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Lesson 9: Anatomy of Flowering Plants

Anatomy of Flowering Plants


The branch of Botany dealing with the internal organisation of the plants is called Anatomy. The foundation of Plant Anatomy was laid down by N.Grew. The term tissue was coined by him. He is called the 'Father of Anatomy'.

The Tissues:

A group of similar or dissimilar cells that perform a common function and have a common origin is called a tissue. Tissues are classified into two main groups: Meristematic and Permanant. 

(A) Meristematic Tissues:

1. These tissues consist of cells that retain the power of division.
2. The protoplasm within the cell is dense, the vacuole smaller or absent.
3. These cells are isodiametric  without intercellular spaces.
4.The nucleus is bigger in size.
5.The cells of the meristimatic tissues have thin cellulosic cell wall.
6. The cells are metabolically highly active with high surface area per unit volume and nucleo- cytoplasmic ratio.
7.Ergastic substances are absent.
8. Colourless protoplastids are present in the cells.

Clasiification of Meristems:

(1)  On the basis of origin and Development:

(i) Promeristems: ( primordial meristem) :  A group of cells which represent primary stages of meristamatic cells. They are found at the apices of embryonic roots and shoots. They give rise to primary meristems.

(ii)  Primary meristems: They originate from promeristems . Found at shoot and root apices, at the apex of leaves and intercalary parts.They give rise to primary permanent tissue.

(iii) Secondary meristems: They are not present from the beginning  of the formation of an organ but develop at a later stage.They give rise to secondary permanent tissues. e.g interfascicular cambium , cork, and cambium in dicots.

(2) On the Basis of Position:

(i) Apical Meristem: These cells or tissues are found at the apices of stem and root.Due to continues division the root and stem increase in length. The apical meristem help the plants to grow in length.

(ii) Intercalary meristem: The tissues are intercalated between permanent tissues. These are  actually the part of the apical meristem which gets separated from it during the growth of stem and root in length. e.g. Stem of grasses, Equisetum. They are especially responsible for increase in the length of the stems of grasses.

(iii) Lateral Meristem: These meristems are present along the lateral side of stem and roots.They divide in tangential plane , giving rise to the secondary permanent tissues on the inner and outer side and lead to the increase in thickness of girth, of the plant body 

e.g. Intrafascicular cambium, interfascicular cambium and cork cambium.

(3)On the basis of Plane of Cell Division:

(i) Mass Meristem: The cells divide anticlinally in all planes, so that mass of cells is formed. e.g. Formation of spores, cortex, pith, endosperm.

(ii) Plate Meristem: The cells divide anticlinally in two planes, so plate like area is increased. e.g. Formation of epidermis and lamina of leaves.

(iii) Rib or File Meristem: The cells divide anticlinally in one plane , so row or colums of cells is formed e.g. Formation of a lateral root.

(4) On the basis of Function : 

(i) Protoderm: They are the outermost meristematic cells. They form skin or epidermis of plant and epidermal tissue system.

(ii) Procambium: They are the innermost meristematic cells. They form primary xylem, primary phloem, and cambium.

(iii) Ground meristem:  They form ground or fundamental tissue such as hypodermis, cortex, pith, pericycle etc.

Shoot Apex Organisation:

The shoot Apex is present immediately above the youngest leaf primordia. It consists of meristematic cells . Lateral branches of stem and leaves are formed by the activity of shoot apex such as:.

(i) Apical cell theory: It was proposed by Holfmeister and Nageli. According to this theory a single apical cell leads to the development of entire plant body. This theory is applicable to algae, to most of the bryophytes and pteridophytes.

(ii) Histogen theory: It was proposed by Hanstein. According to this theory , shoot apex consist of following histogens:

(a) Dermatogen: Outermost layer. It forms epidermis ( skin) and epidermal tissue system.
(b) Periblem: It gives rise to the tissues between epidermis and stele.
(c) Plerome: Innermost layer. The central mass of cells which gives rise to central stele.



                                                           Source:shikshaservices.com

(iii) Tunica Corpus theory : It was proposed by Schmidt (1924) It  is based on plane of division of cells . According to this theory, shoot apex consists of two distinct layers as: 

(a) Tunica :  It is mostly single layered and forms epidermis. The cells of tunica are smaller than corpus  and  divide mostly by anticlinal divisions.

(b) Corpus: It  represents central core with larger cells.The cells divide periclinally. Sometimes tunica is multilayered , only outer layer forms epidermis  and the remaining layers with corpus form cortex of shoot.

Root Apex Organisation:

Root apex consists of mass of meristematic cells. Root apex is not resposible for the formation of lateral roots. Root cap or calyptrogen  is present due to which root meristem becomes subterminal in position.  If  root  cap is independent in origin  it arises from the dematogen.

Regarding the organisation of root apex, following theories have been put forward.

(i) Korper-kappe theory: It was proposed by Schuepp: (1917) : This theory is comparable with the tunicacorpus theory of shoot apex , Korper means body and kappe means cap.

(ii) Quiescent center theory: It was proposed by Clowes (1956-58) . According to this theory root apex consist of an inverted cup like structure , the quiescent center. The cells of this region have  very  low mitotic activity (quiescent). They have low amount of RNA, DNA, and protein. They are surounded by layer of actively dividing cells which is responsible for formation of different structures of roots.

(B) Permanant tissue:

They are composed of living or dead cells which are derived from the meristematic tissue but have lost their ability to divide. These are of three types:

(i) Simple tissue:

They are made up of one kind of cells performing similar function.

(a) Parenchyma (Grew ) These cells are found almost in all parts of plants such as roots, stem, leaves, fruits and seeds. These cells are isodiametric , spherical, oval or polygonal with intercellular spaces. These cells are living and within cellulosic cell wall.

Types:

(a)  Prosenchyma: Elongated parenchyma with tapering ends is called prosenchyma.
(b) Aerenchyma: The parenchyma which encloses air cavity is called aerenchyma ( hydrophytes).
(c) Chlorenchyma: The parenchyma containing chloroplasts is called chlorenchyma.
(d) Idioblast: Sometimes they store secretory substances (  ergastric substances) such as tannins , resins, and gum and they called idioblasts.
(e) Storage parenchyma : Fruits , endosperm.

(b) Collenchyma: ( Schleiden) These cells have thickenings on the cell wall and in corners of intercellular  spaces. They are not found in roots and monocots. These cells form the hypodermis in stem and petiole. It is living mechanical tissue with high refractive index. The thickening material in the cell wall contains pectocellulose.

Colenchyma is of three types:

1. Angular Collenchyma: Dposition of hemicellulose and pectin occurs only in the angles between the cells. Angular walls thickened e.g. Stem of marigold and tomato.

2.Lamellar collenchyma: Deposition of hemicellulose and pectin occurs only at the crosswalls separating the adjacent cells. Tangential walls thickened e.g  stem of Sunflower.




                         Types of Collenchyma. Source: tutorvista.com



3. Lacunate collenchyma: The deposition of hemicellulose and pectin occurs only along the border of intercellular spaces. Lacunate thickening , intercellular spaces are present  e.g. Stem  of cucurbita.

Function: They provide mechanical support , flexiblity  and elasticity to the organs  and due to peripheral position in stems they resist bending and pulling action of wind. It is especially useful for young plants and herbaceous organs where it is an important supporting tissue.

(c) Sclerenchyma:  ( Mettenius)  These cells have thickened secondary walls due to deposition of lignin At maturity they die. These cells have simple pits. They are of two types:

(i) Sclerids: They may be spherical , oval and cylindrical . They are lignified , extremely thick walled. The lumen of the cells is almost obliterated. They are found in the hard parts of the plants.


          


            


                                                 Source:studentsguide.in


A: Brachsclereids  B: Astrosclereids  C  & D : Macrosclereids E: Osteosclereid F:  Trichosclereid

Types of sclereids:

1. Brachysclereids ( Stone cells) :Grittiness in friuts is due to stone cells . e.g. Pear, Sapota.
2. Macrosclereids ( Rod cells) : Found  in seed coat of leguminous plants.
3. Osteosclereids (Prop cells): Found in leaves and seed coat of  many monocots and subepidermis of legume seed coats.
4. Astrosclereids (star cells) They are common in stem and leaves of dicots . e.g. Tea leaves. Petiole of lotus.
5. Trichosclereids ( internal hair) Long hair like branched sclereids. They are common in hydrophytes. These are also present in the aerial roots  of Monstera and Olive leaves.

(ii) Sclerenchymous fibres: They are long and tapering at the ends. These are thick walled cells which are lignified. The fully developed fiber cells are always dead. The length of fiber varies from 2-550mm in angiosperms and 1-12mm in gymnosperms. The fibres are present in hypodermis of monocot stem , in pericycle of many dicots, in secondary wood and in vascular bundle sheath in monocot stems e.g. Jute, Flax, Hemp. Living fibres are found in Tamarix.

Function: The main function of sclrenchyma  to provide mechanical strength.

Complex tissues:

Made up of different types of cells. They include xylem and phloem.

(A) Xylem:  (Nageli) or hadrome ( Haberlandt):  It is chief water conducting element. Xylem consists of following types of cells.

