Anatomy of Flowering Plants PDF

1 Anatomy of Flowering Plants Introduction: Higher Plants have complex body organization Definition that is made up of many cells that form tissues, tissues give rise to organs and organs to organ Anatomy: The branch of Biology systems. This whole...

1 Anatomy of Flowering Plants Introduction: Higher Plants have complex body organization Definition that is made up of many cells that form tissues, tissues give rise to organs and organs to organ Anatomy: The branch of Biology systems. This whole process takes place by cell that deals with the study of division and cell differentiation. In the beginning, internal organization of plants. all the newly formed cells arise from meristematic cells that are almost alike. During maturation, they undergo various structural changes by a process called differentiation. Differentiation leads to the formation of different kinds of cells and tissues from the parent cell where each cell performs a specific function. So, differentiation leads to physiological differentiation or division of labour i.e., performing special functions. Gray Matter Alert!!! y The branch of Biology that deals with the study N. Grew (1682): Father of Plant of internal structures of organisms is called Anatomy; coined the terms Anatomy. ‘Tissue’ and ‘Parenchyma’. y Nehemiah Grew, is known as the “Father of Plant Nageli (1858): Gave the terms anatomy” and also coined the term ‘Tissue’. Meristems, Xylem and Phloem. Plant Tissues y A group of similar or dissimilar cells having a common origin and in cooperation with one another, perform a similar function is called tissue. y Depending upon the capacity to divide, plant tissues have been classified into two fundamental types: Definition Anatomy of Flowering Plants PLANT TISSUES Tissue: A group of similar Meristems or Permanent or dissimilar cells having Meristematic tissues Tissues a common origin and in cooperation with one another, ever dividing non-dividing perform a similar function is tissue tissue formed after called tissue. differentiation 1.  Meristematic Tissues (Meristems) y A meristematic tissue is composed of similar Gray Matter Alert!!! cells that are capable of dividing and forming new cells throughout life of a plant. Differentiation: When the y A plant starts its life as a unicellular structure cells undergo anatomical and i.e., fertilized egg cell that develops into embryo, morphological changes and lose which develops into a young plant. the capacity of division. Meristems (Gk. Meristos-divisible) or meristematic tissues can be defined as the tissues made up of a group of live, thin-walled and similar cells that divide continuously forming new cells. Characteristics of Meristematic Tissue: y The cells can divide throughout their life. y These cells are thin-walled and are compactly arranged i.e., without intercellular spaces. Previous Year’s Questions y These cells have only primary cell wall which is made up of cellulose. Promeristem gives rise to which y These cells may be isodiametric, rounded, oval or type of meristem? polygonal in shape. (1) Lateral y Cytoplasm is dense means vacuoles are either (2) Primary absent or are exceedingly small. (3) Apical y The cells do not store reserve food as they are in (4) Secondary highly active stage. y Ergastic substances are usually absent in meristematic cells. Classification of Meristems Based on their origin, position, and functions: 1. MERISTEMS ON THE BASIS OF ORIGIN ARE OF TWO TYPES: Promeristem (Primordial Meristem or Embryonic Anatomy of Flowering Plants Meristem) Rack your Brain y These are groups of meristematic cells in germinating embryos or young seedlings. y Promeristems give rise to primary meristems viz. Why meristematic cells are apical and intercalary meristems. unable to store food? 2.  CLASSIFICATION OF MERISTEMS Based on Origin Based on Position Based on Function Promeristem Apical Meristem Protoderm Intercalary Meristem Procambium Primary Meristem Lateral Meristem Ground Meristem Secondary Meristem y They are represented by apical meristems (root Definition apical meristem and shoot apical meristem) and intercalary meristems and intravascular cambium Primary Meristem: It appears (in the open vascular bundles). early in the life of a plant and y The primary meristems give rise to different retains the capacity of division primary permanent tissues (except interfascicular throughout the life, derived from cambium). the Promeristem. y The activity of primary meristem (i.e., apical meristem and intercalary meristem) is responsible for length-wise growth called primary growth. y The activity of fascicular cambium results in an increase in girth (secondary growth). Previous Year’s Question Secondary Meristem Secondary xylem and phloem in y Derived from permanent tissues (like parenchyma) dicot stem are produced by by the process of differentiation. (1) Phellogen y Examples: (2) Vascular cambium ⚪ Interfascicular cambium (in dicot stem) (3) Apical meristem ⚪ Vascular cambium (in dicot roots) (4) Axillary meristem ⚪ Cork cambium or phellogen ⚪ Wound cambium ⚪ Accessory cambium. Definition Anatomy of Flowering Plants These all are lateral in position and give rise to secondary permanent tissues that result in the Secondary Meristem: Derived growth in thickness (secondary growth). from permanent tissues (like ⚪ Interfascicular cambium develops from parenchyma) by the process of primary medullary cells (parenchymatous differentiation. It appears later cells) found in primary dicot stems. It forms in the life of a plant. fascicular cambium ring by joining with 3.  