MORPHOLOGY OF FLOWERING PLANTS

MORPHOLOGY OF FLOWERING PLANTS:

Introduction:

Ø  Plant morphology or phytomorphology is the study of physical form and external structure of plants.

Ø  Morphology is the study of various external features of an organism. They are all characterized by presence of roots, stems, leaves, flowers and fruits.

ROOT

Introduction:

Ø  Root is underground part of the plant and develops from the elongation of radical of the embryo by germinating of seeds.

Ø  Roots are negatively phototrophic i.e. it grows away from sunlight and positively geotrophic i.e. grows towards the earth. Geotrophism means the directional growth of plant in response to gravity.

Ø  In dicot plants, direct elongation of the radicle leads to the formation of primary root which grows inside the soil. It bears lateral roots of several orders that are referred to as secondary, tertiary roots.

Types of Roots:

Roots are classified into three categories:

1.       Tap Root

2.       Fibrous Root

3.       Adventitious Root

1.       TAP ROOT:

·         It is originated from radicle.

·         Tap roots are persistent in dicot plants.

·         Direct elongation of radicle results in formation of primary root. Primary roots brings secondary and tertiary roots.

·         Primary root along with its branches makes the tap root system.

·         Eg: Mustard, banyan, Gram, Pea, Mango.

2.       Fibrous Root:

·         It is originated from the base of stem.

·         Here large number of roots replaced the primary roots.

·         This type of root found in monocot plant.

·         Primary root is short lived after germination. This is replaced by large number of roots and all of these emerge from .the base of stem.

·         Eg: Paddy grass

 

3.       Adventitious Root:

·         Roots are developed from any part of the plant other than radicle.

·         These roots are used for various purposes like mechanical support and vegetative propagation.

·         Eg: Monstera and Banyan tree.

Region of Root:

These are following regions of roots that are present along the roots:

        I.            Root Cap: It covered the apex by thimble like structure which protects the tender apical part.

      II.            Region of Meristmatic activity:

Ø  Cells of this region have the capability to divide. So these cells are known as meristmatic cells.

Ø  This region is small, thin walled and with dense protoplasm.

    III.            Region of Elongation:

Ø  This is an elongated and enlarged region which lies few millimeters above the root cap.

Ø  These cells are responsible for the growth of root in length.

    IV.            Region of Maturation:

Ø  This region has differentiated into matured cells.

Ø  Some of the epidermal cells of this region form thread like root hairs which absorbs water and nutrients from the soil.

Modifications of Root:

Roots are modified for support, storage of food etc.

For support:

        I.            Prop Roots: These roots are modified for support in banyan tree.

      II.            Stilt Roots: These roots are also modified for support like in maize and sugarcane.

    III.            Pneumatophores: These roots are also known as respiratory roots because these roots are involved in respiration like in Rhizophora (mangroves).

For storage of food:

        I.            Fusiform: In radish roots are involve for storage purposes.

      II.            Napiform: In turnip these roots are used for storage purpose.

    III.            Conical:  Present in Carrot.

Function of Roots:

Ø  Absorption of water and minerals from soil.

Ø  Helps in anchorage or attachment of the plant body.

Ø  It stores reserve food material.

Ø  It helps in synthesis of plant growth regulators.

 

STEM:

Introduction:

Ø  Stem is the ascending part of the plant formed by the elongation of embryo.

Ø  It is the aerial part of the plant develops from the plumule of embryo.

Ø  It bears nodes and internodes. Nodes are the points on stem from where buds, leaves and branching twigs originate. Internodes are the sections of stem between nodes.

Ø  Stem is positively phototrophic; it means it grows towards the direction of sunlight and negatively geotrophic i.e. grows away from earth.

Ø  Stem bears bud which may be axillary or terminal.

Ø  Most stems are found above ground but some of them grow underground as in potato.

Ø  Stem can be either unbranched or highly branched.

Ø  Petiole is a stalk that extends from stem to the base of leaf.

Ø  Living cells in stems get their oxygen supply of oxygen from the air through pores called stomata and lenticels in their epidermis.

Modification of Stem:

Stems are modified to perform following functions:

1.       For food Storage: These parts of respective plants are modified for food storage.

Eg: Rhizome in Ginger, Tuber in potatoe, Bulb in onion, Corm and colocasia. 

2.       For Support: Such parts of the plants are modified to support plant.

Eg: Stem tendrils of watermelon, Grapewine and cucumber.

3.       For Protection: These parts are modified to protect plant from external environment.

Eg: Axillary buds of stem of citrus, Bougainvillea get modified into pointed thorns which protect the plant from browsing animals.

4.       For Vegetative propagation:

Eg: Underground stem of grass, strawberry and lateral branches of mint and jasmine.

5.       For Assimilation of food: Some parts of plants are modified to synthesize food.

Eg: Flattened stem of opuntia contains chlorophyll which synthesizes glucose by photosynthesis process.