(i) Tracheids: They are elongated cells with pointed chisel like ends. Their wall is tough , thickened, lignified and thickening may be annular, spiral, reticulate, scariform or pitted. Cells are dead at maturity and have bordered pits. In pteridophytes and tracheids are associated with vessels. The main function is conduction of water. The tracheids are most primitive type of conducting elements in xylem.

(ii) Vessels: They are also elongated tube like, formed from a row of cells placed end. The partition walls are either perforated or disappear altogether resulting in an elongated tube. Walls thickened , lignified, may have annular, spiral, reticulate or scalariform thickening. Vessels are dead at maturity and without nuclei. In pteridophytes and gymnosperms vessels are absent ( Non- porous wood). Sometimes primitive vessels are present in Gnetum and Ephedra ( Gnetales). Vessels are characteristic of angiosperms (Porous wood) . Vesselless angiospermic families  are Tetracentraceae, Trochodendraceae, Winteraceae. The  main function is conduction of water . Vessels are advanced type of conducting elements.

On the basis of distribution and size of vessels porous wood is of two types:

a) Diffuse porous wood ( primitive): Vessels of same size are uniformly distributed through out the growth e.g. Pyrus, Betula.

b) Ring porous wood ( advanced) : Large vessels are formed in early wood when the need of water is great and small vessels are formed in late wood e.g. Quercus, Morus.

(iii) Wood or xylem fiber: These cells are elongated and pointed at both the ends. Cell wall is highly lignified having simple pits. They are commonly found in scondary xylem. They may be of the folowing types.

a) Fiber tracheids: Fiber like tracheids with bordered pit.

b) Libriform fiber: They have extremely thick walls and simple pits. They provide mechanical support.

(iv) Wood or xylem parenchyma: They are living parenchymatous cells associated with xylem.They may occur as axial parenchyma or ray parenchyma. When the parenchyma ois diffused or not associated with vessels, they are known as apotracheal parenchyma. And when parenchyma surrounds or is associated with vessels , they are called as paratracheal parenchyma.

On the basis of origin , xylem is of two types:

(i) Primary xylem: It is derived from procambium during the formation of primary plant body. It is differentiated into protoxylem ( first formed and consist of tracheary elements and xylem parenchyma) and metaxylem.( later formed and consists of tracheary elements, aylem parenchyma and fiber.) The cells of metaxylem are bigger in size than protoxylem.

(ii) Secondary xylem: It is formed from cambium during secondary growth. It is well dierentiated into two systems.

(a) Axial or vertical system:

(i) Teracheary elements ( Tracheids and vessels) for conduction of water.

(ii) Xylem or wood fiber- for support

(iii) Xylem parenchyma ( for storage of food)

(b) Ray or Horizontal system:

Ray parenchyma: for storage of food.

(B) Phloem or bast or Leptome ( Haberlandt) : Phloem consists of following types of cells.

(i) Sieve element: The sieve elements in angiosperms are sieve tubes which are cylindrical tube like cells with perforated cross walls called sieve plate. Sieve tubes are associated with companion cells and they are without nuclei. In pteridophytes and gymnosperms the sieve elements have sieve plates on their lateral walls  and companion cells are absent. They are called as sieve cells.  The walls of the sieve tube elements are made up of cellulose and pectic substances. The cytoplasm is confined to a thin peripheral layer. P-Proteins are proteinaceous structures present in sieve tubes and are believed to be responsible for (i) movement of materials and

(ii) sealing of pores after wounding. 

At the end of growing season, the old sieve tubes, a callose plug  whcih is made up of callose carbohydrate  is deposited in sieve plate  which inhibits the activity of sieve tubes. In spring season, the callose plug gets dissolved.

(ii) Companion cells: They are elongated living parenchymatous thin walled cells. They are associated laterally to sieve tubes  and have dense cytoplasm and nuclei. Companion cells are absent in Pteridophytes and Gymnosperms. Both sieve tubes and companion cells are related ontogenetically since both develop from the same mother cell.  They are the sister cells. 

(iii) Phloem or bast fiber: These are absent or very few in phloem  and abundantly found in secondary phloem.  They are schlerenchymatous fibres associated with phloem. Phloem fibers of plants like Jute, flax, and hemp are retted in water and extracted for making ropes and coarse textiles.

(iv)  Phloem parenchyma:  They are  parenchymatous living cells with cellulosic cell wall and nucleus. The main function is storage of food. They are not found in monocotyledonous plants.

Types of Phloem:

(A) On the basis of position:

(i) External phloem: The phloem is of normal type and is present outside the xylem. e.g. Mostly angiosperms and gymnosperms.

(ii) Internal or Intraxylary Phloem: It originates from procambium  and is the primary phloem  which  occurs on innerside of primary xylem in bicollateral bundles. e.g. Members of Apocynaceae, Asclepiadaceae, Convovulaceae, Solanaceae.

(iii) Included or Interxylary phloem: It originates from cambium and is secondary phloem which occurs in groups within the secondary xylem e.g. Savadora, Amaranthus, Chenopodium etc.

(B) On the basis of Origin:

(i) Primary Phloem: It develops from procambium. It does not have radial differentiation.  Or rays are absent.  It is differentiated into protophloem  ( consists of sieve elements  and parenchyma) and metaphloem  ( develops after protophloem and consists of sieve elements, parenchyma and fiber).

During the primary growth  the protophloem elements  are crushed by the surrounding tissues and disappear . This process is termed as obiliteration.

(ii) Secondary Phloem:  It develops from the cambium during secondary growth.  It showa radial differentiation. It consists of two ditinct systems  such as :

a) Axial or vertical System:

(i) Sieve elements: Sieve tube and Companion cells. For the conduction of food .
(ii) Bast fiber: For support.
(iii) Bast Parenchyma: For storage of food.

(b) Ray or horizontal system

(i) Ray parenchyma : It is for the storage of food.

(3) Secretory Tissues:

Special modifications of secretory tissues : These tissues are of two types:

(a) Laticiferous tissues : They contain colourless, milky or yellow coloured juice called  larex. These tissues are of two types:

(i) Latex cells: They do not fuse and do not form network. Plants having such tissues are called simple or non- articulated laticifers e.g. Calotropis ( Asclepiadaceae) , Nerium , Vinca ( Apocyanaceae), Euphorbia ( Euphorbiaceae) Ficus ( Moraceae).

(ii) Latex vessels: They are formed due to fusion of cells and form network like structure. Plants having such tissues are called compound or articulated laticifers e.g. Argemone, Papaver ( Papaveraceae) Sonchus ( Compositae) Hevea, Manihot ( Euphorbiaceae).

(b) Glandular tissues:  They include different types of glands which secrete oils, gums, mucilage, tannins and resins. They may be:

(i) External glands: Present as epidermal outgrowths.

Types:

1. Glandular hair:  With a stalk and head e.g. Tobacco,Plumbago, Boerhaavia.

2. Stinging hair : Sereste poisonous substance e.g. Urtica.

3. Nectaries: Sccrete sugary substance , may be extrafloral present on the stem, leaves etc. e.g. Nepenthes, Catheranthus or floral e.g.  Corchorus, Thea, Polygonum, Jatropha.

4. Digestive Glands: Present in Insectivoruos plnts. e.g. Drosera, Nepanthes, etc.

(ii) Internal Glands :

(1) Oil Glands: Present in the mesophyll of leaves and cortex of stem fruit  e.g. Orange, Lemon etc.

(2) Mucilage secreting glands: e.g. Leaves of Piper betel.

(3) Gum, tanin, and resin secreting glands or ducts present in gymnosperms  and angiosperms e.g. Pinus. Resin ducts are scizogenous in origin.

THE TISSUE SYSTEM

The plant body consists of thre major tissue systems.namely:

(A) Epidermal tissue sytem:  It consists of epidermis and its associated structure like hairs, trichomes, cuticle, stomata, and bulliform cells. The epidermis is mostly single layered parenchymous but multilayered in Ficus, Nerium. Epidermis is mainly protective in nature. In grasses, motor or bulliform cells are present in upper epidermis. In grasses and Equisetum , silica is present in th epidermal cells. The epidermal cells containing cystoliths are called as lithocycts.

(B) Ground or fundamental Tissue system: It extends from th epidermis to the center of axis.  Excluding  the vascular tissue. The ground tissue constitute of  the following parts:

(i) Cortex: It lies between the epidermis and the pericycle. It is further differentiated into :

(a) Hypodermis: It is collenchymatous in dicot stem and sclerenchymatous in monocot stem. It provides strength.

(b) General cortex: It consists of parenchymatous cells. The  main function is the storage of food.

(c) Endodermis: ( Starch sheath) Mostly single layered and is made up of parechymatous barrel shaped compactly arranged cells.

The inner and radial walls of endodermal cells have casparian strips. In roots thick walled endodermal cells are interrupted by thin walled cells just outside the protoxylem patches. The thin walled endodermal cells are called passage cells.

This endodermis checks the water loss and entry of air in xylem elements.

(ii) Pericycle: It lies between the endodermis and vascular tissue. It is parenchymatous in roots and sclerenchymatous or mixed with  parenchyma in stem. The pericycle cells just opposite the protoxylem are the seat of origin of lateral roots. In dicot roots, pericycle form part of cambium or whole of cork cambium.