interfascicular cambium. The fascicular cambium ring gives rise to secondary vascular Definition tissues (secondary xylem, secondary phloem). ⚪ Vascular cambium in dicot roots, arises from Cork Cambium: Meristematic conjunctive parenchyma and it acts like tissue (secondary meristem) fascicular cambium ring of dicot stems. formed by the process of ⚪ Cork cambium originates from the outer de-differentiation from the layers of the cortex, epidermis or sometimes parenchymatous cells (simple pericycle and gives rise to periderm. permanent tissue) of cortex. ⚪ Wound cambium arises from the cells surrounding any injury or wound, helpful in mending the injured tissue. ⚪ Accessary cambium develops from the ground tissue of monocot stems that show abnormal secondary growth, e.g., Yucca etc. 2. MERISTEMS ON THE BASIS OF POSITION Meristems are classified into three types on the basis of position : Apical Meristems: y These arise from Promeristem and form growing points at stem apex and roots apex. y Being terminal in position, these meristems are called apical meristem. y Present at root tips but root apical meristems are sub-terminal in position (located below the Gray Matter Alert!!! root caps) y Apical meristems are responsible for length-wise The initiation of growth takes growth of plants. place by the meristematic activity of a single apical cell (as Intercalary Meristems in higher algal forms, bryophytes y These are the cells of the apical meristems, and pteridophytes) or by a group separated during the formation of permanent of apical cells or apical initials Anatomy of Flowering Plants tissues. (in spermatophytes). y Present at the base of leaves (e.g., Pinus), above the nodes (e.g., Grasses) or just below the nodes (e.g., Mint). y Intercalary meristems assist in lengthening of plant parts. y Helpful in keeping the stems of cereals, erect. y These meristems are short lived and are used up 4.  in the formation of plant parts. y Exception: The intercalary meristems present at Definition the base of Pinus leaf remain active throughout the life of the leaf. Lateral Meristems: These are located along the lateral sides Lateral Meristems of stems, branches and roots. y located along the lateral sides of stems, branches These meristems increase the and roots. girth or diameter of the plant y These meristems increase the girth or diameter organs. of the plant organs. y Lateral meristems are cylindrical, running throughout the plant body. y Both primary and secondary in origin. ⚪ Intrafascicular cambium or vascular cambium is primary meristem formed by differentiation process. Also called as Primary lateral Meristem. Previous Year’s Question ⚪ Marginal Meristem: At the leaf margins and helps in expansion of leaf lamina. ⚪ Interfascicular cambium in stems, vascular Totipotency is present in ______. cambium in roots, accessory cambium, cork (1) Meristem cambium and wound cambium are Secondary (2) Cambium Meristems. (3) Phloem ⚪ Secondary meristems are formed by (4) Cork dedifferentiation process. 3. Meristem types (Based on Function): Haberlandt (1914) classified primary meristem into three types: Protoderm y It is the outermost layer of promeristem or apical meristem. Gray Matter Alert!!! Anatomy of Flowering Plants y It leads to epidermal tissue system. y Epidermal tissue system includes epidermis, root hair, stem hair etc. Gottlieb Huberlandt, is considered as the “father of tissue culture”. Procambium y It occurs in the form of isolated longitudinal strands of elongated cells, near the central region. 5.  y It develops into primary vascular tissues i.e., primary xylem and primary phloem. Rack your Brain  round or Fundamental Meristem G Which of the following is in low y It lies inner to the protoderm and surrounds the concentration in the cells of procambium. quiescent center? y It leads to the ground tissue system viz. DNA, proteins, or RNA. endodermis, hypodermis, cortex, pericycle, medullary rays and pith. ROOT CAP y The root cap cells are made up of parenchyma and have shorter life span. Previous Year’s Question y Root cap cells possess starch grains that are believed to be responsible for the geotropic Stem of grass and related plants response of the root. elongate by the activity of y The root cap acts as protective shield between __________. the soil and the apical meristems. (1) lateral meristem y It appears as thimble and protects the root (2) Apical meristem meristem. It protects the root meristems. (3) Both apical and intercalary y The cells of the root cap secrete a mucilaginous meristem substance that acts as a lubricant and helps the (4) Intercalary meristem tender root tip to penetrate deep into the soil. Quiescent Centre y In many cases, a tiny region with extremely low mitotic activity is present in the center of the root apex. y This region is called quiescent center (Clowes, 1961). y In the cells of quiescent center, there is quite little synthesis of proteins, RNAs and DNAs. y Quiescent center may act as a reserve meristem. Anatomy of Flowering Plants y Due to the presence of quiescent center, root apical meristem is cup shaped or hemi-spherical in shape. Root Apex (Root Apical Meristem) y Root apex is found at the tip of main root and at the tip of branches in tap root system. Figure: Structure of Root Apex 6. y Root apical meristem is subterminal in position. y Secondary root branches develop much Rack your Brain behind the apex, from the deeper layers of the root (pericycle and endodermis), hence are Histogen found at the tip of root endogenous in origin. apical meristem is ___________. (plerome/periblem/calyptrogen/ Meristematic regions in the root apical meristem: Dermatogen). y Protoderm: It gives rise to epidermal tissue system like epiblema, root cap and root hairs. y In monocots, the root cap is derived from a special meristematic region at the end of the root called calyptrogens (calyptras-cap, gen-producing). y Procambium: Gives rise to primary vascular tissues: primary xylem and primary phloem. y Ground Meristem: It helps in the formation of ground tissue system viz. hypodermis, Gray Matter Alert!!! endodermis, pericycle, pith etc. Calyptrogen, a special Classification of Meristems meristematic region at the end of (Based on Plane of Division) the roots in monocot plants that y Rib-meristem or File meristem: forms root cap. Meristem in which anticlinal division occurs only in one plane. MERISTEMS Based on Plane of Division Rib-meristem Plate meristem Mass-meristem or or File meristem Block meristem E.g., leaf blades in Angiospermic plants E.g., tunica E.g., young embryos, Previous Year’s Question endosperm The cells of this meristem divide perpendicular Intercalary meristem causes ___. Anatomy of Flowering Plants to the longitudinal axis of the plant organ. As a (1) Secondary growth result, parallel layers of cells (just like ribs) are (2) Primary growth produced. (3) Apical growth Rib meristem produces petiole of leaves (organs (4) Secondary thickening of cylindrical form) etc., cells of cortex and pith. 7.  