Morphology of Flowering Plants Part 1
• Rotate : Short tubular corolla with spread out lobes appearing like a wheel e.g., Brinjal.
• Hypocrateriform : It is a salver shaped corolla. It is provided with a elongated narrow tube having lobes
at the top placed at right angles, e.g., Vinca.
• Ligulate : Corolla with a short tube which is drawn out into a tongue shaped structure e.g., ray florets of
Asteraceae.
• Bilabiate : The irregular corolla is united, in such a way that it appears two lipped. It is the characteristic
corolla of labiatae, e.g., Leucas.
(vi) Aestivation : The arrangement of sepals and petals in bud condition of the flower is called “aestivation”.
It is may be of following types :
(a) Open : If the margins of perianth members in a whorl are free with wide gap between them, then the type
of aestivation is called ‘open’, e.g., sepals of Mustard.
(b) Valvate : Here the edges of perianth members in a whorl are very nearly touching each other bud do not
overlap, e.g., calyx and corolla in Annona.
(c) Twisted : In this type, the perianth members of a whorl show one edge outside and one edge inside. Thus
they regularly overlap the neighbouring members on one side. The twisted aestivation is also called contorted or
convolute aestivation, e.g., corolla of Hibiscus.
(d) Imbricate : Here in a whorl of perianth members, one is completely inside and another is completely
outside. The remaining perianth members show one edge inside and the other edge outside. The imbricate
aestivation is of two types, namely, descending imbricate and ascending imbricate.
• Descending imbricate : Here the odd
petal is posterior and completely outside. The anterior
pair of petals are completely inside. The remaining
petals show regular overlapping in the descending
manner. It is also called vexillary aestivation, e.g.,
Tephrosia, Crotalaria and Dolichos.
• Ascending imbricate : Here the odd (A) (B) (C) (D) (E)
petal is posterior and completely inside. One of the
anterior petals is completely outside. The remaining Fig : Different types of aestivation
petals show regular overlapping in ascending manner, (A) Valvate, (B) Twisted, (C) Imbricate, (D) Quincuncial
e.g., Cassia and Delonix.
(E) Vexillary
(e) Quincuncial : In this type, out of the five perianth members in a whorl two are completely outside, two
are completely inside and the remaining has one edge outside and one-edge inside. This is confined to
pentamerous flowers only, e.g., sepals of Ipomoea, Vinca and Thevetia.
(vii) Androecium : It is the third whorl of a flower consisting of stamens or microsporophylls. Fertile stamens
produce pollen grains. Staminodes are the sterile stamens. Petaloid stamens are brightly coloured and appear like
petals, e.g., Canna.
Chapter 14 205
Morphology of Flowering Plants Part 1
(a) Structure of stamen : A stamen shows a long or short stalk called the filament. The filament ends with a
terminal fertile part known as the anther. It encloses microsporangia within which microspores or pollen grains are
produced. The filament of the stamen is connected to the anther by means of a “connective”. The anther may be
monothecous or dithecous. The monothecous anther has only one sac. It is bilocular or bisporangiate, e.g.,
Hibiscus. The dithecous anther consists of two sacs and is tetralocular or tetrasporangiate in as Datura.
When the face of anther is towards centre of flower it is called introrse e.g., tomato when it is towards the
periphery it is called extrorse e.g., Ranunculus.
(b) Fixation : The mode of attachment of a filament to Anther
anther by connective is called fixation. It is of following types :
• Adnate : Filament attached to the total length of the Connective
anther on the back. e.g., Michelia (Campa).
Filament
• Basifixed : Filament is attached to the base of the
anther e.g., Datura, Mustard, Radish. (A) (B) (C) (D)
Fig : Attachment of anther to filament
• Dorsifixed : Filament is attached to the anther on the (A) Adnate, (B) Basifixed, (C) Dorsifixed,
dorsal side at middle portion e.g., Passiflora.
(D) Versatile
• Versatile : Filament is attached to the anther at a point so that anther can swing freely in all direction.
e.g., Grasses.
(c) Length of stamens : Based on the relative lengths of the stamens, the conditions of androecium varies :
• Didynamous : When there are four stamens in a flower of which two are long and two are short, the
condition is described as didynamous, e.g., Ocimum.
• Tetradynamous : Out of the six stamens that are found in a flower, four stamens are long and the two
are short. This condition is called tetradynamous, e.g., Raphanus and Brassica.
The stamens are described as inserted when they do not extend beyond the petals or corolla tube (Dolichos).
When the stamens extend beyond the petals or corolla tube, the stamens are known as (Acacia).
(d) Insertion of stamens : Based on the insertion of stamens, the condition of androecium varies :
• Isostemonous : When the stamen form a single whole and the number of stamen is the same as that of
sepals and petals, the flower is isostemonous.
• Diplostemonous : Sometimes there are two whorls of stamens. The first whorl alternating with petals
(antisepalous) and the second whorl alternating with sepals (antipetalous).
• Obdiplostemonous : In this condition first whorl is antipetalous and the second whorl is antisepalous.