(iii) Pith: It occupies the central part in dicot stem and monocot root. Mostly comprised of parenchymatous cells. In dicot root , pith is completely obliterated by the metaxylem elements. In dicot stem the pith cells between the vascular bundles become radially elongated and are known as primary medullary rays or pith rays. They help in lateral translocation.

(C)  vascular tissue system:

The vascular bundles found in steler part constitute vascular tissue system. Xylem, phloem and cambium are the major part of the vascular bundle. Vascular bundles may be of the following types:

1) radia: When the xylem and the phloem are arranged on different radii alternating with each other e.g. Roots.

2) Conjoint: When xylem and phloem combine in the same bundles and are present on the same radius e.g. Stem.  Conjoint vascular bundles may be:

a) Collateral: Xylem is towards innerside and phloem toward the outerside.

(i) Open:       Cambium is present between xylem  and phloem . e.g. Dicot stem.
(ii) Closed:   Cambium is absent between xylem and phloem e.g. Monocot stem.

b)Bicollateral : When xylem has cambium and phloem on both side e.g. members  of Cucurbitaceae, Solanaceae, Apocyanaceae.

3. Concentric: When  one vascular tissue surround the other . They are of two types:

(a) Amphicribal or Hadrocentric: The xylem is surrounded on  all sides by phloem e.g. ferns.

(b)Amphivasal or Leptocentric: The Phloem is surrounded on all sides by xylem e.g. Yucca, Dracaena.

                                     

  Collateral closed                                     Bicollateral           Collateral open



                                                         

Amphivasal                          Amphicibral                                   Radial


Different Types of vascular bundles. Source:www.studentsguide.in

INTERNAL STRUCTURE OF DICOT AND MONOCOT PLANTS

Anatomy of root: The three zones that can be distinguished in a root are:

(i) Epidermis:  (Epiblema /Rhizodermis) : It is single layered ( uniseriate) and consists of tightly placed , thin walled uncutinised cells.

This epidermis layer is called as epiblema, piliferous layer or rhizodermis. Epiblema in younger roots bears unicellular root hairs ( water absorbing organs).

(ii) Cortex: It consists of thin walled parencymatous cells with intercellular spaces. In most monocots  and some dicots cortex layer below epidermis becomes suberised to form protective tissue called exodermis. The cells of cortex store food material ( e.g. Carrot). The inner most layer of cortex develops  into endodermis. It is made up of closely packed living cells characterized by the presence of band like thickening; made up of lignin and suberin on their radial and transverse walls. These bands or strips are called casparian bands or strips . Some cells of endodermis lying opposite to protoxylem remain thin walled and are called passage cells which allow radial diffusion of water.

(iii)Vascular bundles: Vascular bundles are radial and exarch. The center of monocot root is occupied by parenchymatous cells called pith.

Difference between dicot and monocot root





           


                   


                 T.S of Monocot Root                                              T.S. Of Dicot Root

                                     Source : tutorvista.com

Anatomy of stem:

1.Primary structure of Dicot stem:

Dicot stem consists of following layers:

(i) Epidermis: It is the outermost layer consisting of single layer of closely arranged cells with cuticle. It bears multicellular hairs.

(ii) Cortex: It is differentiated into hypodermis , general cortex, and endodermis. Hypodermis is collenchymatous. General cortex bundles consisting of phloem and xylem.

(iii) Vascular bundles: Vascular bundles are conjoint , collateral or bicolateral, open and endarch and are arranged in ring. ( Eustele).

(iv) pith: It is the central portion of stem consisting of parenchymatous cells with narrow radially elongated parenchymatous cells extend from pith toward the periphery are called medullary rays. The main function is food storage.

2. Primary structure of monocot stem:

Monocot stem consists of following layers:

(i) Epidermis: It is the outermost layer and consists of sompactly arranged parenchyma cells which are usually covered with cuticle.

(ii) Hypodermis : cells of hypodermis are sclerenchymatous  providing mechanical strength to the stem.

(iii) Ground tissue: All the tissue internal to hypodermis represents the ground tissue. It is made up of parenchymatous cells rich in food reserve like starch.

                   
     T.S of Monocot Stem                                                                         T.S. Of Dicot Stem


                                             Source: tutorvista.com


(iv)vascular bundles: they lie scattered in the ground tissue. Each vascular bundle is surrounded by 2-3 layered sclerenchymatous sheath . The vascular bundles are conjoint, collateral, closed and endarch (Atachostele) Vessels arranged in V shaped manner. Schizolysigenous water canals are present below the protoxylem.


                                Difference between dicot stem and monocot stem





Anatomy of Leaf:

Structure of dorsiventral leaf ( Dicot) :

In the cross section of a leaf the following parts can be seen:

(i) Epidermis: The upper and lower surfaces are covered by the epidermis. Cells of epidermis are parenchymatous and are closely packed together without any intercellular spaces.  Mostly the stomata are restricted to lower surface of the leaf which is known as hypostomatic. The outer walls of the epidermal cells are thickened  and cutinized which prevents the loss of water.

(ii) Mesophyll : In between the two epidermal  layers , there are numerous chlorenchyma cells which constitute the mesophyll. In dicots there are two distinct layers of mesophyll the palisade ( upper layer consisting of closely arranged column shaped cells containing abundant chloroplasts). And spongy tissue ( the lower layer of irregularly shaped cells containing fewer chloroplasts.)

(iii) Vascular bundles: Vascular bundles in the leaf are located in the mid rib and the veins. Vascular bundles are conjoint, collateral, and closed. Bundles are surrounded by a compact layer of parenchymatous cells which is called a bundle sheath. The xylem ( protoxylem) is toward upper epidermis ( adaxial) and the phloem on the lower side (abaxial).





1. Upper Epidermis 2. Cuticle  3. Polisade Parenchyma   4 Sclerenchyma 5. Xylem 6. Border Parenchyma 7. Lower Epidermis 8. Phloem 9. Spongy Parenchyma 10. Stama 12. Respiratary Cavity.
                                                    
Source: student'sguide.in


Structure of  isobilateral leaf ( Monocot)

The monocot leaf is differentitated into three types of tissues:

(i) Epidermis : It consists of upper and lower  and lower epidermis, both of which may be interrupted by equal number of stomata. 

Both the epidermal layers are cutinized . In some grasses e.g. Poa, Agropyron,Psamma grass epidermal cells are large with thin flexible walls which are called as motor or bulliform cells. These cells help in the rolling of leaves.

(ii)  Mesophyll: Mesophyll cells are not differentiated into pallisade and spongy parenchyma. Mesophyll cells are made up of parenchyma cells which have chloroplasts.

(iii) vascular bundles: They are arranged in parallel manner. Vascular bundles are conjoint , collateral, closed and enclosed by a bundle sheath.  The xylem is towards the uper side ( adaxial surface) and phloem on the lower side ( abaxial surface)





                                                                V.S Monocot Isobilateral Leaf
                                                                source: studentsguide.in

1. Xylem                     6. Bulliform Cell
2. Phloem                   7. Upper Epidermis
3. Sclerenchyma         8. Bundle Sheath
4. Stama                     9. Vascular Bundle
5. Sub Stomatal Chamber     10. Mesophyll Tissue
11. Lower Epidermis


 Secondary Growth:  Increase  in girth or thickness or diameter of the axis due to formation  of new tissues as a result of joint activity of vascular cambium and  extrasteler region respectively. It occurs in the root and stem of gymnosperm and dicots.Secondary growth in dicot stemcompletes in the following steps:

A. Formation of vascular cambium ring:

(i) Intrafascicular cambium: It is primary in origin , present in between primary phloem and primary xylem.
(ii) Interfascicular cambium:  It is true secondary meristem. It originates from the  parenchyma cells of medullary rays region. It lies in between the vascular bundles .
(iii) Vascular cambium ring: Both intrafascicular and interfascicular cambium joins together and forms cambium ring.
Cells of cambium are of two types:
(a) Fusiform initials: They form tracheids, vessels, fibres and axial parenchyma in secondary xylem  and sieve tubes, companion cells , fibres and axial parenchyma in secondary phloem.
(b) Ray initials: These are isodiametric and form ray parenchyma and vascular rays.
(iv) Periclinical division of vascular cambium ring.
(v) Formation of sceondary phloem  ( outside the vascular cambium) and secondary xylem produced is 8-10 times grater than secondary phloem.
(vi) Fate of primary phloem and primary xylem being dead and lignified , replaced in the pith region.


                                                      
                       
                         Stages of Secondary Growth in a Typical Dicotyledons Stem
                                             source:.inplantphys.info

(vii) Formation of secondary structures i.e. Annual rings: sapwood and heartwood, hardwood and softwood etc.

(a) Annual rings: These are formed by the seasonal activity of vascular cambium. Cambium is not active through out the year. During the summer season or spring the cambium is more active and form large sized xylem elements ( vessels)  and constitue autumn wood or late wood. Both autumn and spring wood constitue a growth or annual ring. In a year only one growth ring is formed. In successive years numerous growth rings are formed. Counting the annual rings in the main stem it is easy to ascertain the age of the tree. This branch of science is known as Dendrochronology.