Tunica is also a type of rib-meristem. y Plate meristem: Meristem which divides anticlinally into two planes, forms flat structure. This leads to an increase in cell number per layer. This division causes the meristem to grow as a sheet but not in thickness producing flat organs Gray Matter Alert!!! like leaf. y Mass-meristem or Block meristem: Meristem which divides in all possible planes resulting in Ground meristem exhibits two an increase in the volume of plant body (organ). growth forms: plate and rib The derivative cells are isodiametric or spherical meristem. or may not have definite shape. For Example: young embryos, endosperm, reproductive organs etc. Classification of Meristems (On the Basis of Rate of Division) Cyto-Histological Zonation Theory: Proposed by Foster 1. Summit: This region is located at the apex. Rate of division: slow 2. Flank: This region is located behind the summit region. Rate of division: fast Plays a crucial role in formation of leaf primordia. Role of Summit and Flank in the formation of Vegetative Shoot Apex (Shoot Apical Meristem) y Present at the tip of stem and branches, as a terminal bud. Figure: Longitudinal section of vegetative shoot apex showing distribution of y Conical or dome-shaped, always covered by meristems based on the functions. Anatomy of Flowering Plants young leaves, arising from its sides. These leaves protect the apex. y Cell division is rapid in flank region, giving rise to leaf primordial. y Each leaf primordium has axillary meristem or axillary bud in its axil. Axillary buds remain dormant for some time till the plant attains a particular size. 8. y The apical meristems add new tissues and elongate the shoot. Gray Matter Alert!!! Role of Summit and Flank in the formation of The period between the Reproductive Shoot Apex (Floral Bud) appearance of two successive leaf During reproductive phase, the vegetative shoot primordia is called plastochron. apex changes into reproductive shoot apex or a single floral bud. The cells of summit region (topmost region), that were inactive during the vegetative phase, start dividing actively and give rise to primordium of stamens and carpals. In flank region, leaf primordia are replaced Gray Matter Alert!!! by primordial of sepals and petals. Thus, the entire apical meristems undergo morphological Differentiation: When the changes. cells undergo anatomical and morphological changes and lose the capacity of division. Anatomy of Flowering Plants 9.  THEORIES TO EXPLAIN STRUCTURAL ORGANIZATION AND DEVELOPMENT OF SHOOT APICAL MERISTEM Based on the rate of division Apical Cell Theory Histogen Theory Tunica Corpus Theory Proposed by Hanstein(1870) Proposed by Schmidt Proposed by and (1924) Hofmeister, and the apical meristems consists According to histogen theory of three distinct histological zones called HISTOGENS supported by Nageli and Wolff Dermatogens two zones are in the apical meristems single apical cell leads to the development of Periblem Tunica Corpus entire plant body. Plerome Apical Cell Theory: Proposed by Hofmeister and supported by Karl Nageli and Wolff. Gray Matter Alert!!! y According to Nageli (1858), the activity of single apical cell leads to the development of entire Histogen theory is true only for plant body. root apex. y This theory is applicable to higher algal forms It is not applicable for shoot (e.g., Fucus, Dictyota & Sargassum) and most of apex of higher plants; as in the Cryptogams, but not to the phanerogams most of the Angiosperms and (e.g., Angiosperms and Gymnosperms). Gymnosperms, the shoot apex y Histogen Theory: Proposed by Hanstein (1870) is not differentiated into three According to histogen theory, the apical histogens. meristems consist of three distinct histological zones called histogens. (a) Dermatogen: The outermost mantle like layer Gray Matter Alert!!! of cells, usually single cell in thickness. It gives rise to epidermis or epiblema in roots, Calyptrogen: Fourth type of Anatomy of Flowering Plants cortex and endodermis. histogen, found in root apex of (b) Periblem: It lies under the dermatogen. grasses (monocots). Calyptrogen Forms cortex which includes hypodermis, forms root cap in roots of general cortex and endodermis. monocot plants. (c) Plerome: The central zone (innermost region) Root cap is developed from of cells is called plerome. It forms vascular Dermatogen in dicot roots. cylinder (pericycle, vascular tissues and medullary rays) including pith. 10.  Haberlandt (1914) proposed the following terms: (i) Protoderm for dermatogen (ii) Ground meristem for periblem (iii) Procambium for plerome Examples w.r.t exception in number of dermatogens- In Ranunculus, only one histogen is found and in Casuarina two histogens are found. y Tunica Corpus Theory: Proposed by Schmidt Previous Year’s Question (1924). y According to this theory, only two zones are in Root cap is formed by __________. the apical meristems: TUNICA and CORPUS. (1) Dermatogen (1) TUNICA: (2) Calyptrogen y The cells of tunica are small. (3) Wound cambium y They divide anticlinally in one plane (at right (4) Vascular cambium angles to the longitudinal axis) only and thus, help in surface enlargement. Unicellular Tunica: Cells are arranged in one layer. The cells derived from tunica, give rise to epidermis of both stems as well as leaves. Multilayered Tunica: More than one layer in thickness. y The outer layer differentiates into epidermis. y The inner layers contribute to the leaf primordium Rack your Brain and cortex. (2) CORPUS How are the cells of meristem y The cells of corpus are larger than the cells of different from the rest of the Tunica. cells of a plant? y They divide in different planes due to which the volume increases. The cells derived from corpus give rise to Anatomy of Flowering Plants PROCAMBIUM and GROUND MERISTEMS. (a) PROCAMBIUM y Composed of somewhat narrow, elongated cells containing dense cytoplasm. y The cells are arranged parallel to the longitudinal axis of the stem. 11.  y Procambium gives rise to primary phloem, primary which develops pith. xylem and intra-fascicular cambium between ⚪ Peripheral Meristem: Middle xylem and phloem (Gymnosperms and dicots). region that forms cortex, (b) GROUND MERISTEM pericycle and vascular tissues. y Composed of thin walled parenchymatous cells. PERMANENT TISSUES (Mature Tissues) y Differentiates into pith in the center, pericycle, y A permanent tissue may be made endodermis, cortex and hypodermis respectively up of similar or dissimilar cells. towards the outer side. y Have lost the capacity of division. y Have attained a permanent MANTLE CORE THEORY shape and size by the process of differentiation. Put forward by Popham and Chan for Shoot Apex y Cells may be living or dead. y Here, ‘MANTLE’ is compared to Tunica. y The cells are thin or thick-walled. y Corpus is compared with CORE. y The cytoplasm is vacuolated and y Core is divided into three regions: dilute. ⚪ Sub Apical Meristem: Present below the y Intercellular spaces may or may Mantle and regenerates damaged Mantle. not be present. ⚪ Central Zone Meristem: Inner-most region Kinds of Permanent Tissue: Anatomy of Flowering Plants 12.  