(e) Union of stamens : The union of stamens takes place either among themselves (cohesion) or with other
whorls (adhesion).
Cohesion of stamen : Usually three types of cohesion among stamens occur. They are :
• Adelphy : When the filaments of stamens are united and the anthers remain free. It is of three types :
Chapter 14 206
Morphology of Flowering Plants Part 1
• Monadelphous : All filaments unite to form a single bundle e.g., Family malvaceae (Hibiscus).
• Diadelphous : Filaments unite to form two bundles. e.g., family papilionaceae (Pisum, Sesbania, Tephrosia).
• Polyadelphous : Filaments unite to form many bundles. e.g., family rutaceae (Citrus, Melaleuca).
• Syngenesious : When the anther of filament are united and the filaments remain free. e.g., Tridax,
Sunflower etc.
• Synandrous : Here all stamens of a flower are united completely to form a single structure. e.g., family
Cucurbitaceae.
Adhesion of stamens : Stamens may unite with other floral organs like sepals, petals or gynoecium. Based
on the floral organ involved in the union with stamens, the adhesion may be of the following types :
• Epiphyllous : Stamens unite with perianth. e.g., Asperagus.
• Episepalous : Stamens unite with sepals.
• Epipetalous : Stamens unite with petals. e.g., Datura.
• Gynandrous : Stamens unite with gynoecium. It is also called gynandrium or gynostegium. e.g., Calotropis.
(viii) Gynoecium : The gynoecium or pistil is the fourth essential whorl of female reproductive part of the
flower and may be made up of one or more carpels (megasporophylls). A carpel has three distinct part, namely
ovary, style and stigma. The lower most swollen fertile part of the carpel is the ovary. It encloses ovules. Above the
ovary elongated thread like structure attached to the apex of the ovary, the style. The style end with a round, sticky
stigma. A sterile pistil is known pistillode. The number of carpels is a gynoecium vary in different flowers.
Accordingly the gynoecium may be described as follows :
(a) Monocarpellary : It is a ovary with a single carpel, e.g., Bean.
(b) Bicarpellary : It is presence of two carpels in a ovary, e.g., Helianthus.
(c) Tricarpellary : It is presence of three carpels, e.g., Cocos.
(d) Tetracarpellary : It is presence of four carpels, e.g., Cotton.
(e) Pentacarpellary : It is presence of five carpels, e.g., Hibiscus.
(f) Multicarpellary : It is presence of many carpels, e.g., Annona.
When the number of carpels in a gynoecium are two or more, they may be free or united. If they are free it is
called apocarpous gynoecium and if they are fused it is called
syncarpous gynoecium.
The ovary encloses one to many chambers called the locules. Usually Style Style
the number of locules in a syncarpous ovary corresponds to the number of Ovary
carpels. Sometimes, the number of locules may be doubled. e.g., in Datura, Ovary
the gynoecium is bicarpellary syncarpous with four locules in the ovary. lobes
Based on the number of locules, the ovary may be described as follows :
• Unilocular : Ovary with one locule. e.g., Dolichos.
Chapter 14 207 (A) (B) (C)
Fig : Types of styles
(A) Terminal, (B) Lateral,
(C) Gynobasic style
Morphology of Flowering Plants Part 1
• Bilocular : Ovary with two locules. e.g., Solanum.
• Trilocular : Ovary with three locules. e.g., Allium.
• Tetralocular : Ovary with four locules. e.g., Datura.
• Pentalocular : Ovary with five locules. e.g., Hibiscus.
• Multilocular : Ovary with many locules. e.g., Abutilon.
(ix) Placentation : (See the detail in ‘Embryology’ Module : 2)
(x) Style : The stalk like structure present above the ovary is called the style. The style may be long (Datura)
or short (grasses) or absent (Papaver). In the family umbelliferae (apiaceae) the base of the style is swollen and
forms a structure called stylopodium. There are three types of styles as described below :
(a) Terminal style : If the style arises from terminal part of the ovary, it is called terminal style, e.g., Datura,
Hibiscus and Solanum.
(b) Lateral style : If the style arises from one side of the ovary, it is called lateral style, e.g., mango.
(c) Gynobasic style : If the style arises from the base of the ovary it is called gynobasic style, e.g., Ocimum,
Salvia.
(xi) Stigma : The terminal receptive portion of the style is called the stigma. It receptive pollen grain during
pollination. Usually the lobes of the stigma corresponds to the number of carpels. Accordingly the stigma may be
unifid, bifid, trifid, tetrafid, pentafid or multifid.
• Capitate : Round stigma. e.g., Hibiscus.
• Forked : Divided stigma. e.g., Tridex.
• Feathery : Brush like stigma. e.g., Grasses.
(xii) Floral formula : It is an expression summarizing the informations given in a floral diagram. It represents
the informations given in a floral diagram in the form of an equation. Following symbols are used in constructing a
floral formula.