 

Functions of Stem:

Ø  Stem helps in transport of water, minerals and sugars to different parts of the plant.

Ø  Stem also help in synthesis of food by the process of photosynthesis.

Ø  Stem support and hold leaves, flowers and fruits.

Ø  It helps in storage of food produces during the process of photosynthesis.

Ø  Stem bears flowers and fruits in position to facilitate the process of pollination and fertilization.

Ø  Secondary function of stem are perennation, vegetative propagation or as climbers.

Ø  Allows the conduction of water from the soil to leaves and food from leaves to oyher prts of plant.

Ø  It provides sufficient space between leaves, so that they receive sufficient air and sunlight.

 

 

LEAF:

Introduction:

·         Leaf is a lateral and flattened green structure.

·         It develops exogenously at the node and bears a bud in its axil which is known as axillary bud which later develops into branch.

·         Leaves are originated from shoot apical meristem.

·         Leaves are arranged in an acropetal manner. It means older leaves are found at the base of branch while newer leaves are borne towards the tip of branch.

·         Leaves are the most important vegetative organ for photosynthesis.

Parts of leaf:

Leaf is divided into three parts:

1.       Leaf Base: Leaf is attached to the stem by the leaf base and may bear two lateral small leaves like structure called stipules. In monocot, the leaf base expands into sheath covering the stem particularly known as sheathing leaf base. In some leguminous plants, the leaf base may become swollen known as pulvinous leaf base.

2.       Petiole: It helps in holding the blade to light, long thin flexible petioles allow leaf blade to flatter in wind, thereby cooling the leaf and bringing fresh air to leaf surface.

3.       Lamina: Leaf base is the green expanded part of the leaf with veins and veinlets. There is usually a middle prominent vein which is called as midrib. Veins provides rigidity to the leaf blade and act as channels of transport for water, minerals and food material.

Venation:                             

Ø  Arrangement of veins and veinlets in the lamina of leaf called as venation.

Ø  Venation can be categorized into two types:

                   I. When veinlets form a network, it is called as reticulate venation. Eg:  Dicot

                   II. When veins run parallel to each other within a lamina is called parallel venation.

 Eg: Monocot

Types of Leaf:

Leaves are divided into two types:

        I.            Simple leaf: When lamina of leaf is entire or when incised, the incisors do not touch the midrib.

      II.            Compound leaf: When incisors of the lamina node up to the midrib breaking it into a number of leaflets, the leaf is called compound leaf. It is divided into two types:

Ø  Pinnately compound leaf: In this type number of leaflets is present on a common axis which is known as rachis, which represents the midrib of the leaf. Eg:

Ø  Palmately compound leaf: The leaflets are attached at a common point i.e. at the tip of petiole. Eg: Silk cotton

Phyllotaxy:

Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. It is basically of three types:

1.       Alternate phyllotaxy: A single leaf arises at each node in n alternate manner.

Eg: Chin rose, Mustard, Sunflower.

2.       Opposite phyllotaxy: In this type of phyllotaxy a single leaf arises at each node and lie opposite of each other. Eg: Calotropis and Guava.

3.       Whorled phyllotaxy: If more than two leaves arises at a node and form a whorl.

 Eg: Alstania

Infloroscence:

Arrangement of flowers on the floral axis is called as inflorescence. Depending on whether the apex gets converted into flower or continuosly to grow, two major types of inflorescence are there:

1)      Racemose inflorescence:

·         In this form main axis continues to grow; the flowers are borne laterally in an acropetal manner.

·         Here younger leaves are present at the tip while older flowers are arranged at the base. Such arrangement is called as acropetal succession.

2)      Cymose inflorescence:

·         Here main axis terminates in a flower, a limited growth is found.

·         Flowers are borne in basipetal manner.

·         Younger flowers are present at the base of inflorescence, while opposite flowers are present at the  . Such arrangement is called as basipetal arrangement.

Modification of leaf:

Leaves are modified to support following functions:

        I.            For storage purposes: Leaves are modified to store food. Eg: fleshy leaves of onion and garlic.

      II.            For support: Leaves are modified into tendrils for climbing purposes. Eg: Peas.

    III.            For defence:  Leaves are converted into spines. Eg: Cactus.

    IV.            For photosynthesis: In some plants, the leaves are small and short lived. The petioles in these plants expand, become green and synthesize food by photosynthesis process.                             Eg: Australium acacia

      V.            For insectivory: Some leaves of plants are get modified to trap insects as their prey and they becomes predator. Eg: Pitcher plant, venus fly trap.

 

FLOWER

Introduction:

Ø  A reproductive unit in angiosperm which is meant for sexual reproduction.

Ø  A typical flower has four different kinds of whorls arranged successively on the swollen end of the stalk or pedicle called as thalamus or receptacle.