I. SIMPLE PERMANENT TISSUES: A simple permanent tissue is homogeneous in nature viz. made up of similar types of perma- Previous Year’s Question nent cells. These carry out the same or similar set of Pistia floats on the surface of functions. water due to the presence of __________ tissue in its petiole. Types of Simple Permanent Tissues: (1) Parenchyma y Parenchyma (2) Prosenchyma y Collenchyma (3) Aerenchyma y Sclerenchyma (4) Chlorenchyma (a) Parenchyma y It is made up of thin-walled, isodiametric (equal diameter) living cells. The cells may be oval, rounded or polygonal in shape. y Cell wall is cellulosic, thin and elastic. y Small intercellular spaces are generally present between the cells for exchange of gases. Definition Plasmodesmata are commonly present. y Each mature parenchyma cell has peripheral Permanent Tissue: A group of cytoplasm due to the presence of a large vacuole similar or dissimilar cells which and nucleus shift towards the periphery. has lost the capacity of division. y Parenchyma occurs in non-woody or soft areas of the plant organs. y It is also called fundamental tissue as it forms the ground tissue in which the other plant tissues are embedded. Functions of Parenchyma y Storage of food y Provides turgidity. Anatomy of Flowering Plants Modified Parenchyma y Chlorenchyma y Prosenchyma y Aerenchyma y Xylem parenchyma and phloem parenchyma y Storage parenchyma 13.  Functions of Modified Parenchyma: (i) Chlorenchyma Parenchyma cell may contain chloroplasts and Definition takes part in photosynthesis. Such parenchyma cell is called chlorenchyma. Chlorenchyma: y The chlorenchyma of leaves is termed as Parenchyma cells that contain mesophyll. chloroplasts and take part in y Chlorenchyma of leaves of dicot plants is of two photosynthesis. types: (a) Palisade Parenchyma: Compactly arranged columnar cells. Intercellular spaces absent Abundant Chloroplasts (b) Spongy Parenchyma: Loosely arranged spherical cells. large intercellular spaces are present. Number of chloroplasts is less than the Previous Year’s Question palisade parenchyma. (ii) Prosenchyma y Parenchyma modified into fiber like extended, Palisade parenchyma is an slightly thick-walled cells. example of ________. y It provides turgidity and strength. (1) Parenchyma (iii) Aerenchyma (2) Chlorenchyma y This parenchyma consists of loosely arranged (3) Aerenchyma cells with large air cavities. (4) Prosenchyma y Aerenchyma stores air and provide buoyancy to the aquatic plants. y Found in aquatic and some land plants (e.g., petiole of Canna, banana). y (iv) Xylem Parenchyma and Phloem Parenchyma y Associated with either xylem or phloem. y They help in storage of food and lateral conduction of water and food. Anatomy of Flowering Plants (v) Storage Parenchyma y It is specialized parenchyma that stores tannins, Gray Matter Alert!!! oils and calcium oxalate crystals. y Cells of this parenchyma are called idioblasts. Schleiden (1839) coined the term y Idioblasts are enlarged isolated parenchyma cells ‘Collenchyma’. that are different from the surrounding cells. 14.  (b) Collenchyma y It is made up of living cells which possess unevenly thickened cell walls. y The thickening is made up of cellulose, pectin and hemicellulose. y The cells are either isodiametric or somewhat elongated. y They appear circular, oval or angular in transverse section. Each cell has a large central vacuole and peripheral cytoplasm. y Collenchyma occurs below the epidermis in the petiole, leaves and stems of herbaceous dicots. Gray Matter Alert!!! It is prominent below the ridges. Mettenius (1805): Discovered and Functions of Collenchyma: gave the term ‘Sclerenchyma’. It gives mechanical strength and elasticity to the organs. y Sometimes, collenchyma cells possess chloroplasts and are photosynthetic in function e.g., leaf petiole, epicarp of raw fruits. Thick cell wall (c) Sclerenchyma (Gk. Scleros-hard, enchyma- Lumen tissue) y It is a simple permanent tissue of dead and highly thick-walled cells. y The thickening of walls may be made up of cellulose or lignin or both. y Several unlignified or unthickened area called pits are often present on the walls. Fibre y At maturity, these cells lose protoplasmic contents and become dead. y Often the thickening in the cells is more so, central cavity (lumen) is obliterated. Anatomy of Flowering Plants Lumen Rack your Brain Thick Which type of permanent tissue is found Cell wall A sclereid in Sapota? 15.  Function of Sclerenchyma Sclerenchyma is the chief mechanical tissue in plants and can tolerate all types of physical Previous Year’s Question stress. Types of Cells in Sclerenchyma Sclereids belong to __________. It has two types of cells: sclerenchyma fibres (1) Collenchyma and sclereids. (2) Xylem (i) Sclerenchyma Fibres: (3) Sclerenchyma ⚪ Elongated, narrow, spindle shaped, thick- (4) Sclerenchyma fibres walled cells. ⚪ Pointed or tapering ends. ⚪ Occur in longitudinal bundles (They may also occur singly among other cells). Gray Matter Alert!!! ⚪ Generally, 1-2 mm in length. In special cases such as in hemp, they may attain a length of 90 cm. Fibres are present in the form of ⚪ These are probably the longest cell in patches in the pericycle of dicot plants. stems, cortex and bundle sheath (ii) Sclereids or Sclerotic cells of monocot stems and in xylem ⚪ They are short, highly thick-walled, and phloem of stems. spherical or irregularly shaped sclerenchymatous cells. Long fibres are of great ⚪ Their wall has branched or un-branched commercial importance as they simple pits. are the source of natural fibres ⚪ Sclereids may occur singly or in groups. like jute, hemp, coir etc. ⚪ They are commonly present in hard coverings of seeds and nuts, endocarp of stony fruits and pulp of many fruits such as Guava, Pear and Sapota etc. ⚪ The grittiness of the pulp in these fruits Rack your Brain is due to the presence of sclerotic cells. Sclereids also occur in cortex, phloem, Which type of permanent tissue Anatomy of Flowering Plants and pith of certain plants. is found in pods of legumes? ⚪ They provide stiffness to the parts in which they occur. 16.  