Br. Bracteate C Corolla-free (polypetalous)
Brl. Bracteolate (C) Corolla-united (gamopetalous)
Ebr. Ebracteate Cx Corolla-cruciform
Bbrl. Ebracteolate P Perianth
Male A Androecium-free
♂
Female (A) Androecium-united
♀
Bisexual PA Epiphyllous
♂+ Actinomorphic CA Epipetalous
⊕ Zygomorphic G Gynoecium-free
† or %
Epicalyx (G) Gynoecium-united
Ep Calyx-free (polysepalous) G Superior ovary
K
(K) Calyx-united (gamosepalous) G Inferior ovary
Chapter 14 208
Morphology of Flowering Plants Part 1
G A Gynostagium
(xiii) Floral diagram : Diagram illustrating the relative position and number of parts in each of the sets of
organs comprising a flower. Floral diagram is usually drawn with reference to mother axis. Following signs are used
in constructing a floral diagram.
Mother axis Sepal Petal Petal with nectar
gland
• OR X
Staminode Dithecous Monothecous Monocarpellary Bicarpellary
stamen gynoecium
stamen gynoecium
Multicarpellary Disc secreting Monadelphous Syngenesious
gynoecium nectar androecium androecium
Fig : Signs used in preparation of floral diagram
Chapter 14 209
Morphology of Flowering Plants Part 2
Liliaceae.
Systematic position
Division : Angiospermae
Class : Monocotyledonae
Series : Coronarieae
Order : Liliales
Family : Liliaceae
Habit : Usually perennial herbs growing by means of rhizomes (e.g., Aloe, Polygonatum), bulbs (e.g., Lilium,
Allium) and corms (e.g., Colchicum). Some herbs are annual (e.g., Asphodelus). Shrubs occur in Aloe, Agave,
Yucca (Dagger plants, Adam’s Needle), Dracaena (Dragon plant), and Ruscus (Butcher’s Broom). They mostly grow
in arid areas and are hence xerophytic (e.g., Aloe, Yucca). Xanthorrhoea of Australia is tree-like. Climbers are seen
in Smilax, Gloriosa and species of Asparagus.
Root : Adventitious, fibrous or tuberous (e.g., Asparagus).
Stem : Erect or climbing as Smilex, branched or unbranched, herbaceous, phylloclade as Ruscus. Cladode as
Asparagus, Bulb as Allium cepa.
Leaves : Radical or cauline and ramal, cauline and ramal show various types of phyllotaxy (alternate,
opposite or whorled), exstipulate, stipulate in Smilax where the stipules are prolonged into tendrils, sessile or
petiolate with sheathing leaf bases, venation parallel but reticulate in Smilax, leaves may be scaly, leathery, fleshy or
modified into spines (e.g., Asparagus), leaf apex is tendrillar in Gloriosa. The leaves of Phormium tenax (New
Zealand Hemp) are 3 metres long and 10 cm broad.
Inflorescence : Recemose, sometimes solitary (e.g., Tulipa, Gloriosa) or umbellate condensed cymes (umbel
cyme), e.g., Onion. In several cases the inflorescence possesses a leafless peduncle called scape.
Flower : Bracteate or ebracteate, pedicellate, regular, actinomorphic, zygomorphic in a few cases (e.g.,
Gilliesia), complete or incomplete, perfect, unisexual in Smilax and Ruscus, hypogynous, generally pentacyclic,
trimerous (rarely bimerous or tetramerous). Accessory floral organs undifferentiated and collectively called perianth.
Parianth : Tepals 6, in two whorls of 3 each, free or fused, sepaloid or petaloid, scarious or membranous,
aestivation valvate or imbricate, distinguished into calyx and corolla in Trillium, inferior.
Androecium : Stamens 6 (3 in Ruscus, 9–12 in Tofieldia), free (polyandrous) or monadelphous (e.g., Ruscus),
arranged in two whorls, antiphyllous (antitepalous), may be epiphyllous (or Mother axis
epitepalous), anthers fixed variously (basifixed, dorsifixed, versatile), dehiscence
longitudinal or by pores, inferior.
Gynoecium : Tricarpellary, syncarpous, ovary superior, trilocular with 2-
many ovules in each locules, placentation axile, rarely parietal, styles united or
separate, stigma free or fused, trilobed.
Fruit : A capsule (e.g., Asphodelus, Gloriosa) or berry (e.g., Asparagus).
Seed : Endospermic and monocotyledonous. Fig : Floral diagram of liliaceae
Floral formula : ⊕ +♂ P3+3 or (3+3) A3+3 G(3) (Allium cepa)
Chapter 15 210
Morphology of Flowering Plants Part 2
Cruciferae (Brassicaceae).
Systematic position : Angiospermae
Division
Class : Dicotyledonae
Subclass : Polypetalae
Series : Thalamiflorae
Order : Parietales
Family : Cruciferae (Brassicaceae)
Habit : Annual, biennial or perennial herbs. Farsetia jacquemontii is an undershrub. The plants possess
pungent juice having sulphur-containing glucosides.
Root : Tap root alongwith hypocotyl is swollen in Radish (Raphanus sativus) and Turnip (Brassica rapa).
Stem : Erect, cylindrical, hairy or glabrous, herbaceous or rarely woody. It is reduced in the vegetative phase
in Radish and Turnip. The stem is swollen in Kohlarabi (Knol-Kohl = Ganthgobi, Brassica, oleracea var.
