Anatomy Of Flowering Plants

Anatomy Of Flowering Plants

INTRODUCTION

  • The study of internal structures of organisms is called anatomy.
  • It includes the study of the type of cells present in the body: whether eukaryotic or prokaryotic, an approximate number of cells in the body.
  • the tissues are organised into organs, etc.
  • It also shows the various adaptations of the plants to survive in different environments.

TISSUE.

  • As the cells group together, they form tissues. Different tissues arise as a result of interactions among the constituent cells.
  • Properties of tissues are not present in the constituent cells.
  • These cells usually perform a common function, however, they may be structurally similar or dissimilar to one another.
  • Hence, a tissue can be defined as a group of structurally similar or dissimilar cells that perform a common function and have a common origin.
  • A plant is made up of different kinds of tissues.
  • meristematic tissue is a group of immature cells that are preparing to divide or are in continuous state or division.

 

MERISTEMS

  • Meristems are the specialised areas in the plant body that possess the meristematic tissue.
  • These are the areas of active cell division as the cells present in them keep on dividing to term other cells.

Classification of Meristems

The meristems can be divided on the basis of

  • Origin or order of appearance in the life of a plant. Their position in the body of a plant.
  • On the basis of origin in life of a plant : On this basis, the meristems can be distinguished into
  • Primary meristems : The meristematic cells that appear early in the life of a plant and contribute to the formation of primary plant body are called primary meristems.
  • Secondary meristems : The meristems that appear later than primary meristems in life of a plant and are responsible for producing the secondary tissues, particularly the woody areas, are called secondary meristems.

Anatomy Of Flowering Plants

On the basis of position in the plant body

The meristems occupy different areas in the body of plants and depending upon this, they can be divided into:

  • Apical meristem : As the name signifies, these tissues are found at the apices or tips of stem, root or branch.

Function of apical meristem :

  • The apical meristems produce the primary tissues of plant body and are responsible for the primary growth of the plants.
  • They principally contribute to increase in the length, i.e., elongation of the plants along their axis.

Formation of axillary bud

  • Plant bud is an undeveloped or underdeveloped shoot.
  • the cells of shoot apical meristem continuously divide to increase their number to elongate the stem.

Intercalary meristem

  • these meristems are intercalated in between the mature tissues, i.e., the permanent tissues.
  • Hence these meristems are separated from the apex of the organ by mature tissue.

Lateral meristem :

  • These meristems are present along the lateral sides of roots and shoots of many plants. They are found in the mature regions of roots and shoots.
  • The lateral meristems are the cylindrical meristems which divide in the radial direction resulting in the increase in girth of the stems and roots.
  • Lateral meristems are responsible for producing the secondary tissues like secondary xylem, secondary phloem, secondary medullary rays, cork, secondary cortex etc.

Permanent Tissues

Till now we have studied that the cells of primary and secondary meristems undergo division and different to produce primary and secondary permanent tissues of the plant body respectively.

Classification of permanent tissues :

  • Permanent tissues are basically of two types
  • Simple permanent tissues: A tissue is said to be simple when it is made up of only one type of cells.
  • Various simple tissues are found in plants which make up the body of plants. These are
  • Parenchyma
  • Collenchyma
  • Sclerenchyma
  • Parenchyma: The various features of parenchyma is Aerenchyma: Aarenche bodies. This is specula air cavities are filled with and it facilitates the
  • This tissue forms the major component within various organs of plants and is present in all of them, i.e., roots, stems, leaves, flowers, fruits and seeds.
  • It forms the main bulk of the plant body.
  • Functions of Parenchyma: Parenchyma performs various functions like:
  • Storage of food: One of the main function of this tissue is the storage of food. The parenchymatous cells store various food materials like carbohydrates, oils, fats, proteins, etc.
  • Photosynthesis: Some parenchymatous cells develop chloroplasts in them and perform, i.e., synthesis of food from inorganic substances in the presence of light energy. Chloroplasts containing parenchyma is called the chlorenchyma.
  • Secretion: Some parenchymatous cells secrete substances like resin, nectar, oil, etc.
  • Collenchyma: Various features of collenchyma are as follows:
  • Collenchyma is an elastic, living, mechanical tissue.
  • Cells of this tissue are called collenchymatous cells which may be oval, spherical or polygonal in shape.
  • The intercellular spaces are absent because these cells are closely packed with each other.
  • The collenchyma occurs in layers below the epidermis in dicotyledonous plants.
  • Collenchyma usually occurs in the form of 3-4 layers below the epidermis in dicotyledonous plants.
  • It is found either as homogeneous, i.e., continuous layer or in the form of patches discontinuously.