TYPES OF SCLEREIDS DEPENDING ON SHAPE AND SIZE Unbranched, isodiametric with branched Brachysclereids or (ramiform) pits, e.g., grit of Apple, Pear, and Stone cells guava. Elongated and columnar or rod like, e.g., Macrosclereids epidermal covering of legume seeds. Bone-like columnar with dilated ends. e.g., sub- Osteosclereids epidermal cells of some legume seeds. Irregularly branched or star like e.g., leaves and Astrosclereids petioles of some aquatic plants. Filiform sclereids Fibre-like and scantily branched e.g., Olea. II. COMPLEX PERMANENT TISSUES y A complex permanent tissue is composed of Definition more than one type of cells which have lost the capacity of division. Complex permanent tissue is y It works as a unit that aids in transportation of composed of more than one water, minerals and food. type of cells which have lost the y It provides mechanical support. capacity of division. Types of Complex Permanent Tissue Xylem y It is also called wood and forms the bulk of the roots and stems of vascular plants. y It is a conducting tissue and forms a continuous channel through the roots, stems, leaves, flowers Previous Year’s Question Anatomy of Flowering Plants and fruits. y Conduction in xylem is unidirectional (from roots Living part of xylem is __________. to the shoot) (1) Xylem tracheids y Xylem consists of different types of cells which (2) Xylem vessels may be both living (i.e., xylem parenchyma) and (3) Parenchyma non-living (i.e., tracheids, vessels and xylem (4) None of these fibres) 17.  Components of Xylem COMPONENTS OF XYLEM Tracheary Elements Xylem Parenchyma Xylem Fibres or or Wood Parenchyma Xylem Sclerenchyma Tracheids Vessels (i) Tracheary Elements (Xylem): Conducting elements of xylem are recognized as two types: Tracheids and Vessels. (a) Tracheids (Dead Element) y The tracheids are elongated, spindle shaped dead cells with narrow blunt ends. y They possess hard lignified walls and wide lumen. y The walls of tracheids have various types of thickening for mechanical strength. Unthickened areas on their walls allow rapid movement of sap from one cell to another. y In angiosperms, only few tracheids are present. y Gymnosperms have only tracheids. y Tracheids conduct water and minerals in the plants. y These also provide mechanical strength. Types of Tracheids (Depending Upon Thickenings): Gray Matter Alert!!! Anatomy of Flowering Plants (a) Annular – The thickening material (lignin) is deposited in the form of rings. Harting (1839): Discovered sieve (b) Spiral-The thickening is laid down in the form tube. of spiral or helix. Sanio (1863): Discovered and (c) Reticulate –The thickening is present in the gave the term Tracheid. form of a network. 18.  (d) Scalariform-The thickening is laid down in the form of transverse bands to give a ladder Previous Year’s Question like appearance. (e) Pitted –The thickening is uniform except Vessels and fibres occur in small, unthickened areas called pits. __________. (1) Xylem of angiosperms Pits in Xylem (2) Xylem of gymnosperms y The pits are formed in pairs laying one against (3) Xylem of pteridophytes the other, and appear circular, oval or angular in (4) All the above surface view. y The area of the primary wall and middle lamella present in between a pair of pits is called pit membrane or closing membrane. y The pits have several sub-microscopic pores for the translocation of substances. TYPES OF PITS Simple Pits Bordered Pits Uniform width of The pit cavity is broader towards the the cavity or pit base with a narrow opening. The pit chamber membrane of bordered pit develops a swelling in the middle called TORUS. It helps in the regulation of the movement of substances. (b) Vessels or Tracheae (Dead element) y These are much elongated, tubular channels with wide lumen. y The vessel elements are joined end to Gray Matter Alert!!! Anatomy of Flowering Plants end and have perforated end walls. y The perforated end walls are called Xylem vessels are absent in perforation plates. Gymnosperms. y The wall of vessels is lignified. y Vessels help in quick movement of water and minerals. y Vessels also provide mechanical strength. 19.  y The vessels are rounded in monocots and polygonal in dicots, in cross-section. y Vessels are present in angiosperms only. Types of Perforation Plates in Vessels y Simple Perforation Plate: When the vessel has a single large opening at its ends. y Multiple Perforation Plate: In few angiosperms, the end wall of vessel bears several perforations Previous Year’s Question e.g., Magnolia. Which pair has lignin __________. Types of Thickening in Vessels (1) Tracheids & collenchyma y Annular (2) Sclerenchyma & sieve tube y Spiral (3) Sclerenchyma & tracheids y Reticulate (4) Parenchyma & endodermis y Scalariform y Pitted (Most common type of thickening in vessels) 1. Xylem or Wood parenchyma (Live Component) y Parenchymatous cells associated with xylem. y They may be thin-walled or thick-walled with simple pits. y Assists in the lateral conduction of water or sap. y Xylem parenchyma stores food. Rack your Brain 2. Xylem or Wood fibres (Dead Component) y These are sclerenchymatous fibres. What is a common feature y Elongated, thick-walled and have narrow lumen. between vessel and sieve tube y Provide mechanical support. elements? Types of Primary Xylem Based upon origin, and internal structure: Anatomy of Flowering Plants 1. Protoxylem (Gk, protos-first, xylem-wood): First formed xylem. It is made up of small tracheids and vessels, thickening is usually annular or spiral. Thickenings start much before the complete formation of xylem vessel. 2. Metaxylem (Gk, meta-after, xylem-wood): The later formed xylem. 20.  It consists of larger tracheids and vessels, thickening may be reticulate, scalariform and Previous Year’s Question pitted. The thickening of cell walls occurs after Protoxylem is towards pith and complete elongation of the xylem cell. metaxylem towards periphery, the xylem is __________. Types of Xylem: (Based upon the position of (1) Exarch protoxylem in relation to metaxylem) (2) Endarch 1. Exarch- Protoxylem lies towards the outer (3) Mesarch side of metaxylem e.g., as in roots. (4) Centrach 2. Endarch-Protoxylem occurs towards the inner side of metaxylem e.g., as in stems. 