Ø  Flowers are categorized into two forms:

Accessory organs

Reproductive organs

a)      Accessory organs: Those organs which are not participated in reproductive function. They are essential for attracting insects for pollination. These include calyx and corolla.

b)      Reproductive organ: They are essential for the continuity of generation. It includes androecium and gynoecium.

Perianth: Those flowers in which calyx and corolla are not distinct are termed as perianth.  Eg; Lily

        I.            Calyx (Sepals):  It represents the outermost whorl of flower. Sepals of flower considered as group which is called calyx. Sepal is one of the individual leaves or parts of calyx of flower. There are two cases are found:

Ø  Gamosepalous: When sepals are united then it known as gamosepalous.

Ø  Polysepalous: When sepals are free, then it is known as polysepalous.

      II.            Corolla (Petals): Petals are brightly colored structures to attract insects for pollination. Shape and color vary greatly in plants. Corolla may be tubular, bell shaped funnel shaped or wheel shaped.

    III.            Androecium (Stamen): It represents male reproductive organ. It consists of stalk or filament and an anther. Each anther is usually bilobed and each lobe has two chambers (pollen sacs). Pollen grains are produced in pollen sacs. Pollen grains are produced in pollen sacs. Sterile stamen is called staminode

When stamen attached to petals, it is called epipetalous. Eg: Brinjal     

When stamens are attached to the perianth, they are called epiphyllous. Eg; Lily  

When stamens are free this condition is known as polyandrous.      

When stamens are bound in one bunch or bundle, it is known as monoadelphous.

Eg: China rose

When stamens are present in two bundles, they are called as diadelphous.  Eg: Pea                                                                                                                                                                                                                                                                 

    IV.            Gynoecium (Carpel):  It is the female reproductive part of the flower. It is made up of one or more carpel. Carpel consists of a stigma, a style and an ovary. Stigma is located at the tip of style; stigma is the receptive surface of the pollen grains. Style is an elongated tube which connect the ovary to the stigma and ovary is enlarged basal part. Each ovary bears one or more ovule attached to a flattened cushion like placenta.

      V.            Ovary is of two types: When more than one carpel is present, they may be free, so it is known as apocarpous. Eg : Lotus, rose. When carpels are fused, they are known as syncarpous.                     

Eg: Mustard and tomato

    VI.            After fertilization ovules develop into seeds and ovary matures into a fruit.

 

FRUIT:

Introduction:

It is a mature or ripened ovary developed after fertilization. If a fruit is formed without fertilization of the ovary, it is called as parthenocarpic fruit. Fruit consists of a wall or pericarp of seeds. Pericarp may be dry or fleshy. Pericarp includes three layers: Epicarp which is the outermost layer, Mesocarp, the middle one and endocarp i.e. inner, thick and fleshy.

Eg: Mango and Coconut develop from monocarpellary superior ovaries and are one seeded. In mango, pericarp is well differentiated into an outer thin epicarp, middle fleshy edible mesocarp and inner stony and hard endocarp. In coconut mesocarp is fibrous.

Fruit is the seed bearing structure in angiosperm formed from ovary after fertilization.

SEED

Ø  Seed is a propagating organ formed in the sexual reproductive cycle of angiosperm and gymnosperm.

Ø  After fertilization ovules, develop into seed. It consists of seed coat and an embryo.

Ø  The embryo consists of radicle, an embryonal axis and one or two cotyledons

Ø  Outermost covering of seed is called seed coat. Seed coat is further subdivided into outer testa and inner tegmen. Within seed coat is embryo consists of an embryonal axis and two cotyledons.

Ø  The cotyledons are often fleshy and full of reserve food material.

Ø  In plants such as bean, gram and pea, the endosperm is not present in mature seeds.

Ø  Monocots seeds are endospermic but some as in orchids are non-endospermic. Endosperm is bulky and stores reserve food material.

Ø  Outer covering of endosperm separates the embryo by a  proteinaceous layer called aleuronic layer.

Ø  Embryo is small and situated in a groove at one end of the endosperm. It consists of one long and shield shaped cotyledons.

 

 

 

 

 

 

Placentation:

The arrangement of ovules within the ovary is known as placentation. It is of following types:

1.       Marginal: In this type, the placenta forms a ridge along the ventral suture of the ovary and ovules are borne on this ridge forming two rows. Eg: Pea

2.       Axile: Ovules are attached to it in multilocular ovary. Eg: China rose, tomato, lemon

3.       Parietal: Ovules develop on the inner wall of the ovary or on peripheral part. Ovary is one chambered but it becomes two chambered due to the formation of the false septum. Eg: Mustard and Argemone.

4.       Free central: When the ovules are borne on the central axis and septa are absent. Eg: Dianthus and Primrose.

5.       Basal: Placenta develops at the base of ovary and a single ovule is attached to it.

Eg: Sunflower, marigold.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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