Types of complex tissue : Two types of complex tissues are found in the plants.

(1) Phloem

(2) Xylem : It is the chief water-conducting tissue of the plants. Xylem functions as a conducting tissue for water and minerals from the roots to the top of plants, i.e., to the stems and leaves.

Types of xylem : On the basis of origin, xylem tissue can be (a) primary xylem, (b) secondary xylem.

Primary xylem :

  • The xylem which arises early, 1.e., during primary growth of plant body is called primary xylem.
  • It is further of two types on the basis of origin.
  • Protoxylem, (2) Metaxylem.
  • The first formed primary xylem is called protoxylem and the later formed primary xylem is called metaxylem.

Secondary xylem: Secondary xylem is the xylem that is formed during secondary growth.

It is formed by the vascular cambial ring.

Elements of xylem :

  • Xylem is a complex tissue which is composed of following four different kinds of elements.
  • Tracheid’s, B. Vessels, C. Xylem fibres, D. Xylem parenchyma.

Tracheid

Structure : Tracheid are the elongated cells with tapering ends. These

are the tube-like cells (one tube is one cell) whose both ends taper slowly to give an appearance of pointed ends.

  • The tracheids have thick and lignified walls (having a deposition of lignin in the cell walls).
  • These are the dead cells and are without protoplasm.

Occurrence: Tracheids are found in all categories of vascular plants, i.e., Pteridophytes,

Gymnosperms and Angiosperms (flowering plants).

Functions :

  • Main purpose of tracheids is to transport water and minerals from roots to stems and leaves.
  • Due to the presence of thickened and hard wall, they also provide the mechanical support to the plant body.

Xylem fibres :

  • They are the sclerenchymatous fibrous They are long, narrow and lapering at its ends They are also the dead elements of vessels and tracheids
  • They have highly thickened lignified walls.
  • Xylem fibres have obliterated central lumens., They are obliterated due to very walls which leaves no space inside them.

Occurrence: Xylem fibres are the components of xylem in all categories of vascular plants,

Functions: They are mechanical in function and provide support to the plant organs.

Xylem parenchyma : Cells of xylem parenchyma are living and thin-walled. Their Cell walls are made up of cellulose. They have a prominent nucleus and dense cytoplasm.

Occurrence: Xylem parenchyma is present in the xylem of all vascular plants.

Functions: The xylem parenchyma cells, as usual, store food materials in the form of reserve foods like starch or fat.

Phloem:

  • It is a living tissue that carries food materials, (in particular, sucrose, a sugar), from place it is available (source) to the places where it is needed (sink).
  • It transports the materials, usually from leaves to other parts of the plants like roots, growing tips of stem leaves, flowers, fruits etc.
  • The food prepared in the leaves through the process of photosynthesis needs to be transported to each and every part of plant body, which is facilitated by tissue called phloem.

Types of phloem : Like xylem, phloem is also classified into primary and secondary phloem on the basis of origin.

Primary phloem :

  • The phloem which is formed during primary growth of the plant body is called primary phloem.
  • It is further of two types on the basis of relative states of maturity
  1. Protophloem,
  2. Metaphloem.
  • The first formed primary phloem is called protophloem and later formed primary phloem is called metaphioem.