Gonglylodes). Axillary buds enlarged in Brussel’s Sprouts ( = Button gobhi) or Brassica oleracea var. gemmifera.
Brassica oleracea var. capitata (Cabbage) has the largest terminal bud.
Leaves : Radical, cauline and ramal, alternate or sub-opposite but forming rosettes when radical, exstipulate
with sheathing leaf base, sessile simple or rarely compound (e.g., Nasturium officinale), hairy. Bulbils occur in the
leaf axils of Dentaria bulbifera and on the leaves of Cardamine pratensis.
Inflorescence : Flowers are usually arranged in racemose racemes. Occasionally they are in corymbs (candtuft).
Flower : Ebracteate or rarely bracteate (e.g., Rorippa montana), pedicellate, complete, perfect, regular,
actinomorphic, rarely zygomorphic (e.g., Iberis, Teesdalia), tetramerous or bimerous, hypogynous (perigynous in
Lepidium), cyclic, cruciform.
Calyx : Sepals 4, polysepalous, aestivation imbricate, generally arranged in two whorls, outer of antero-
posterior sepals and inner of lateral sepals, lateral sepals generally saccate or pouched at the base, green or
petaloid, inferior.
Corolla : Petals 4, polypetalous, arranged in one whorl and alternate with sepals, often with long claws and
spread out in the form of a Greek cross. This arrangement of petals which is characteristic of the family is known as
the cruciform arrangement and corolla is described as cruciform corolla, valvate aestivation. Petals reduced or
absent in Lepidium and Rorippa.
Androecium : Stamens 6, (four in Cardamine hirsuta, two in Coronopus didymus, 16 in Megacarpaea), free
(polyandrous), tetradynamous, arranged in two whorls, outer of two short lateral
stamens while the inner whorl is made up of 4 long stamens arranged in two Mother axis
median pairs, anthers basifixed or dorsifixed, dehiscence longitudinal, inferior.
Green nectaries are often associated with the bases of stamens.
Gynoecium : Bicarpellary (tricarpellary in species of Lepidium, tetracarpellary
in Tetrapoma and Tropidocarpum), syncarpous, carpels placed transversely, ovary
superior, placentation parietal, ovary bilocular due to the presence of a false septum
called replum, style short, stigma capitate, simple or lobed.
Fruit : Siliqua of silicula, lomentaceous siliqua occurs in radish. Fig : Floral diagram of cruciferae
Seed : Non-endospermic, often oily. (Brassica campesteris)
Chapter 15 211
Morphology of Flowering Plants Part 2
Floral formula : Ebr ⊕ +♂ K 2+2 C×4 A2+4 G (2)
Leguminosae.
Systematic position
Division : Angiospermae
Class : Dicotyledonae
Subclass : Polypetalae
Series : Calyciflorae
Order : Rosales
Family : Leguminosae
Habit : Annual or biennial, herb, shrub or tree.
Root : Tap root system.
Stem : Erect or creeping, solid or weak.
Leaf : Alternate or whorled, stipulate, petiolate, simple or usually compound, reticulate venation.
On the basis of inflorescence and flower characters, this family divided in to 3 subfamilies :
Family – Leguminosae
Papilionatae (Fabaceae) Caesalpinoideae Mimosoideae
1. Flowers – very zygomorphic 1. Flowers – more or less zygomorphic 1. Flowers – actinomorphic
2. Corolla – descending imbricate 2. Corolla – ascending imbricate 2. Valvate, petals free or connate
3. Stamens – diadelphous 3. Some staminodes 3. Stamens – usually indefinite
Subfamily - Papilionatae (Fabaceae)
Inflorescence : Racemose or solitory axillary.
Flower : Bracteate or ebracteate rarely bracteolate (e.g., Arachis), pedicellate or sessile, complete, irregular,
zygomorphic, perigynous or occasionally hypogynous, pentamerous.
Calyx : Sepals 5, gamosepalous, usually companulate, lobe unequal, rarely tubular (e.g, Cyamopsis), odd
sepal anterior, may be persistent inferior.
Corolla : Petals 5, polypetalous, papilionaceous, descending imbricate aestivation, one posterior long
standered, two lateral short wings, two anterior petals jointed to each other
forming keel.
Androecium : Stamens 10, usually diadelphous (9+1 in Lathyrus, 5+5 in
Aeschynomene) or monadelphous (9 in Dalbergia, 10 in Arachis and Erythrina
indica), rarely free (e.g., Sophora), nectar gland often present on the inner bases of
filaments, anther lobes bilocular, dorsifixed, introse.
Gynoecium : Monocarpellary, ovary superior, unilocular with marginal
placentation ovary covered by staminal tube, style bent, stigma simple or capitate.
Fig : Floral diagram of
subfamily papilionatae
(Pisum sativum)
212
Morphology of Flowering Plants Part 2
Fruit : Legume or lomentum.
Floral formula : Br % +♂ K5 C1+2+(2) A1+(9) G1
Subfamily – Caesalpinoideae
Inflorescence : Raceme, umbel or a solitary flower.