Growth rings are distinct or sharply demarcated in the plants of temperate climate e.g. Shimla, Nainital, Mussourie, due to presence of contrasting seasonal variations. Growth rings are not distinct or sharply demarcated in the trees of troical climate ( near equator) e,g, Clcutta, Bombay, madras due to absence of contrasting seasonal variations.

(b) Heart wood and sap wood: The young elements of secondary xylem in the peripheral region constitute sap wood or alburnum. It is physiologically active and light in colour.  The water conduction takes place through sap wood.
Sap wood is converted into heart wood or duramen in the central region. It is darker in colour due to deposition of tannins, gums, resins and physiologically inactive ( dead) and provides only mechanical support. During the conversion of sap wood into heart wood the most important change is development of tyloses in the heart wood. Tyloses are balloon like  structures develop from xylem parenchyma. These tyloses block the passage of xylem vessels so also called as tracheal plug. The heart wood is commercially used as wood. When the plant is made hollow , it will not die because the water conduction takes place through sap wood. The heart wood is well developed in Morus alba ( Mulberry) The heart wood is absent in Populus and salix palnt. The wood of Tectona grandis is termite resistant. As a tree grows lder thickness of heartwood increases and sap wood remains the same.
Heart wood is much more durable and resistant to microorganisms , insects and pests etc than sap wood. Wood of dicot trees is called porous or hard wood because it consists of vessels( pores). The wood of gymnosperms do not contain vessels ( pores) and is known as soft or non- porous wood. Such wood consists of 90-95% tracheids and 5-10% of ray cells. Sap wood will decay faster if exposed freely to the air.

B. Formation of cork cambium:

Cork cambium or phellogen develops from outer layer of cortex. It produces secondary cortex or phelloderm on innerside and cork or phellem on the outer side. The cells of phellem are dead, suberized and pimpervious to water. Cork cells are airtight and used as bottle stopper or cork. The bottle cork is prepared from the cork of Quercus suber  ( Oak tree). Cells of phelloderm are thin walled , living and store food. Phellem , Phellogen and phelloderm are collctively called periderm. Periderm is secondary protective tissue.

Due to pressure of secondary xylem , epidermis ruptures and cortex is largely lost after two or three years of secondary growth. In the cork layer ( bark) the lenticels are present which re meant for gaseous exchange.  In cork, lenticels have loosely arranged cells called complementary cells with intercellular spaces. For bottle corks the cork is processed in such a manner so that lenticels come in vertical direction.



                                                



   Begining of Lenticel Formation under a Stoma                                           Mature Lenticel                                        f –

Epidermis     
a - Epidermis
g – Stoma                                                 b - Complementary Cells
h - Complementary Cells                            c. Phellogen
d - Phellem


Bark includes all the dead and living tissues outside the vascular cambium. It may be:

(i)Scaly bark: When develops in strips e.g. Eucalyptus, Psidium.

(ii) Ring bark: When develops in the form of sheet or ring e.g. Betula ( Bhojpatra)

The outermost layer of bark is dead and is called as rhytidome.

In the ancient times the bark of betula was used as paper for writing the manuscripts.

Secondary Growth in Dicot Root:

Vascular bundles in dicot root are radial , exarch and mostly triarch. Vascular cambium is formed secondary from conjuctive parenchyma  cells lying just below each phloem strands. The number of cambium strips formed equals the number of phloem strands. The cells of pericycle lying outside the protoxylem also becomes meristematic to form part of strips of cambium. These cambial strips join the first formed cambium strips to form complete but wavy ring of vascular cambium. This cambium ring produces secondary xylem on inner side and secondary phloem on outer side. In roots, the growth rings are not distinct because there is no seasonal variation under the soil. From the outer layers of pericycle arises the phellogen which cuts phellem ( cork ) on the outer side and secondary cortex or phelloderm toward the innerside.



                        St ages of Secondary Growth in a Typical Dicotyledons Root

Lesson 8: Morphology of Flowering Plants

Morphology of Flowering Plants

Morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features.

The word "morphology" is from the Greek  word, study, research. The biological concept of morphology was developed by Johann Wolfgang von Goethe (1790) and independently by the German anatomist and physiologist   Karl Friedrich Budrach (1800).

Plant morphology deals with forms and features of different plant organs like roots, stems, leaves, flowers, seeds, fruits etc. The body of flowering plant can be divided into two fundamental partsi.e an underground root system and and an above ground shoot system. The root system grows downward into the soil and anchors the plant family  in the soil and absorbs water and various dissoved minerals from it.  The shoot supports foliage leaves and helps in conduction of water  and mineral substances from the soil and food material.

Life Span:

The plants may be:

a) Annual: life cycle is completed in one season or few weeks or few months e.g. Wheat, Maize, Euphorbia prostata.

b) Biennials: Life cycle is completed in two seasons; the vegetative growth occurs in the first season and the food is stored while reproduction occurs in the second season e.g. Henbane.The examples are Raddish, Carrot and Turnip are biennial in colder areas and  and annuals in the warmer areas.

c) Perrenials:  The plants live for  few to  many years and bear flowers and fruits every year (polycarpic). Bamboo ( Bambusa tulda) and Agave are monocarpic i.e. Flowering occurs only once at a time.

Habit of Plants:

1.   Herb: Stem is soft; less than 2m in height. e.g. Thyme, parsly, rosemary, mint.

2. Shrub: Perennial woody stem with medium height , trunk is absent e.g. Capparis Rosa, Bougainvillas    etc.  

3. Trees:  The stem is woody, the height is tall, stem is called trunk. The unbranched stem is called caudexor columnar eg Palm,

Magnifera indica.    An erect stem with swollwn nodes is called Culm e.g. Bamboos.

Excurrent: Lateral branches of trunk do not compete with the stem. e.g. Pinus, Casuarina, Eucalyptus.

Deliquescent: Main stem of trunk disappears after sometime and crown is dome shaped  e.g. Dalbergia , Ficus benghalensis.

A.Root

From the radicle of seed the root develops.  They are nongreen in colour, underground, positively geotropic, and  negatively phototrophic. They do not bear buds , but the buds are present for vegetative propagation in Sweet Potato ( Ipomoea)   and Indian red wood (Dalbergia) . Nodes and iInternodes are not present in the roots.  They have unicellular root hair.  Lateral roots arise endogenously i.e. From pericycle.

Types of Roots

Roots  develop from  radicle of seed. They are non-green underground , positively  geotropic and negatively phototropic.

Roots usually do not bear buds . But the buds are present for vegetative propagation in Sweet Potato(Ipomoea) and Indian red wood (Dalbergia). They do not bear nodes and internodes.  They have unicellular root hair. Lateral roots arise endogenously. i.e from the pericycle.

Types of Roots:

The roots are of three types:

(a) Tap Root: They develop from radicle. The primary root grows and gives rise to secondary  and tertiary tap root system. e.g. Dicots.They are large and fleshy in appearance.  Tap roots grow deep into the ground to search for food. are able to store food, which is particularly necessary for perennial plants during periods of dormancy.

(b) Fibrous roots: They lie close to the surface of the soil. They collect precipitation before it sinks deep into the ground. Fibrous roots can often be found growing side by side with taproots. In this condition the two roots combine tp provide maximum efficiency.They are mostly found in plants with one seed-leaf (monocots).

(c) Adventitious roots: They develop from any part of the plant body othet than the radicle . e.g. Monocots. They are shallo surface feeders like fibrous roots of grasses.develop to help the plant climb: for example, ivies.  help develop modified underground stems, such as bulbs . Adventitious roots are common in both dicot and monocot.

Parts of Roots:

(i) Root cap: the root cap is present at the apex of the root. It is smooth. It acts as a protective covering to the root. Multiple root covering is found in aerial roots of screwpine  ( Pandanus). In hydrophytes  root cap is either absent or replaced by root pocket e.g.  Pistia, Lemna, Eichhornia.

(ii) Zone of cell formation or division: The cells of this region are in an active state of division and their number increases continuosly. Vacuoles , neither small or big are present.  It may be a few  millimeters long.

(iii) Zone of cell elongation: Maximum growth in the cells occur in this zone. A large central vaculoe is present.

(iv) Zone of cell maturation: The cells are differentiated into permanant tissues depnding  upon   the functions  they have to perform.  The root hairs are also present in this zone.  In hydrophytes the root hairs are absent because they absorb water throughh general body surface. 

(1) Modification  of Tap root system:

(a)  storage / Fleshy roots:

1) Fusiform: e.g. Radish (Raphanus sativus)

2) Conical: e.g. Carrot (Daucus carota)

3) Napiform e.g. Turnip ( Brassica Napa), Beet Root ( Beta vulgaris)

4) Tuberous or Tubercular e.g. Mirabilis

(b) Respiratory Root (Pneumatophores) e.g. Avicennia, Sonneratia

(c) Nodulated roots e.g. Pisum sativum, Cicer arietinum.

(2) Modification  of Adventitious  root system:

(a)Storage Roots:

1) Tuberous e.g. Sweet Potato (Ipomoea batatas)

2) Fasciculated e.g. Asparagus, Dahelia.