Secondary phloem

  • The phloem which is formed during secondary growth of the plant body is called secondary phloem.
  • It is formed by the vascular cambial ring (a lateral meristem)

Elements of phloem: Phloem is also a complex tissue-like xylem and is composed of the following four elements in angiosperms

  1. Sieve tube elements, B. Companion cells, C. Phloem fibres, D. Phloem parenchyma.

THE TISSUE SYSTEM

  • Till now we have discussed the various types of tissues in plants based on the types of cells.
  • present Now we will discuss how these different tissues associate with each other to work as a unit How these tissues form the tissue system.
  • what are the locations and functions of these different tissue systems in the body of flowering plants On the basis of structure and location, there are three types of tissue systems in plants
  1. Epidermal tissue system
  2. Ground or fundamental tissue system
  3. Vascular or fascicular or conducting tissue.
  • system These three tissue systems make the complete framework of the plants.
  • Each tissue system serves different functions.

Epidermal Tissue System

  • This tissue system forms the outermost covering of the plant body.
  • It is in direct contact with the external environment.

The epidermal tissue system comprises

(a) Epidermal cells,

(b) Epidermal structures, i.e., stomata

(c) Epidermal appendages – the trichomes and hair.

  • Epidermis : Epidermis is the outermost layer of the primary plant body.
  • It is usually single-layered, le.. composed of single layer of epidermal cells. However, it may be multilayered, i.e., composed of several layers of epidermal cells, e.g., Nerium, Ficus.
  • Stomata : Stomata are the minute structures present in the epidermis of leaves.
  • They are absent in the epidermis of roots Each stroma is composed of two bean-shaped or kidney-shaped cells known as guard cells, and a tiny stomatal pore.
  • The pore surrounded by two guard cells together form a stroma.
  • Guard cells: Guard cells are called so because they guard the opening and closing of the stomatal pore.
  • They are the living cells. They possess chloroplasts and regulate the stomatal movement.
  • These cells are generally bean-shaped or kidney-shaped but in grasses, the guard cells are dumb-ball.

FUNCTION OF STOMATA:

  • Stomata regulate the process of transpiration and gaseous exchange Transpiration is the loss of water by plants through the process of evaporation Gaseous involves the exchange of oxygen and carbon dioxide between plant and the environment.
  • The ones and entry and exit of gases occur through these epidermal structures called stomata Usually.
  • the lower surface of a dicotyledonous leaf has a greater number of stomata than the use surface while in a monocotyledon leaf.
  • they are about equal in number on both the surfaces.

ANATOMY OF DICOTYLEDONOUS AND MONOCOTYLEDONOUS PLANTS

  • For a better understanding of tissue organisation of roots and stems of dicots and monocots
  • to study the transverse sections of the mature zones of these organs

Anatomy of Root

  • Dicotyledonous root : TS. of a mature dicot root shows the following arrangement
  • Epidermis : It is the outermost layer of the body. It is usually single-layered.
  • The walls of many of epidermal cells protrude outwards in the form of tubular elongations.
  • Then unicellular tubular extensions are called root hairs which help in the absorption of water minerals from the soil.

Cortex: Below epidermis and upto endodermis several layers of parenchymous which comprise the cortex.

  • These are thread and are loosely packed which the free movement of water through them such an arrangement offers .

Endodermis: It is the innermost layer of the core which acts border the state.

  • All issues on the inner side of the endodermis such as precludes pith constitute the site Endoderm.
  • a single layer of barrel-shaped which

special thickenings of waxy material  in the radial and tangential washed strips Water molecules are unable to penetrate this layer in the area.

  • Pericycle : Next to endodermis the price which consists of these parenchyma cells it may be single-layered to several layered.
  • The cells of pericycle play an important role during the secondary grown of dicot roots cambium in the vascular bundies of dicot roots.
  • The developer at the time of secondary growth the form of ring like structure called cambial ring The parenchymatous cells of pericycle become meristematic.