Flower : Bracteate or ebracteate, pedicellate, hermaphrodite, complete,
zygomorphic, hypogynous.
Calyx : Sepals 5, polysepalous, imbricate aestivation.
Corolla : Petals 5, polypetalous, ascending imbricate aestivation.
Androecium : 10 stamens, or staminodes are found as in Cassia, free
filaments of unequal size, anther lobes bilocular, introrse, versatile.
Gynoecium : Monocarpellary, unilocular, ovary superior, marginal
placentation, stigma capitate.
Fig : Floral diagram of subfamily
Fruit : Legume. caesalpinoidae (Cassia fistula)
Floral formula : % +♂ K5 C5 A1+ 2+ 2+ 2+3 (staminodes ) or 7+3 (staminodes ) G1
Subfamily – Mimosoideae
Inflorescence : Head or capitulum or spike, flowers arranged in acropetal succession.
Flower : Bracteate or ebracteate, sessile, hermaphrodite, complete actinomorphic, hypogynous,
pentamerous.
Calyx : 5 sepals (4 in Mimosa) gamosepalous, connate at the base, valvate aestivation, rarely imbricate (e.g.,
Parkia).
Corolla : 5 petals (4 in Mimosa) gamopetalous or polypetalous, membranous, valvate aestivation.
Androecium : In most of the members, stamens are indefinite and polyandrous. However, there are only 4
stamens in Mimosa pudica and 10 each in Prosopis and Dichrostachys.
Filaments are long, usually connate at the base, sometimes they are coloured
and gland dotted. Anthers are dithecous and introrse.
Gynoecium : Monocarpellary, unilocular, ovary superior, style long,
cylindrical, stigma single and capitate, marginal placentation.
Fruit : Lomentum.
Floral formula : Br or Ebr ⊕ +♂ K(5) C(5) or 5 A∞ G1 Fig : Floral diagram of subfamily
mimosoidae (Mimosa pudica)
213
Morphology of Flowering Plants Part 2
Solanaceae.
Systematic position
Division : Angiospermae
Class : Dicotyledonae
Subclass : Gamopetalae
Series : Bicarpellatae
Order : Polimoniales
Family : Solanaceae
Habit : Mostly herbs (Petunia, Solanum nigrum, Nicotiana, Withania), shrubs, a few trees (Solanum
grandiflorum or potato tree) or climbers (Solanum jasminoides or potato vine, Solanum dulcamara).
Root : Branched tap root.
Stem : Usually the stem is erect, solid, cylindrical and branched. Occasionally, it is spinous (Solanum
xanthocarpum, Datura stramonium, Lycium). In potato (Solanum tuberosum) underground stem is modified in to
tubers.
Leaves : Cauline, ramal, exstipulate petiolate or sessile, alternate, sometimes opposite, simple, entire,
pinnatisect in tomato (Lycopersicum esculentum). Venation unicostate reticulate, variegated in Solanum
jasminoides.
Inflorescence : Axillary or extra axillary cyme. Solitary axillary in Physalis and Pentunia. Sub-sessile
umbellate cyme in Withania somnifera, solitary in Datura.
Flower : Bracteate or ebracteate, pedicillate, complete, actinomorphic, rarely zygomorphic (e.g., Salpiglosis,
schizanthus), bisexual, rarely unisexual (e.g., Withania coagulans) pentamerous, hypogynous.
Calyx : Sepals 5, gamosepalous, tubular or campanulate, persistent, accrecent (enlarging in fruit, e.g.,
Physalis, Withania), Valvate or imbricate, green or coloured, hairy.
Corolla : Petals 5, gamopetalous, tubular or infundibuliform, valvate, twisted in Datura, bilabiate in
Schizanthus, scale or hair like outgrowth may arise from the throat of the corolla tube.
Androecium : Stamens 5, rarely 4 (e.g., Salpiglosis) or 2 (e.g., Schizanthus), free, epipetalous, polyandrous
alternate to petals, filament inserted deep in the corolla tube, anthers dithecous, usually basifixed or dorsifixed,
introrse.
Gynoecium : Bicarpellary, syncarpous, ovary superior, carpels placed
obliquely in diagonal plane, generally bilocular (2-4 locular in tomato, 4-locular in
Datura due to false septa), placentation axile, ovules many in each locules,
placentae swollen, a nectariferous disc or lobes may be present, stigma capitate or
lobed.
214
Fig : Floral formula of
solanaceae (Solanum nigrum)
Morphology of Flowering Plants Part 2
Fruit : A many seeded berry (e.g. Tomato) or capsule (e.g, Datura).
Seed : Endospermic with straight or curved embryo.
Floral formula : Br ⊕ ♂+ K(5) C(5) A(5) G (2)
Morphology of Flowering Plants Part 2
Compositae (Asteraceae).
Systematic position
Division : Angiospermae
Class : Dicotyledonae
Subclass : Gamopetalae
Series : Inferae
Order : Asterales
Family : Compositae (Asteraceae)
(Largest family among the angiosperms)
Habit : Most of the plants are annual herbs (e.g., Chrysanthemum, Lactuca, Calendula, Helianthus, Tagetes).
