, mono carpellary, unilocular with many ovules, style single, Fruits are legume, seeds are one to many, non-endospermic.
It is a large family, commonly called as the ‘potato family’. It is widely distributed in tropics, subtropics and even temperate zones. Plants mostly, herbs, shrubs and small trees Stems are herbaceous rarely woody, aerial stem areerect, cylindrical, branched, solid or hollow, hairy or glabrous, underground stem in potato. Leaves are alternate, simple, rarely pinnately compound, exstipulate and venation; reticulate.
Solitary, axillary or cymose as in Solanum, bisexual, actinomorphic, five sepals, united, persistent, valvate aestivation, petals are five, united and valvate aestivation. Androecium have five stamens, epipetalous. Gynoecium have bicarpeltary, syncarpous, ovary superior, bilocular, placenta, swollen with many ovules Fruits are berry or capsule. Seeds aremany, endospermous.
Commonly called the ‘Lily family’ is a characteristic representative of monocotyledonous plants. It is distributed world wide. They are perennial herbs with underground bulbs/ corms/ rhizomes. Leaves mostly basal, alternate, linear, exstipulate with parallel venation.
They aresolitary/cymose, often umbellate clusters. Flowers are bisexual, actinomorphic. Perianth tepal six (3+3), often united into tube, valvate aestivation. Six stamen(3+3), Gynoecium are tricarpellary, syncarpous, ovary superior, trilocular with many ovules, axile placenta- tion. Fruits are capsule, rarely berry. Seeds are endospermous.
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