3. Mesarch-Protoxylem is present in the middle of metaxylem e.g., ferns. Phloem y Also known as bast or laptone. y Phloem is a ‘live’ complex permanent tissue. y It helps in the translocation of food materials within the plant. y Translocation of food is bidirectional, from source to the sink and vice-versa COMPONENTS OF PHLOEM Sieve Tubes Companion Phloem Phloem Cells Parenchyma Fibres 1. Sieve Elements: They are the main food conducting elements and are recognized into two types-Sieve tubes and Sieve cells. Anatomy of Flowering Plants Sieve tubes (live component) y They are elongated tubular channels. y Each sieve-tube is made up of several cells called sieve-tube members, joined end to end. y Their end walls are generally bulged out and may be oblique or transverse. y The end walls have many large pores or sieve pits and are known as sieve plates. 21.  y At maturity, the sieve pores become impregnated with callose. y The protoplasts of the adjacent members relate to each other through the pores of sieve plates. y Each sieve tube is always associated with companion cells. y A mature sieve element (sieve cells or sieve tube) has a peripheral cytoplasm without nucleus. Previous Year’s Question Though nucleus is present in young developing sieve cells. Companion cells are usually seen y The central part of the sieve element is occupied associated with __________. by a network of canals containing fibrils of a (1) Fibres special protein called p-proteins (p-phloem). (2) Tracheids y During wounding along with callose, p-proteins (3) Vessels help in sealing. (4) Sieve tubes y Sieve elements take part in the transport of organic food. Sieve Cells y Found in non-flowering plants viz. Pteridophytes and Gymnosperms. y These are elongated cells having several perforated areas called Sieve Areas, throughout the lateral walls and end walls. y Unlike Sieve tubes, Sieve cells are not present in linear rows. Gray Matter Alert!!! y The companion cells are not present with the sieve cells. Sieve Cells are found in 2. Companion Cells (Live component) Gymnosperms and Pteridophytes. y Elongated thin-walled parenchymatous cells that In these plants, Sieve tubes are lie on the sides of the sieve tubes. absent. y Through plasmodesmata (present on their Anatomy of Flowering Plants common longitudinal walls), these are closely associated with the sieve tubes. These have dense cytoplasm and prominent nuclei. y The nuclei of companion cells control the metabolic activities of sieve tubes through plasmodesmata. y The companion cells also play an important role in the maintenance of pressure gradient in the sieve tubes. 22. y Companion cells are present in angiosperms only. They are replaced by modified parenchyma cells (called albuminous cells) in non-flowering plants. 3. Phloem Parenchyma y These are ordinary parenchyma cells, which are Rack your Brain intermingled with sieve element. y These store food and assist in the conduction of From which of the following , the food, in lateral direction. phloem parenchyma is absent? y Phloem parenchyma is absent in most of the Dicot root, dicot stem, dicot leaf, monocots and some herbaceous dicots. monocot leaf. 4. Phloem Fibres (Bast Fibres) y Sclerenchymatous fibres. y Provide mechanical strength. y These occur in groups as sheets or cylinders. y The textile fibres of flax, hemp and jute are phloem fibres. y They are obtained after retting the plants in water and are used for making ropes, twines, threads, and course textiles. Protophloem: This is the outer portion of the phloem, consisting of narrow tube elements. Metaphloem: This is the inner portion of the phloem, made up of broader sieve tube elements. TISSUE SYSTEM Previous Year’s Question 1. Epidermis y Epidermis is usually single layered. Fibres associated with phloem are y It is Multilayered in the leaves of some tropical (1) Hard fibres plants (e.g., Ficus, Nerium etc.) and in the velamen (2) Wood fibres of the roots of epiphytic plants. (3) surface fibres y Cuticle is present on the outer side of the (4) Bast fibres Anatomy of Flowering Plants epidermis of aerial parts of the plants made up of cutin. Function of Epidermis (along with cuticle): y Protects the inner cells against loss of water. y Protects against mechanical injury. y Protects from the attack of pathogens. y Protects from leaching effect of rain. 23.  TISSUE SYSTEM In monocot and dicot roots, on the basis of principle of division of labour, Sachs (1975) classified tissues into three basic tissue Epidermal tissue system Ground or fundamental Vascular tissue system tissue system Ground tissue is Epidermis differentiated into Roots Pericycle Vascular cylinder and Dicot Stems usually single layered e.g., Hibiscus leaf Hypodermis Vascular Bundles Multilayered e.g., leaves Cortex of Ficus, Nerium Endodermis Pith Medullary Ray Radial V. B. Conjoint V.B. Epidermal Outgrowths Collateral Components Bi-Collateral Trichomes Emergence, of Phloem Or Hairs Prickles Open Vascular Closed Vascular Amphivasal V.B. Amphicribal V.B. Bundle Bundle 2. Epidermal Outgrowths They are of two types. (a) Trichomes or Hairs: The epidermal hairs of aerial part of plants can be- Previous Year’s Question y Unicellular or Multicellular y Branched or un-branched Trichome takes part in __________. (1) Transpiration and exchange of Functions of Trichomes gases Anatomy of Flowering Plants y Protect the plant organs against water loss. (2) Protection and reduction of y Protect against sudden fluctuation in atmospheric transpiration temperature. (3) Exudation of water drops (4) Desiccation (b) Emergences or Prickles y Multicellular y Sharp and stiff epidermal outgrowths, which contain some inner tissues. 24. y They protect the plant against grazing and excessive loss of water. y Prickles of some plants help in support e.g., Rose. 3. GROUND OR FUNDAMENTAL TISSUE SYSTEM y Derived from ground meristems and forms a Gray Matter Alert!!! major part of the plant body. y Includes all the tissues excluding epidermal and In some plants, the hairs are vascular tissues. glandular and secrete essential oil that provide characteristic The Ground Tissue System in Roots and Dicot odour to the plants e.g., Citrus. Stems The epidermis of some plants y Hypodermis bear stinging hair e.g., Urtica y Cortex (Stinging Nettle). y Endodermis y Pith y Medullary Ray The Ground Tissue System of Monocot Stems y Hypodermis y Ground Parenchyma The Ground Tissue System of Dicot Leaves (Mesophyll) It is differentiated into two types of photosynthetic tissues in dicot leaves y Palisade Parenchyma y Spongy Parenchyma Previous Year’s Question y In monocot leaves mesophyll is made up of same type of cells. Casparian strips occur in (1) Cortex 4. VASCULAR TISSUE SYSTEM. (2) Pericycle y Pericycle is a constituent of Vascular tissue (3) Epidermis Anatomy of Flowering Plants system and is the outermost layer of Vascular (4) Endodermis tissue cylinder. y The endodermal cells of roots possess strips or bands of thickening made up of suberin called casparian strips (Caspary, 1865). y Among the thick-walled endodermal cells, few small, thin-walled cells opposite to protoxylem are found. These are called passage cells, helpful in the passage of water from cortex to xylem. 