A few are shrubs (e.g., Artemisia, Pluchea lanceolata) or rarely trees (e.g., Vernonia arborea, Wilkesia, Leucomeris).
Milkamia cordata is a twiner.
Root : Usually there is a tap root, but in Dahlia and Taraxacum officinale fasciculated roots are present.
Stem : Stem is usually herbaceous, erect, branched, solid, fibrous and sometimes with milky latex. In
Jerusalem artichoke (Helianthus tuberosus) the stem is underground and tuberous. In Baccharis, it is winged like a leaf.
Leaves : Leaves are mostly alternate and occasionally opposite (e.g., Helianthus) or whorled (e.g.,
Eupatorium, Zinnia verticillata). They are exstipulate, petiolate, simple, pinnately or palmately lobed or compound
(e.g., Dahlia, Cosmos). Venation is reticulate.
Inflorescence : Inflorescence is capitulum or head with an involucre of bracts at its base. The number of
flowers in each inflorescence varies from 1000 (in large flowers of Helianthus) to 1 (in Echinops). Peduncle flat on
which florets are attached.
Flower : Epigynous, usually pentamerous with reduction in certain whorls, hermaphrodite or unisexual
complete or incomplete, tubular (actinomorphic) or ligulate (zygomorphic), bracteate or ebracteate.
(1) Ray florets : Towards periphery of head, sessile bracteate, pistillate or neutral, zygomorphic, ligulate,
epigynous.
Calyx : Absent or hairy pappus or scaly, persistant.
Corolla : Petals 5, gamopetalous, ligulate, strap shaped.
Androecium : Absent.
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Morphology of Flowering Plants Part 2
Gynoecium : Bicarpellary, syncarpous, ovary inferior, unilocular, one ovule in each locule, basal
placentation, style simple narrow, stigma branched.
(2) Disc florets : In the centre of head, bracteate, bisexual, actinomorphic, tubular, pentamerous, epigynous.
Calyx : Absent or pappus.
Corolla : Petals 5, gamopetalous, tubular.
Androecium : 2 stamens, epipetalous, syngenesious, dithecous, bilobed, introrse, filament free.
Gynoecium : Bicarpellary, syncarpous, ovary inferior, unilocular, single ovule in the locule, basal
placentation, style single, short, stigma bifid.
(3) Neutral florets : Androecium and gynoecium both are
absent. Remaining structures are similar to ray floret and disc
florets.
Fruit : Cypsella.
Seed : Exalbuminous.
Floral formula :
Ray florets : Br.% ♀ K0 or P C(5) A0 G(2) (A) (B)
Disc florets : Br.% or ⊕ +♂ K0 or P C(5) A(3) G(2)
Neutral florets : % or ⊕ K 0 C(5) A0 G0 Fig : Floral diagram of compositae
(Helianthus annuus)
(A) Ray floret, (B) Disc floret
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Introduction.
The higher plants have highly complex bodies made up of different types of cells. All cells are of same origin
but afterwards they gets differentiated into different types of cells. Cells of similar shape and size constitute a group
which perform diverse functions. A group of cells performing a particular function is collectively called as tissue. A
tissue may be defined as, “a group of similar or dissimilar cells having common origin and performing a specific
functions.”
Tissues are mainly divided into three categories :
(1) Meristematic tissues or Meristems
(2) Permanent tissue
(3) Secretory tissue
Meristematic tissues or Meristems.
The word “Meristem” originated from “Meristos” (Greek = continuous division) and the term meristem was
introduced by Nageli (1858). A group of cells which are much active and capable of showing continuous divisions
and redivisions, is called as meristematic tissue. The various characteristic features of the meristems are discussed
below :
• They contain immature and young cells and are capable of repeated divisions.
• Intercellular spaces are not present in meristematic tissue.
• They contain a homogeneous thin wall.
• They contain large nuclei associated with abundant cytoplasm.
• They are metabolically very active but they do not store food material.
• Only proto-plastids are present instead of plastids, chloroplast absent.
• Dense cytoplasm is present which contains several premature mitochondria.
• Vacuoles are absent.
• Meristematic cells are isodiametric in shape.
• Undifferentiated tissue in which all divides continuously G1 → S → G2 → M.
(1) Types of meristems : The meristems may be classified on the basis of their mode of origin, position or function :
(i) According to origin and development : On the basis of origin, meristematic tissues are of three types :
(a) Promeristem or Primordial meristem : The promeristem originates from embryo and, therefore, called
primordial or embryonic meristem. It is present in the regions where an organ or a part of plant body is initiated. A
group of initial cells that lay down the foundation of an organ or a plant part, is called promeristem. This group
consists of a limited amount of cells, which divide repeatedly to give rise primary meristem. It occupies a small area
at the tips of stem and root. The promeristem gives rise to all other meristems including the primary meristem.
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(b) Primary meristem : A primary meristem originates from promeristem and retains its meristematic
activity. It is located in the apices of roots, stems and the leaf primordia. Primary meristem gives rise to the primary
permanent tissue.