3) Palmate e.g. Orchis

4) Nodulose .g. Mango ginger (Curcuma amada)

5) Beaded or moniliform e.g. Portulaca, Momordica

6) Annulated e.g. Ipecac (Psychortia)

(b)  Adventitious roots providing extra support:

(i) Prop roots: e.g. Old Banyan tree. ( Ficus  bengahalensis)

(ii) Stilt roots: e.g. Sugarcane, maize

(iii) Climbing roots: e.g.Porthos, Piper

(iv) Buttress roots: e.g. Bombax

(3) Adventitious roots with special function

(i) Respiratory roots: e.g. Jussiaea.

(ii) Assimilatory roots e.g. Tinospora, Trapa

(iii) Haustoria e.g. Cuscuta

(iv) Hygroscopic roots: e.g. Orchids

(v) Contractile roots: e.g. Saffron ( Crocus) Freesia

(vi) Root thorns: e.g. Porthos armatus, Acanthorhiza

(vii) Foliar/ Epiphyllous/ leafroots e.g. Bryophyllum, Bigonia, Salvinia

B. Stem

The stem is formed by the prolongation of the plumule of the embryo. The stem is positively phototropic and negatively geotropic and hydrotropic. The stem bears nodes  and internodes. The leaf bearing part is called shoot . It has buds.  Bud is condensed immature or embryonic shoot having a growing point surrounded by immature leaves. Cabbage is largest bud. 

According to nature: buds can be:

1) Vegetative -  form leafy shoots

2) Floral-  form flowers

3) Mixed – form both vegetative and floral characters

According to position , buds can be lateral or terminal.

Lateralbuds: These are of four types

a) Axillary- Present in the axil of leaf

b) Accesory – Additional buds occuring either on the side or above the axillary bud.

c) Extra axillary- Developing on the node but outside the leaf base.

d) Advventitious – Formed from places other than nodes. These again can be of the following types:

a) Foliar- e,g. Bryophyllum, Begonia

b) Radical- e.g. Dalbergia, Ipomoea Batata ( sweet potato)

c) Cauline – e.g. Jackfruit

Types and Modifications of stem:

(1) Aerial stems ( Epiterranean stem)

It may be reduced, erect and weak.

1) Reduced- Stem reduced to a disc e.g Radish, Carrot, Turnip

2) Erect Stem- is strong and upright eg Maize, Wheat, Mango. An erect stem with swollen nodes is called culm (e.g. Bamboos).

3) Weak stems: are thin , soft and weak and need support. These can be upright or prostate.

(a) Creepers: The stem creeps on earth and the roots arise at the the nodes e.g. Grasses, Strawberry, Oxalis.

(b) Trailers: The stem creeps on the ground but the roots do not arise at the nodes. They may be:

(i) Prostrate or procumbent and diffuse: e.g. Evolvulus, Tribulus.

(ii) Decumbent : e.g. Tridax

(iii) Diffuse : e.g. Boerhaavia

(c) Lianas (Stem climber): Woody perennial  climbers found in tropical rain forests are lianas.

They twine themselves around tall trees to secure sunlight e.g. Hiptage, Bauhinia vahlii ( Phanera).

(d) Climbers : Plant are with long weak stem and have organs of attachment to climb the object .

They may be:

(i) Rootlet climber: e.g Tecoma, Pothos, Piper betel (paan)

(ii) Hook climber: In Bougainvillea, Duranta

(iii) Tendril climber: Tendrils are thread like structures which help in climbing the plants.

(a) Entire leaf: Leaf (tendril e.g. Lathyrus sativus)

(b) Leaflet: Leaflet tendrillar e.g. Pisum

(e) Twiners: The stem bodily twines around the support without any special  organ of attachment. e.g. Cuscuta, Dolichos, and Quisqualis.

(2) Sub-aerial stem

(i) Runner : It is elongated , prostate, aerial branch with long internodes and roots strike at nodes e.g. Oxalis, Grasses, Hydrocotyl.

(ii) Sucker: It arises by axillary bud of underground part of stem. The branch creeps below the soil surface and grows obliquely upward and producie ng a cluster of leaves above and the cluster of roots below.

(iii) Offset: Short horizontal branch producing a cluster of leaves above and the cluster of roots below e.g. Pistia, Eichhornia.

(iv)Stolon: It is subterranean long lateral branch arising from base of the stem e.g. Colocasia. It first grows obliquely upward and bends down to touch the ground surface.

(3) Underground Stems:

1.Rhizome: It grows parallel or horizontal to soil surface. It bears nodes, internodes, buds and scaly leaves. e.g. Ginger, Banana, Turmeric, Ferns. It is of two types:

(a) Rootstocks: It is upright or oblique with the tip almost reaching the soil surface . e.g. Dryopteris.

(b) Straggling : It is horizontal and branched. Branching may be:

(i)Racemose- Axis is monopodial e.g. Saccharum, Lotus.

  

(ii) Uniparous cymose- Axis is sympodial e.g. Zingiber officinale (ginger), Curcuma domestica   (turmeric) and Canna.

   

(iii)Tuber: It is the terminal portion of of underground stem branches which are swollen on account of accumulation of food  e.g.  Potato, Jerusalem artichoke (Helainthus tuberosus).

(iv) Corm: It grow vertically on the soil surface. It bears nodes internodes , buds and scaly leaves.  e.g Colocasia, Gladiolus, Colchicum, Crocus, Amorphophallus.

(v) Bulb : Stem is reduced and discshaped. Yhe bud is surrounded by many concentric leaves. The leaf baes are fleshy and edible. e.g. Onion, Lily, Garlic.

Bulb may be tunicated or scaly.

(a) Tunicated ( layered or laminate ) Bulb is covered with a dry membranous sheath of scales called tunic. These bulbs again of two types:

(i)  Simple tunicated: Onion , Tulipa and Narcissus.

(ii) Compound tunicated bulb: e.g Garlic

(b) Scaly or imbricate or naked bulb- Tunic is absent e.g. Lily.

4, Special stem modifications

(i)Phylloclade:It is green, flattened, or rounded succulent stem with leaves either feebly developed or modified into spines e.g. Opuntia, Casurina.

(ii) Cladode: Phylloclade with one internode is called cladode. e.g. Asparagus, Ruscus.

(iii) Thorn: It is modification of axillary bud e.g. Bougenvillea, Duranta, Carrisa, Alhagi etc. Thons of Alhagi possess flower  and in Duranta thorns bear small foliage leaves. Thorns of carissa are terminal and branched.

(iv) Stem Tendril: e.g. Vitis, Passiflora.

(v) Bulbils: A condensed axillary bud ( vegetative) is called bulbil. It helps in vegetative reproductin. e.g. Dioscorea,Glabba, Agave, Oxalis.

Branching of stem:

The mode of arrangement of branches on the stem is called branching. The branching is of two types:

1.) Lateral branching: The branches are produced laterally from the main stem. It may be racemose or cymose type.

a) Racemose type: The main stem grows -indefinitely by the terminal bud and produces branches laterally in the acropetal succession.

b) Cymose type: The growth of the main stem is limited and lateral branches produced by the main stem show more vigorous growth .It may be of following types:

(i) Uniparous cyme:- When only one lateral branch is produced at a time. It has two distinct types:

a) Helicoid- e.g  Saraca

b) Scorpoid- e.g. Vine

(ii) Biparous cyme- At one time when two or more branches develop e.g. Mirabilis, Datura.

(iii) Multiparous cyme- When more than two branches develop at a time  e.g. Croton, Euphorbia

2. Dichotomous branching- When the terminal bud gives out two branches of equal size in a forked manner e.g. Pandanus, Hyphaene.

C.Leaf (phylopodium)

Leaves are lateral , flat  green and expanded part of plant which arise from the nodes on the stem or branches. The leaf has a bud in the axil. The photosynthesis  and the transpiration occurs by means of leaves. Allthe leaves of a plant are called phyllome. The leaves are of the following typres:

1) Cotyledonary leaves; Are embryonic or seed leaves.

2)Cataphylls: Are scale leaves. These may store food also. eg. Onion.

3) Hyposophylls or bract leaves

4) Prophylls- The first formed leaves

5) Floral leaves- Include sepals, petals and perianth

6) Sporophylls- Bear spores, also used for stamens and carpels.

     

7)Foliage leaves: Green leaves of the plant are called foliage leaves.

   

Parts of a Leaf:

A leaf consisits of the following three parts:

Leaf Base ( Hypopodium): Laeves are attached to stem by leaf base. In some plants , leaf base becomes swollen and is known as pulvinus which is responsible for sleep movement e.g. Cassia, Mimosa, Bean. In some plants leaf base expands into sheath ( sheathing leaf base) e.g. Grasses, Banana ( mnocots).

When the leaf base partially encloses appendages arising from the leaf base is known as Stipules.

Leaves with stipules are called Stipulate ( e.g. Rosa, Polygonum) and those without stipule are called exstipulate e.g. Ipomoea

Parts of Leaf

Types of Stipules: Depending on the stipules are of the following types:

a) Caducous: They fall off before unfolding of leaf e.g. Michelia champaca.

b) Deciduous: Fall off soon after unfolding of leaves. e.g. Cassia tora, Dilenia indica.

c) Persistent: They remain attached to the leaf throughout life. e.g. Rose, pea

On the basis of structure and relation to the leaf stipules are classified as :

1) Free Lateral: These are free, present , on the two sides of the leaf base. e.g. Hibiscus rosa – sinensis.