25.  y This vascular tissue system is derived from procambium. y In higher plants (Gymnosperms and Angiosperms), the vascular tissue consists of distinct, small patches called vascular bundles prior to the secondary growth. y Each bundle is made up of xylem and phloem with cambium (in stems of Gymnosperms and Definition Angiosperms) or without cambium (in monocot stems) or only one kind of tissue-xylem or phloem Vascular bundle: Xylem and (in roots). phloem constitute a vascular bundle in plants. TYPES OF VASCULAR BUNDLES (a) Radial Vascular Bundle (In monocot and Dicot Roots) Radial vascular bundles are the most primitive type of vascular bundle. The xylem and phloem form separate bundles and lie on different radii. (b) Conjoint Vascular Bundle The vascular bundles which contain both xylem and phloem are called conjoint vascular bundles. In this type, xylem and phloem are arranged on the same radius. Previous Year’s Question Types of Conjoint Bundles: Collateral, Bi- Secondary growth does not occur Collateral and Concentric. in monocots as their vascular (i) Collateral bundles are - A conjoint bundle with xylem towards the inner (1) Radial side facing the pith and phloem towards the outer (2) Scattered side facing the cortex, is called collateral bundle. (3) Enclosed by sclerenchyma y Open Vascular Bundle: When in a collateral (4) Closed bundle, a strip of cambium is present between Anatomy of Flowering Plants xylem and phloem, the bundle is called open bundle, e.g., stems of Gymnosperms and most dicots. y Closed Vascular Bundle: When a collateral bundle is without a strip of cambium, it is said to be closed bundle, e.g., monocot stems. 26.  (ii) Bi-Collateral y When a conjoint bundle has phloem both on Previous Year’s Question the outer and inner side of xylem, usually a strip of cambium is present on both outer and inner Bicollateral bundles occur in stem sides of xylem. of __________. y Bicollateral bundles are characteristic of family (1) Dracaena Cucurbitaceae. (2) Pumpkin y They also occur in families Solanaceae, (3) Canna/gram Convolvulaceae etc. (4) Sunflower Anatomy of Flowering Plants 27.  (iii) Concentric y When one kind of vascular tissue (xylem or phloem) forms a solid core, while the other surrounds it completely on all sides, the vascular bundle is called concentric. y A strip of vascular cambium is always ABSENT in concentric bundles. Types of Concentric Bundles Previous Year’s Question Amphicribal (Hardocentric) y Xylem forms a central core, while phloem Amphivasal or leptocentric surrounds it on all sides. vascular bundles are found in y It occurs in some aquatic Angiosperms and __________. staminal bundles of anthers. (1) Cycas and Dryopteris Amphivasal (Leptocentric) (2) Dracaena and Yucca y Phloem forms a central core, while xylem (3) Helianthus and Cucurbita surrounds it on all sides. (4) Maize and wheat y It occurs in some aquatic angiosperms and staminal bundles of anthers. ANATOMY OF ROOT y Young Dicot Root (Primary Dicot Root) A young dicot root, which possesses only primary tissue is called primary dicot root. The primary internal structure of a dicot root can be studied from transverse section of a young root of gram. 1. Epiblema or Piliferous layer y It is the outermost layer of the root. Rack your Brain y It is made of completely arranged thin walled flattened and slightly elongated Sunflower plant is a dicot plant living cells. still it does not show secondary y It is typically uniseriate and lacks the growth. State the possible cuticle and stomata. reason. Anatomy of Flowering Plants y Some cells of the epiblema give rise to thin-walled tubular outgrowths called root hair. y Due to the presence of the root hair, epiblema is also known as piliferous layer (L. pilus-hair, ferse-to carry). y The root hair markedly increases the absorbing surface of root. 28.  y The root hair lies in between the soil particles and thus always remain in contact with the soil water. y Root hairs possess a gummy pectin layer on the outside for cementing with soil particles and retaining water on their surface. y The root hairs commonly live only for few days and die off in older parts of the root. y The older epiblema cells become suberised and cutinized. 2. Cortex y It is next to the epidermis consists of several layers of thin walled Parenchymatous cells with conspicuous intercellular spaces. y The cells of cortex store food. y Cortex also conducts water from the epiblema to the inner tissues. 3. Endodermis y It is the innermost layer of the cortex. y It is made up of a single layer of barrel-shaped cells which do not enclose intercellular spaces. The endodermal cells are living and are rich in starch grains. y They possess characteristic bands of thickening Definition along their radial and tangential walls. y These are called casparian bands or casparian Casparian Strips: The strips (after Caspary 1885.) endodermal cells of roots have y The casparian strips are made up of suberin and deposition of suberin and lignin lignin (Esau, 1965). on their radial and tangential y Casparian strips prevent plasmolysis of walls, forming a characteristic pattern of thickening called Anatomy of Flowering Plants endodermal cells and do not allow wall to wall movement of substance between cortex and casparian strips (after Caspary pericycle. 1885) y The cells of endodermis, laying opposite the 29.  