(c) Secondary Meristem : They always arise in permanent tissues and have no typical promeristem. Some
living permanent cells may regain the meristematic nature. This process in which permanent tissue regains
meristematic nature is called dedifferentiation. The secondary meristems are so called because they originate from
permanent cells. The phellogen or cork cambium arising from epidermis, cortex or other cells during secondary
growth, is an important example of secondary meristem. The secondary meristems produce secondary tissues in the
plant body and add new cells for effective protection and repair.
(ii) According to position : On the basis of their position in the plant body meristems are classified into
three categories :
(a) Apical meristem : This meristem is located at the growing apices of main and lateral shoots and roots.
These cells are responsible for linear growth of an organ. The initiating cells may be single or in groups. Solitary
initial cells are known as apical cells whereas those occurring in groups are called apical initials. Solitary apical cells
occur in ferns and other Pteridophytes while apical initials are found in other vascular plants. The apical initials may
occur in one or more tiers. Position of apical cells may either be strictly terminal or terminal and subterminal.
(b) Intercalary meristem : These are the portions of apical meristems Apical meristem
which are separated from the apex during the growth of axis and formation of Intercalary meristem
permanent tissues. It is present mostly at the base of node (e.g., Mentha viridis-
Mint), base of internode (e.g., stem of many monocots viz., Wheat, Grasses,
Pteridophyts like Equisetum) or at the base of the leaf (e.g., Pinus). The
intercalary meristems ultimately disappear and give rise to permanent tissues.
(c) Lateral meristem : These meristems occur laterally in the axis, Lateral meristem
parallel to the sides of stems and roots. This meristem consists of initials which
divide mainly in one plane (periclinal) and result increase in the diameter of an aa
organ. The cambium of vascular bundles (Fascicular, interfascicular and AB
extrastelar cambium) and the cork cambium or phellogen belong to this
category and are found in dicotyledons and gymnosperms. Fig : Various meristamatic tissue
(iii) According to function : Haberlandt in 1890 classified the primary
meristem at the apex of stem under the following three types :
(a) Protoderm : It is the outermost layer of the apical meristem which develops into the epidermis or
epidermal tissue system.
(b) Procambium : It occurs inside the protoderm. Some of the cells of young growing region which by their
elongation and differentiation give rise to primary vascular tissue, constitute the procambium.
(c) Ground meristem : It constitute the major part of the apical meristem develops ground tissues like
hypodermis, cortex, endodermis, pericycle, pith and medullary rays.
(iv) According to plane of cell division : On the basis of their plane of cell division meristem are classified
into three categories :
(a) Mass meristem : The cells divide anticlinally in all planes, so mass of cells is formed. e.g., formation of
spores, cortex, pith, endosperm.
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(b) Plate meristem : The cells divide anticlinally in two planes, so plate like area increased. e.g., formation of
epidermis and lamina of leaves.
(c) Rib or File meristem : The cells divide anticlinally in one plane, so row or column of cells is formed.
e.g,, formation of lateral root.
(2) Structure and organisation of apical meristem
(i) Vegetative shoot apex : Shoot apex was first recognized by Wolff (1759) shoot apex is derived from
meristem present in plumule of embryo and occurs at the tip of stem and its branches as terminal bud. It also occurs
in the inactive state in the axils of leaves as lateral buds. The tip of the shoot apex is dome-shaped and from its
flanks at the base of the dome divide to form one or more leaf primordia. This continues throughout the vegetative
phase. Many theories have been put forward to explain shoot apex, such as :
(a) Apical cell theory : This theory was proposed by Nageli (1858). According to this theory, shoot apical
meristem consists of single apical cell. This theory is applicable in case of higher algae, bryophytes and in many
pteridophytes but not in higher plants (i.e., gymnosperms and angiosperms).
(b) Histogen theory : It was proposed by Hanstein (1870). According to this theory, the shoot apical
meristem consists of three distinct meristematic zones or layers (or histogens).
• Dermatogen : Outermost layer and it forms epidermis and epidermal tissue system.
• Periblem : It is the middle layer gives rise to Young leaf Shoot apex
cortex and endodermis.
Axillary Tunica
• Plerome : Innermost layer forms pith and stele. bud Corpus
(c) Tunica corpus theory : This theory was proposed Epidermis
by Schmidt (1924). According to this theory, the shoot apex (Protoderm)
consists of two distinct zones. Procambium
Ground meristem
• Tunica : It is mostly single layered and forms
epidermis. The cells of tunica are smaller than corpus. The Fig : L.S. vegetative shoot apex
tunica shows only anticlinal division and it is responsible for
surface growth.
• Corpus : It represents the central core with larger cells. Corpus shows divisions in all planes and it is
responsible for volume growth.
(ii) Root apex : A group of initial cells, present at the subterminal region of the growing root tip, which is
protected by a root cap is called root apical meristem or root apex. It is embryonic in origin and formed from the
radicle part of embryo. However, in adventitious roots it is produced from derivatives of root apex. The root apex
differs from shoot apex as it is short and more or less uniform due to complete absence of lateral appendages
(leaves and branches) and differentiation of nodes and internodes. According to Hanstein (1870) root apex of most
of the dicotyledons also consists of three meristematic zones - plerome, periblem and dermatogen (fourth meristem
calyptrogen to form root cap only in monocots). Regarding the apical organisation of root following theories have
been put forward.