2) Scaly: Small dry scales present on the two sides of the leaf base e.g. Desmodium.

3) Intrapetiolar: They are situated between the petiole and axis e.g. Gardenia.

4) Foliaceous: Large green leafy structures , two in number e.g. Pea ( Pisum) and Sweet pea ( Lathyrus)

5). Tendrillar: One tendrillar stipule lies on each side of the petiole e.g. Smilax.

(ii) Petiole ( Mesopodium): Petiole in Eichhornia becomes spongy and bulbous. In Orange ( Citrus palnts) petiole becomes winged. Petiole is modified into tendrils in Clematis. In Australian Acacia , petiole is modified into leaf like sickel shaped phyllode.

(iii) Lamina( Epipodium):The broad flat part of the leaf is the lamina ( i.e the leaf blade)

 

Types of Leaf:

(A) Simple leaf: Leaf which may be entire or incised and the incisions do not touch the midrib e.g. Mango, Banyan.

(B) Compound Leaf: Leaf Blade is incised upto midrib or petiole thus dividing it into two or more leaflets.

They are of two types:

1. Pinnately compound leaves: The rachis bears a number of lateral leaflets. These may be:

(i) Unpinnate

(a) Paripinnate e.g. Cassia, Sesbania

(b) Imparipinnate e.g. Rosa, Tephrosia, Azadirachta

(ii) Bipinnate e.g. Acacia, Mimosa, Delonix

(iii) Tripinnate: e.g. Moringa, Melia, Azadirachta

(iv) Decompound: e.g. Daucus carota ( carrot) Parthenium, Coriandrum

2. Palmately compound leaves: It has no rachis and all the leaflets are joined to a common point at the tip of petiole. They may be:

(i) Unifoliate- e.g. Citrus

(ii) Bifoliate- e.g. Bignonia grandiflora, Princepia, Balanites, Hardwickia.

(iii) Trifoliate or ternate: e.g. Medicago, Aegle, Oxalis, Dolichos.

(iv)Quadrifoliate- e.g. Marsilea, Paris quadrifolia

(v) Multifoliate: Cleome, Bombax

Venation in Leaves:

Arrangement of veins on the lamina is called venation . It is of three types:

1. Reticulate venation:  The branches of veins form a network, e.g. Dicots. There are some dicots which show parallel venation. e.g. Calophyllum, Eryngium, Corymbium.

It can be of two types:

(i) Pinnate or unicostate- e.g. Mango, Banyan, China rose.

(ii) Palmate or multisostate

(a) Convergent e.g. Zizyphus, Smilax

(b) Divergent e.g. Castor (Ricinus) Luffa, Vitis ( Grape vine)

2. Parallel venation: The veins and veinlets remain parallel to each other e.g. Monocots. Some monocots which show reticulate venation are e.g. Similax, Dioscorea, Alocasia.

This is of two types:

(a) Pinnate or unicostate parallel venation: e.g. Banana ( Musa paradisiaca), Canna

(b) Pamate or multicostate: (i) convergent e.g. Bamboo, Grass or (ii) divergent e.g. Fan palm.

3. Furcate: The veins branch dichotomously but in the finer branches do not form reticulum. It is very common in ferns. ( e.g. Adiantum) Among the higher plants it is seen in Circeaster

Phyllotaxy:

It is the mode of arrangement of leaves on the stem or its branches. It is of the following types:

1. Alternate: Single leaf arising at each node e.g. Mustard

2. Opposie: Leaves occuring inpairs at the node They may be:

(a) Decussate: Leaves that stand at right angle to next upper or lower pair. e.g. Calotropis (ak) Ocium sanctum ( Sacred basil), Zinnia

(b) Superimposed: Leaves that stand parallel to next upper or lower pair. e.g. Psidium ( Guava), Eugenia jambolana (jamun).

3. Whorled: leaves occuring in more than two at each node. e.g. Nerium, Alstonia.

Heterophilly

The occurence of more than one type of leaves on the same plant is known as heterophylly. It is of three types:

1. Developmental Heterophylly: Leaves of different forms and shape occur at different periods or places on the same plant . e.g. Mustard, Sonchus, Eucalyptus.

2. Habitual Heterophylly: Leaves differ in their shapes and incisions due to their habit or nature . e.g. Artocarpus, Heterophyllus ( Jack fruit) Ficus heterphylla.

3. Environmental Heterophylly: Found in the aquatic plants where the submerged leaves  differ from the floating and aerial leaves e.g. Sagittaria , Ranunculus aqutilis , Limnophilia heterophylla.

D. Inflorescence:

The arrangement of flowers and mode of  distribution of flowers on the shoot system of a plant is called inflorescence.

(A) Racemose ( Indefinite)

Main axis of inflorescence does not end in a flower but continues to grow. The development of flowers is acropetal. The opening   of flowers is centripetal. It is of the following types:

(i) Raceme: Peduncle has bisexual  and pedicellate flowers arranged acropetally  e.g. Larkspur, Mustard, Radish.

(ii) Spike: Peduncle has bisexual and sessile flowers. e.g. Acyrantes, Adhathoda

(iii) Corymb: The main axis is short. Lower flowers have long pedicels than upper ones so that all the flowers fall on the same level.

 Compound corymb: e.g. Cauliflower.

(v) Umbel : The main axis reduced very much and all flowers appear to be arising from the same point. At the base of flowers , clusters of bracts form involcre. e.g. Hydrocotyle, Onion.  Compound umbel e.g. Coriander , Carrot , Prunus

Spadix: It is  a spike with fleshy axis and having both male  and female flowers . It is surrounded by a large coloured bract called spathe. e.g. Musa, Palm, Colocasia, Alocasia ( Characteristic of monocots).

(vi) Catkin: It is a pendulous spike which bears unisexual flowers . e.g. Morus, Birch, Cak, Acalypta.

(vii) Capitulum or head: Main axis becomes flat and is known as receptacle which bears many sessile and small florets. Peripheral florets called ray florets are pistillate or neuter and zygomorphic whereas disc florets are bisexual and actinomorphic. e.g. Sunflower, Zinnia, Cosmos ( Asteraceae)

(viii) Panicle: Peduncle is branched and the branches have pedicellate flowers e.g. Gulmohar, Rhus.

(ix) Spikelet: It is a small spike Flowers are produced in the axil of fertile glumes ( bract) e.g. Wheat, grasses, ( Poaceae).

B) Cymose ( Definite):

main axis ends in a flower. The development of flowers is basipetal and and opening of flowers is centrifugal.

It is of the following types:

(i) Monochasial or uniparous cyme: It is of two types:

(a) Helicoid cyme: e.g. Atropa, Datura, Begonia, Heliotropium

(b)Scorpoid cyme: e.g. Solanum nigrum, Ranunculus

(ii) Dichasial or biparous cyme: Dianthus, Clerodendron.

(iii) Polychasial or multiparous cyme: e.g. Hamelia, Calotropis

C)Special Inflorescence:

These are of following types:

(i) Verticillaster: A cluster of sessile or sub sessile flowers borne on a dichasial cyme ending in monochasial chyme  ( scorpioid) in the form of condensed whorl on either side of the node.  e.g. Ocimum ( Tulsi), salvia ( Lamiaceae).

(ii) Cyanthium: It looks like a single flower. The cup shaped involucre encloses a single female flower and a number of male flowers. Each male flower is represented by single stamen e.g. Poinsettia ( Euphorbia pulcherrima).

(iii) Hypanthodium: Fleshy receptacle forming a hollow cavity with an apical opening. The flowers are eveloped on inner wall of the hollow cavity. The male flowers are situated at the top near the opening, below them the gall flowers whcih are sterile and are at the bottom are situated female flowers with a long style. e.g. Ficus ( Banyan Fig, Gular)

(iv) Coenanthium: In Dorstenia the receptacle becomes saucer shaped and its margins are slightly curved. The florets are arranged assimilar to hypanthodium.

E.Flower:

(A) A flower is defined as a highly condensed and modified reproductive shoot. The following are the points whcih justify that a flower is a modified shoot.

(i) Calyx, Corolla, Androecium and Gynoecium represent four whorls of sterile and fertile leaves borne at different nodes. The internodes between calyx and corolla become elongated and is termed as anthophore. e.g. Silene, Dianthus. The internode corolla and androecium is known as androphore e.g. Passiflora. The internode between androecium and gynoecium is termed as gynophore e.g. Capparis. When androphore and gynophore both are present in the same flower they are jointly termed as gynandrophore e.g. Gynandropsis, Cleome. The prolongation of thalamus beyond carpel is known as carpophore e.g. Coriandrum, Foeniculum.

(ii) In Mussaenda , sepals enlarge to form leafy structure ( foliaceous sepals)

( iii) The floral bud at times get transformed into vegetative bud or bulbils e.g. Agave.