Vascular bundles:

  • Xylem and phloem are arranged along different radii hence, radial vascular bundles are present Exarch condition of xylem is present in which metaxylem lies towards the centre and protoxylem towards the periphery.
  • There are two to six xylem and phloem patches but usually, their number varies from two to four. The root is called tetrarch when it has four xylem bundles, Triarch when it has three xylem bundles, diarchy when it has two xylem bundles in it.
  • In the given figure, the dicot root is tetrarch as it has four xylem bundles.
  • Conjunctive tissue: In between the xylem and phloem, patches of parenchymatous cells are present.
  • Pith: It is found in the centre. It is made up of parenchymatous cells which have intercellular spaces.
  • Pith is not well developed in the roots of dicotyledons. It is small and inconspicuous in them.

Monocotyledonous root :

The anatomy of the monocot root is similar to the dicot root in many respects. However, some differences are also found.

Epidermis: Outermost layer, bears large number of unicellular root hair cuticle and shoots are absent.

Cortex: Hypodermis is absent Cortex is made up of parenchymatous cell Endodermis is very distinct Made up of barrel-shaped cells having casparian strips.

Pericycle: It is also very distinct The cells of pericycle give me to lateral roots only as cambium is absent in the monocots

Vascular bundles: Vascular bundles are of radial type They are arranged along the different radius of the root Vascular cambium is lacking in them so the vascular bundles are closed Due to the absence of cambium, monocotyledonous roots do not undergo secondary growth.

Conjuctive tissue : In between the patches of xylem and phloem parenchymatous cell are present which comprise the conjuctive tissue

in Pith: Pith is large and well developed in roots of monocotyledonous plants .

Anatomy of Stem

  • Dicotyledons stem The transverse section of a typical young dicotyledonous stem shows the Epidermis.
  • The there most layer and is protective in function. It is made up of single layer
  • The ideal cells are circularized as they are covered with a thin cuticle appendages in the form of trichomes and a few stomata.
  • Young stems bear Cortex is several layered The cells arranged in multiple layers.
  • pericycle constitute the cortex it has three sub-zones.
  • Hypodermis the outer area of cortex which lies just below the epidermis.
  • It consists of collenchymatous cells in die stem.
  • The intercellular spaces are absent between these cells.
  • The bell walls are much thickened at the comers due to the hemicellulose and pectin.
  • The collenchymatous cells in hypodermis encasement to the young stems.
  • General cortex or cortical layers below hypodermis and above endodermis genera which consists of parenchymatous cell.
  • The cells are thin-wall possess intercellular space Endodermis layer of the cortex store starch grains.

Pericycle

  • it is present on the inner side (below) of the endodermis and above the phloem In between the endodermis and the phloem pericycle is present in the form of patches.
  • These patches are of semi-lunar (half moon) shape and comprise of sclerenchymatous cells.

VASCULAR BUNDLE:

  • A large number of vascular bundies are present in the dicot stem.
  • Each vascular bundles is made of xylem, phloem and a cambium between the two Xylem is situated towards the inner side of each vascular bundle and is endarch.
  • protoxylem lies towards the pith and metaxylem towards the periphery Hence, vascular bundies are conjoint, open and with endarch protoxylem The cambium consists of meristematic cells.
  • The division of meristematic adds to the phloem towards periphery and xylem towards the centre during the secondary growth.
  • A characteristic ring arrangement of vascular bundies is seen in the dicot stems The bundles are arranged in a ring manner around the central pith.

Medulla:

  • The central portion of the stem is occupied by a large number of parenchymatous cells which comprise the pion.
  • These cells are founded in shape and have large intercellular spaces Medullary rays or pith rays.
  • The cells of pith present in between the vascular bundies constitute the prays, also called medullary rays.
  • These parenchymatous cells are radially arranged in between the bundles and give the appearance of rays. The pith rays help in the radial conduction of food.
  • Monocotyledonous stem in the transverse section of a monocotyledonous stem following the present from outer to inner side.