protoxylem are thin-walled to permit free passage of water and minerals from cortex into Definition the xylem. These are called passage cells. Stele : The cells that lie in the 4. Stele centre of dicot stems, dicot y The world stele is derived from Greek language roots and monocot roots which means ‘Pillar’. constitute stele, it is bound by y All tissues inside the endodermis comprise the pericycle. stele. y In consists of pericycle, vascular bundles, pith and medullary rays (if present). y In seed plants i.e., Angiosperms and Gymnosperms, the stele is called eustele. y In eustele, the vascular bundles are arranged in one or more rings. y In monocot stems vascular bundles are scattered. Such a stele is a variant of eustele. (i) Pericycle y It lies inner to the endodermis and consists of thin-walled parenchyma cells. y It is generally uniseriate but may be multiseriate. y Pericycle forms the outer boundary of primary vascular cylinder. Previous Year’s Question y Pericycle is absent in the root of parasites and some aquatic plants. Endodermis is part of __________. y The pericycle is a very important layer (1) Epidermal system in the roots as all the lateral roots, cork (2) Interstellar tissue cambium and a part of vascular cambium (3) Extrastellar tissue arise from the pericycle. (4) Vascular tissue (ii) Vascular strand y It consists of separate bundles of xylem Anatomy of Flowering Plants and phloem arranged alternately inner to the pericycle. y Thus, the xylem and phloem bundles are equal in number and lie on different radii. Such vascular bundles are called radial bundles. y The number of xylem or phloem bundles 30.  may vary from two to six and very rarely up to eight. Definition y Based upon the number of xylem bundle, the root may be diarch (with two xylem bundles, e.g., tomato), triarch (with three Protoxylem is the first part of xylem bundles e.g., pea), tetrarch (with two the primary xylem that has xylem bundles, e.g., sunflower), pentarch xylem vessels of narrow lumen (with five xylem bundles) and polyarch (with more than five xylem bundles.). y Each xylem bundle consists of the first formed xylem-the protoxylem towards the periphery, and the later formed xylem- the metaxylem towards the centre of the root. Such a xylem is called exarch and is a characteristic of root. y The metaxylem elements of different bundles, meet in the centre to form a solid star-shaped structure. In such case, pith is absent (e.g., sunflower). y However, in some cases, the metaxylem elements of different xylem may lie separate from one another so that a small pith is present in the centre of the root (e.g., gram, bean). y Xylem elements appear polygonal in transverse section. Xylem conducts Definition water and mineral salts to the shoot and provides mechanical strength. Metaxylem differentiates after y Phloem consists of sieve tubes, companion protoxylem that has xylem cells and phloem parenchyma. vessels of broad lumen. y In some roots, each phloem bundle is provided with a few sclerenchyma cells towards the outer side. Anatomy of Flowering Plants y Phloem conducts organic food from shoot to the root along with its branches as well as to the upper parts too, so translocation of food is bidirectional. (iii) Pith y It is often absent. 31.  TYPES OF STELE IN PTERIDOPHYTES Previous Year’s Question Protostele Siphonostele or medullated stele Endodermis of dicot stem is also called ________. Ectophloic (1) Bundle sheath Haplostele (2) Starch sheath (3) Mesophyll Amphiphloic Actinostele (4) Water channel Equistelic siphonostele Plectostele Solenostele Mixed protostele Dictyostele Polycyclic stele y If present, the pith is quite small and made of parenchyma cells. y Intercellular spaces are absent, and the cells store food as well as waste materials. MONOCOT ROOT A transverse section of monocot root consists of following tissues from outside to the centre. 1. Epiblema or Piliferous layer y It is the outermost layer of thin-walled living cells. y It is typically unicellular in thickness and lacks the cuticle. y Some of its cells give rise to root hair. Anatomy of Flowering Plants y Root hairs have pectic layer on their outer surface to bind the soil particles and are also useful in water retention. y They take part in absorption of water and mineral salts. y In older part of the root, the root hair dies off and the epiblema becomes impervious. 32.  2. Cortex Definition y It lies inner to epiblema and consists of several layers of parenchymatous cells having Passage cells: Unsuberized cells intercellular spaces. in the endodermis of stem that y It is a much wider region. lie opposite to xylem strands. y In older roots, the outer few layers of cortex become thick walled and suberised. y They constitute the exodermis. y The cortical cells store food, conduct water and minerals from the root hair to the inner tissues. y The exodermis takes over the function of protection in older roots, when epiblema decays. (a) Endodermis y It is the innermost layer of cortex. y It is made up of compactly arranged barrel-shaped cells. y The young endodermal cells possess an internal strip of suberin, and lignin called as casparian strip. It soon becomes indistinguishable due to the additional thickening of the endodermal cells. y The endodermal cells opposite the protoxylem groups, remain thin walled and are called passage or transfusion cells. y They allow the conduction of the sap from the cortex to the inner tissues. Rack your Brain (b) Stele The tissues inside the endodermis constitute stele. These include pericycle, What is the term used for the circular strands and pith. waxy coating on the epidermis of (i) Pericycle young stem? y It is the outer boundary of vascular strand and lies below the endodermis. Anatomy of Flowering Plants Pericycle may be uniseriate (single layered, e.g. Maize) or multiseriate (multilayered, e.g., Smilax), and is composed of thin-walled parenchymatous cells. 33.  y In many older roots, some of the pericycle cells become thick-walled. y In monocot roots, the pericycle produces only lateral roots. (ii) Vascular strand Gray Matter Alert!!! y It consists of alternately arranged radial bundles of xylem and phloem. There is no distinction between y The number of these vascular bundles the internal structure of a young is quite large i.e., always eight or more. and old monocot root, since y Thus, the root is polyarch. The vascular secondary growth is absent in bundles are arranged around a large the monocot roots. central pith. y The xylem bundles are exarch i.e., protoxylem lies towards the outside and metaxylem face inwards. y Xylem is made up of rounded or oval vessels. y It provides mechanical strength and helps in the conduction of water and minerals. y The phloem bundles alternate with the xylem bundles. y The phloem and xylem bundles are separated from each other by means of parenchymatous or sclerenchymatous conjuctive tissue. y If cells of conjunctive tissue are parenchymatous, then it stores food. y If cells of conjuctive tissues are sclerenchymatous, then they provide mechanical s