(B)  Technology

(i) Complete Flower: Calyx, corolla, androecium, gynoecium are present

(ii) Incomplete Flower: Flower with one of the four whorls missing.

(iii) Bisexual Floer: Both gynoecium and androecium present in the same  flower.

(iv) Unisexual  flower: Androecium ( Staminate flower) or gynoecium ( pistillate flower) only present in the flower.

    

(v)Monoecious plant: When both male and female flowers are present on  same plants e.g. Cocos, Ricinus, Zea, Colocasia, Acalypha.

      

(vi)Dioecious plant: When the male and female flowers are present on separate plant e.g. Mulberry, Papaya .

     

(vii)Polygamous plant: When unisexual ( male or female) bisexual or neuter flowers are present on the same plant . e.g. Polygonum , mango.

       

(viii)Monocarpic plant: The plant which produces flower and fruit only once in a life time is called     as monocarpic plant. e.g. Pea, Mustard, all seasonal plants.

   

(ix)Polycarpic plant: The plant which produces flowers and fruits many times in life . e.g. Mango,       Pear, ( mostly fruit trees).

(x) Achlamydeous flower: Flowers are naked without sepals and petals. e.g. Piperaceae.

(xi) Monochlamydous flower: Only one whorl is present ( perianth ) e.g. Polygomaceae, Liliaceae.

(xii) Dichlamydeous flower: Both whorls present in a flower e.g. Most of the flowers.

(xiii) Hemicyclic or spirocyclic flowers: Some of the floral parts are in circles and some are spirally arranged. e.g. Ranunculaceae.

(xiv) Cauliflory: Production of flowers on old stem from dormant buds e.g. Artocarpus, Ficus.

(C) Symmetry of Flower:

(i)Actinomorphic flower : When a flower can be divided into two equal halves by many  vertical sections passing through the centre e.g. Cruciferae, Malvaceae.

(ii) Zygomorphic flower: When a flower can be divided into two equal halves by only one vertical section passing through the centre. e.g.,Pea.

(D) Position of Floral parts on thalamus:

(i) Hypogyny: Ovary is at the top and separable from thalamus. Flowers are hypogynous and ovary is superior. e.g. Malva, Brassica.

(ii) Perigyny: Ovary is half superior, half inferior. e.g. Rose.

(iii) Epigyny: Calyx and Corolla arise from upper side of ovary. Ovary is completely surrounded by and fused with thalamus. Ovary is inferior and flower is epigynous e.g. Aster, Luffa.

(E) Bracts:

Bracts are specialized leaves arise from the axil of leaves. They are of following types:

(i) Petaloid bracts: Bracts look like petals ( brughtly coloured) e.g. Bougenvillea.

(ii) Spathy bract: This is a large bract enclosing  an inflorescence e.g. Banana, Maize, Palms.

(iii) Foliaceous bracts: Bracts are leaf like in apearance e.g. Adhatoda, Gynandropsis

(iv) Involucre: They are green – coloured and in one or more whorls a round or below the entire inflorescence e.g. Sunflowere, Coriander.

(v) Glumes; These are small dry scaly bracts found in spikelet of Gramineae. e.g. Wheat.

(F) Calyx:

Lower most whorl of a flower , is known as calyx. It is non essential whorl and consisits of sepals . They may be free ( polysepalous) or fused ( gamosepalous). The sepals are modified as follows:

(i) Pappus: Sepals are modifie into persistent hairy structure called pappus which help in the dispersal of fruits. e.g. Sunflower, Sonchus ( Asteraceae)

(ii) Leafy : In Mussaenda one sepal modified into large leaf like whorl structure.

(iii) Spinous: In Trapa, the calyx is persistant and modified into two spines.

(G) Corolla

It is second whorl of flower and consists of a number of petals which are usually brightly coloured. The petals may be gamopetalous (fused) or polypetalous (free) . The variuos forms of petals are:

(i) Cruciform: Four petals arranged like a cross e.g. Members of Brassicaceae.

(ii) Pappiloneceous: Number of  petals is five with largest petal standard or vexillum enclosing two lateral wings which are free in turn encloses the innermost keel ( united petals ) e.g. Pea.

(iii) Rosaceous : Five or many small clawed petals and spread regularly outward. e.g. Rose.

(iv) Caryophyllaceous: Five free long clawed with limbs spread at right angles to claws. e.g. Dianthus.

(v) Tubular: Petals are like a tube e.g. Disc florets of sunflower.

(vi) Infundibuliform: or funnel shaped: Petals are like funnel e.g. Datura.

(vii) Bilabiate ( two lipped) Upper and lower lips are formed by fusion of petals e.g. Salvia , Ocimum.

(viii) Ligulate or strap shaped: Gamopetalous petals forming tongue like structure e.g. Ray florest of sunflower.

(ix) Comanulate or bell shaped: Petals like bell e.g. Physalis.

(x) Rotate or wheel shaped; e.g. Brinjal

(H)Aestivation:

Arrangement of Floral parts in a floral bud is known as aestivation. It may be of following types:

(i) Valvate: When sepals or petals lie very close to each other, without, without overlapping e.g. Mustard.

(ii) Twisted or contorted: When one margin of the sepal or petal overlaps the margin of next and other margin is overlaped by the third one e.g. China rose.

(iii) Imbricate: When both margins of one of the petals are covered by others and both margins of another one are external and of the remaining partly internal, partly external e.g. Cassia, Caesalpinia.

(iv) Quincuntial: When two petals are inner, two petals are outer and one petal is partly outer and partly inner e.g. Ranunculus.

(v) Vexillary: The posterior petal is the largest and almost covers the two lateral petals and the latter in turn nearly overlap the two anterior petals e.g. Pea (Papilionaceae).

Different types of aestivation A: Quincunical B:  cochlear  aufsteigend C: cochlear absteigend    D:  Contorted E: Valvate  F: open

(I) Androecium

It is the third and male whorl of flower in which each stamen consists of filament, anther and connective.When the stamens  are free it is called polyandrous eg. Lily, Mustard, Radish. Two lobed anther is called bithecous ( e.g. Pea) and one lobed anther which is called as monothecous ( e.g. Members of Malvaceae).

Attachment of the filament to the anther:

(i) Adnate: The filament runs along the back to the anther e.g. Michelia ( Champa)

(ii) Basifixed: Anther is fixed to the filament by its base e.g. Datura.

(iii) Dorsifixed: Anther is fixed to the filament by its back and anther is immobile. e.g. Passion flower.

(iv) Versatile: Anther is attached to the filament as in dorsifixed but is able to swing freely e.g. Wheat and Grasses.

Cohesion of Stamens

Fusion of stamens among themselves is called cohesion. It is of following steps:

(i)Monadelphous: Stamens may  be united by means of their filaments in one bundle e.g. China rose, Lady's finger, Cotton ( Malvaceae).

(ii) Diadelphous: When the filaments are united into two bundles , the anthers remain free e.g. Pea, bean, Gram ( Papillonaceae)

(iii) Polyadelphous: When the filaments are united into more than two bundles but anthers are free e.g. Castor ( Euphorbiaceae) , lemon ( Rutaceae).

(iv) Syngenesious: When anthers are united  but the filaments are free , e.g. Sunflower (  Compositae)

(v) Synandrous: When anthers as well as filaments of stamens are united throughout their whole length . e.g. Members of Cucurbitaceae.

Adhesion of Stamens:

Fusion with other floral parts:

(i) Epipetalous: When stamens are united to the petals e.g. China rose, Solanum, Sunflower.

(ii) Episepalous: When stamens are united to sepals e.g. Verbena.

(iii) Epiphyllous: ( Epipetalous) When the stamens are united to perianth e.g. Members of Liliaceae.

(iv) Gynandrous: When the stamens are attached to gynoecium ( carpel) either throughout their whole length or by their anthers only e.g. Calotropis, ( forming gynostegium)

Length and  Arrangement of stamens:

(i) Didynamous: Four stamens , two outer small and two inner long e.g. Ocimum, salvia ( Labiatae)

(ii) Tetradynamous: Six stamens , two outer small and four inner long e.g. Mustard, Radish ( Brassicaceae) .

(iii) Heterostemony: Stamens are of different lengths e.g. Cassia.

(iv)Obdiplostemonous: Two whorls of stamens , outer lying oposie to the petals ( antipetalous) and inner whorl lying opposite to sepals ( antisepalous) e.g. Stellaria ,  Spergula, and members of Rutaceae.

(v) Diplostemonous: Two whorls of stamens  with the outer whorl lying opposite to sepals ( antisepalous ) and inner whorl lying opposite to petal ( antipetalous) e.g. Cassia.

(J) Gynoecium:

It is the female part of flower comprising of carpels bearing ovules. It consists of ovary , style, and stigma. Thegynoecium may be monocarpellary or polycarpellary.

Cohesion of carpels:

(i) Apocarpous: carpels are free ( no cohesion) e.g. Ranunculaceae

(ii) Symcarpous: carpels more than two and fused e.g. Most of the plants.

Number of locules: Ovary has locules or chambers and may be unilocular, bilocular, trilocular, tetralocular or pentalocular ( multilocular)

Placentation

The arrangement of ovules on placenta within the ovaryy is called lacentation.