Epidermis

  • It is the outermost layer which is made up of layer of cells.
  • The outer epidermal are covered with cuticle Stomata may be present.

Hypodermis

It lies below the epidermis it is constituted by the sclerenchymatous cells monocot stem (collenchymatous in dicots) Due to presence of sclerenchyma tissue provides the mechanical support to the stems.

Ground tissue

  • Main area of a monocot stem is occupied by the ground to Unlike dicot.
  • the ground tissue in monocot stems is not well differentiated into cortical layers, endoderm epicycloid and pith rays.
  • All cells lying inner to the hypodermis comprise the ground It is made up of parenchymatous cells.

Vascular bundles

  • A large number of vascular bundies are present. They are not arranged in the like manner as present in the dicot stems Rather the vascular bundies are found scattered in the whole ground tissue.
  • These are smaller in size and densely arranged towards the periphery but larger vascular bundles are loosely arranged towards the centre of the stem The bundles are almost oval in outline.
  • They have xylem and phloem elements but cambium is absent. Each vascular bundle is surrounded by a sheath made up of sclerenchymatous tissue.
  • It is called as bundle sheath The vascular bundle are conjoint and closed.
  • Hence, monocot stems cannot undergo the secondary growth Endarch xylem is present as protoxylem lies towards the centre and metaxylem lies towards the periphery Water-containing cavities in the vascular bundle is a characteristic feature of monocot stems.
  • Phloem consists of sieve tubes, companion cells and phloem fibres Phloem parenchyma is Absent.
  • Ground tissue Differentiated into cortex and pith Not differentiated into cortex and Collenchymatous pith.
  1. Hypodermis
  2. Single layered Sclerenchymatous
  3. Endodermis Absent Made up parenchymatous.
  4. Pericycle sclerenchymatous cells Absent.

Anatomy of Leaf

  • The leaf is usually a flat structure. It is the main photosynthetic organ in the plants.
  • Leaf has epidermis on both of its surfaces. The photosynthetic tissue of a leaf is sandwiched between its upper and lower
  • epidermis and is well supplied by the vascular system.
  • The photosynthetic tissue in leaf possesses chloroplasts It is noteworthy that in a leaf, xylem always faces upper epidermis while phloem is towards lower epidermis also.
  • The internal structure of a leaf is studied in its vertical section on the basis of anatomy, leaves are of two types.

Dorsoventrally

  • Dorsoventrally leaves are found in the dicotyledonous plants.
  • Such leaves generally remain horizontal and sunlight falls on their upper surface.
  • Upper surface of a leaf is called ventral surface or adaxial.

SECONDARY GROWTH

  • The growth of roots and stems in length with the help of apical meristems is called the primary growth whereas the growth of roots and stems in girth with the help of lateral meristems is called the secondary growth.
  • dorsoventrally leaves as their dorsal and ventral surfaces differ in colour and anatomical features and are therefore, distinguishable into two different surfaces.
  • Upper surface is darker green as compared to the lower surface.

Isobilateral :

  • Isobilateral leaves are found in the monocotyledonous plants.
  • Such leaves generally remain vertical. These are called the isobilateral leaves as their both surfaces (upper and lower) are equally green and similar to one another.
  • All plants undergo primary growth but apart from primary growth.
  • The most of the dicotyledonous plants exhibit secondary growth also Generally secondary growth does not occur in monocots due to the lack of vascular cambium in the Intrafascicular cambium.
  • The interfascicular cambium and cork cambium are the lateral meristems that participate in the secondary growth of dicots.
  • After the formation of primary tissues, these lateral meristems become active and start dividing to form the secondary tissues.
  • The secondary tissues include secondary xylem, secondary phloem, secondary medullary rays, cork and secondary cortex.
  • These all tissues constitute the secondary body of most dicotyledons Secondary growth occurs in the stems and roots of gymnosperms also.

REFERENCES

  1. https://ncert.nic.in/textbook/pdf/kebo106.pdf