It is of the following types:

(i) Marginal: Placenta developing along the junction of the two margins of the carpel in one chambered ovary. It is characteristic feature of family Leguminosae. e.g. Pea, Gram.

(ii) Parietal: Ovary is one chambered and the placentae bearing the ovules develop on the inner wall of the ovary. The number of placenta corresponds to the number of carpels e.g. Mustard, Radish, Cucumber.

(iii) Axile: The ovary is two to many chambered and placenta bearing ovules develop on the inner wall of the ovary. The number of placenta corresponds to the number of carpels e.g. Mustard, Radish, Cucumber.

(iv) Free central: Ovary is one chambered and the placenta bearing the ovules develops all round the central axis. e.g. Dianthus, Stellaria.

(v) Basal: Ovary is unilocular and the placenta  develops at the base of the ovary on the thalamus and bears a single ovule e.g. Wheat, Maize, Aster, Zinnia, Sunflower. It is most advanced.

(vi) Superficial: Ovary is multilocular with numerous carpels as in axile type of placentation but placenta develops all round the iner surface of the partition wall. e.g. Water lily. It is most primitive.

Fruits: Fertilized and ripened ovary is fruit. A fruit consists of (i) Pericarp ( fruit wall) – develops from the wall of ovary and is differentiated into epicarp, mesocarp, and endocarp. (ii)  Seeds- develop from ovules.

In some plants ovary grows into fruit without fertilization , such fruits are called parthenocarpic fruits. They are seedless e.g. Banana, Grapes, Pineapple, Oranges.

The fruit which develops from ovary is called true fruit. Most of the fruits are true fruits. If any other floral part takes part in fruit formation, it is called false fruit. (pseudocarp) e.g. Apple, Pear.

Classification of different kinds of  fruits:

Types of Fruits: These are developed from the ovary of the single flower with or without accessory parts.

(a) Dry indehiscent fruits: They do not split or burst. Seeds liberated only by the destruction of pericarp.          

(b) Dry dehiscent fruits:These fruits burst autamatically and discharge their seeds

(c) Dry Scizocarpic fruits: They are intermediate between dehiscent and indehiscent fruits. One seeded indehiscent parts are called mericarps while dehiscent one seeded are termed cocci.

(d) Flashy or succulent fruits.Pericarp and associated structure becomes fleshy.

2.Aggregate fruits:

These fruits formed from polycarpellary, apocarpous- ovary. Each carpel develops into a fruitlet  and all fruitlets together form an aggregate fruit. An aggregate of simple friuts borne , by a single flower is otherwise known as ' eterio'

3. Multiple or composite fruits:

The fruits develop from entire inflorescence. Sorosis develop from spike , spadix or catkin inflorescence.

G. Seed: Morphologically ripened ovule is known as a seed.Seed is a mature , integumented megasporangium. Seeds are characteristics of Spermatophytes( Gymnosperms and Angiosperms)

Parts of Seed:

1. Seed coat: Outer protective covering of the seed is called seed coat, which develops from the integuments of the ovule. In seeds developing from bitegmic ovules , there are two distinct layers in seed coat.  The outer layer is thick , hard, and leathery  ( developing from outer integument) called testa , wheras th inner layer is thin and papery ( developing from inner integument) called tegmen. In seeds developing from unitegmic ovules there is single layered seed coat.

Embryo:

Embryo is the most important  part of the seed , which represents tiny future plant.  The embryo is having an embryonal axis or the main axis is called tigellum, to which one or two cotyledons are attached depending whether the seed is monocot or dicot. The portion of embryonal axis or tigellum below the point of attachment of cotyledons, is called hypocotyl, which bears radicle  or future root at its tip. The portion of embryonal axis or tigellum above the point of attachment of cotyledons , is called epicotyl, whcih bears plumule ( future shhot) at its tip.

Structure of a seed

Seed structures. (a) Median longitudinal section of pea ovule shortly after fertilization, showing attachment to pod tissues. (b) Mature kidney bean. (c) Mature castor bean. (d) Opened embryo of mature kidney bean.

In some seeds ( e.g. Legumes) reserved food is stored in cotyledons  , whereas in others  ( e.g. Cereals, castor etc wheras seeds in which endosperm is fully consumed by embryo and no endosperm is left , are called , non endospermic or ex-albuminous seeds, e.g gram, pea, sem, cucumber, tamarind, etc. The reserve food materials in seeds may be carbohydrates ( e.g. Wheat, rice)

(i) All the structures inside the seed coat constitute kernel

(ii) In monocot embryo, there is a single cotyledon called scutellum, which is attached to the mid part of the embryonal axis on its lateral side. On the opposite side of the scutellum a tongue shaped flap   like organelle is present called epiblast ( wheat) which represents reduced cotyledon. Furher there is a covering or sheath of radicle alled colerhiza and the sheath of  plumule is called coleoptile.

Structure of maize seed:

(iii) In castor seed( Ricinus communis), there is a specific outgrowth called caruncle or strophiole present over hilum . It is formed by proliferation of cells of outer integument at tip. Caruncle is spongy and helps in absorption of water during germination of seed.

(iv) Perispermic seed: Mostly nucellus, is consumed after fertilization due to absorption of food by th endosperm and the embryo. The remains of the nucellus in the seed is called perisperm. The seeds are called as perispermic seeds. e.g. Piper nigrum ( Black pepper).

(v) Chalazospermic Seeds: Chalazosperm is perisperm like tissue in chalazal region. It is a substitute for endosperm e.g. Cynastrum.

Description of some important families

1.Brassicaceae (Cruciferae)

A.Distinguishing features:

(a) Cruciform corolla

(b) Tetradynamous condition at times didynamous

(c) Presence of 'replum' or false septum in ovary

(d) Parietal placentation

B.Important plants:

(i)Brassica campesteris(Mustard)

(ii) Brassica Oleracea var. Botrytis ( Cauliflower)

(iii) Brassica oleracea var. capitata (Cabbage)

(iv) Iberis amara (Candytuft)

Floral diagram of Brassicaceae

Floral formula

2. Fabaceae(Papillonaceae)

A.Distinguishing features:

(i) Flower Zygomorphic

(ii) Papillionaceous corolla

(iii) Diadelphous androecium

(iv) Marginal placentation

B.Important plants:

(i) Pisum sativum ( Garden pea)

(ii) Cajanus cajan ( Arhar)

(iii) Cicer arientum ( Gram)

(iv) Glycirrhiza glabra ( Mulathi)

(v) Abrus pecatorius ( Ratti)

(vi) Phaseolus radiatus(moong)

Floral diagram of  Fabaceae

3. Asteraceae ( compositae)

A.Distinguishing features:

(i) Epigynous flowers

(ii) Calyx moified into hair like structure pappus

(iii) Ligulate corolla  in ray floret and tubular corolla in disc floret

(iv) Ray florets are zygomorphic and disc florets are actinomorphic.

(v)Syngensious and epipetalous condition

(vi) Inferior ovary

(vii) Basal placentation

B. Important Plants:

(i) Helianthus annus ( Sunflower)

(ii) Tagetes patula (Marigold)

(iii) Carthamus tinctorius (Safflower)

(iv) Parthenium hysterophorus( Congress grass)

disc floret:

formula of ray floret

4.Solanaceae

A.Distinguishing features:

(i) Stamens 5, polyandrous, epipetalous.

(ii) Axile placentation

(iii) Ovary obliquely placed

(iv) Placenta swollen

B. Important plants:

(i) Solanum tuberosum ( potato)

(ii) Solanum melogena ( Brinjal)

(iii) Withania  somnifera ( Ashwagandha)

(iv) Lycopersicon esculentum( Tomato)

(v) Capsicum frutescens ( Shimla mirch)

(vi) Nicotiana tabacum ( Tobacco)

Solanaceae

5. Liliaceae

A.  Distinguishing features:

(i) Trimerous flower.

(ii) Epiphyllous condition.

(iii) Perianth 6 , in two alternate whorls

(iv) Axile placentation

(v) Unisexual flowers in Ruscus and Smilax

B:Important  plants:

(i) Allium cepa (Piaz)

(ii) Allium sativum ( Garlic)

(iii) Yucca

(iv) Smilax

(v) Ruscus

(vi) Lilium

Floral formula: Liliaceae

6.Poaceae ( Graminae)

(i) Inflorescence

(a) spike of spikelet (Triticum)

(b) Panicle of spikelet (Avena)

(ii) Lemma bear a long , stiff process called awn.

(iii) Perianth represented by two lodicules

(iv) Versatle fixation of anthers

(v) Basal placentation

(vi) Feathery stigma

Important plants:

(i) Avena sativa ( Oat)

(ii) Triticum aestivum  ( Wheat)

(iii) Zea Mays ( Maize)

(iv) Oryza sativa (Rice)

(v) Saccharum officinarum ( sugarcane)

(vi) Sorghum vulgare ( Jawar)

  

Poaceae ( Graminae)

Economic Importance of Papillinoceae:

(i) Source of pulses.

(ii) Edible oil

(iii) Dye

(iv) Fodder ( Sesbania)

(v) Ornamentals ( lupin, sweet pea)

(vi) Medicine ( mulaithi)