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(a) Korper-Kappe theory : It was proposed by Schuepp (1917). Procambium
This theory is comparable with the tunica and corpus theory of shoot
apex. Korper means body and Kappe means cap. Protoderm
Cortex Ground
(b) Quiescent centre theory : It was proposed by Clowes (1961). Pith meristem
According to him, in addition to actively dividing cells, a zone of inactive Quiescent
cells is present in the central part of the root apex called quiscent centre. centre
The cells in this region have light cytoplasm, small nuclei, lower Root cap
concentration of DNA, RNA and protein. These cells also contain fewer Fig : L.S. root apical meristem
number of mitochondria, less endoplasmic reticulum and small
dictyosomes.
Types of root apex : It is divided into following four types :
Ranunculus type : Root apex is made up of only one type of histogen layer. e.g., Plants of family -
Ranunculaceae, Leguminosae and Amentiferae.
Casuarina type : Root apex is made up of two types of histogen layers. e.g, Plants of family -
Casurinaceae, Leguminosae and Proteaceae.
Common dicot root : Root apex is made up of three layers of histogen.
Common monocot root : Root apex is made up of four layers of histogen.
(iii) Reproductive apex : During reproductive phase, the vegetative apices Carpels
are converted into reproductive apices. Before conversion, the apex stops
producing leaf primordia. The summit of the apex which remained inactive Stamen
during the vegetative phase, starts dividing. As a result of cell divisions, the apical Petal
meristem undergoes change in shape and increase in size. The apex may develop
into a flower or an inflorescence. When the apex is to develop into a single Sepal
flower, the cells at the flanks of the apex produce sepals and petals while the cells
in the centre of summit produce stamens and carpels. Fig : L.S. Reproductive apex
(diagrammatic)
Permanent tissues.
Permanent tissues are made up of mature cells which have lost the capacity to divide and have attained a
permanent shape, size and function due to division and differentiation
in meristematic tissues. The cells of these tissues are either living or Nucleus
dead, thin-walled or thick-walled. Permanent tissues are of three types :
(1) Simple tissues : Simple tissues are a group of cells which Intercellular space
are all alike in origin, form and function. They are further grouped Vacuoles
under three categories : Cytoplasm
(i) Parenchyma : Parenchyma is most simple and unspecialized
tissue which is concerned mainly with the vegetative activities of the
plant. Fig : Parenchyma in T.S.
The main characteristics of parenchyma cells are :
(a) The cells are thin-walled and soft.
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(b) The cells usually are living and possess a distinct nucleus.
(c) The cells contain well-developed intercellular spaces amongst them.
(d) The cytoplasm is vacuolated and cell wall is made up of cellulose.
(e) The shape may be oval, spherical, cylindrical, rectangular and stellate (star shaped) in leaf petioles of
banana and canna and some hydrophytes.
(f) This tissue is generally present in almost all the organs of plants, i.e., roots, stems, leaves, flowers, fruits and seeds.
(g) If they enclose large air spaces they are called as aerenchyma; if they develop chlorophyll, they are called
as chlorenchyma and if they are elongated cells with tapering ends, they are called as prosenchyma.
Functions : They perform the following functions :
• Storage of food materials. e.g., Carrot, Beetroot etc.
• Chlorenchyma helps in photosynthesis.
• Aerenchyma helps in floating of the aquatic plants (Hydrophytes) and also help in gaseous exchange
during respiration and photosynthesis. e.g., Hydrilla.
• In turgid state they give rigidity to the plant organ.
• In emergency they behave like meristematic cells and help in healing of the various plant injuries.
• Sometimes they store secretory substances (ergastic substance) such as tannins, resins and gums and they
called as idioblasts.
(ii) Collenchyma : The term collenchyma was coined by Schleiden (1839). It is the tissue of primary body.
The main characteristics of are given below : Thickening on corners Uneven
due to deposition of thickened
• The cells of this tissue contain cellulose and pectin
protoplasm and are living. walls
Lumen
• The cell walls are thickened at the
corners and are made up of cellulose,
hemicellulose and pectin.
• They are never lignified but may posses BC
simple pits.
• They are compactly arranged cells, oval,
spherical or polygonal in outline.
• No. intercellular spaces are present. A
Fig : (A) Collenchyma L.S. (B) and (C)T.S. of the same
• The tissue is plastic, extensible and have
capacity to expand.
• They provide mechanical strength to younger part where xylum is less developed.
Collenchyma occurs chiefly in the hypodermis of dicotyledonous stems (herbaceous, climbers or plants e.g.
Cucurbeta, Helianthus) and leaves. They are usually absent in monocots and in roots.
(a) Types of collenchyma : Majumdar (1941) divided collenchyma into three types on the basis of thickening :
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• Angular collenchyma : Where the thickening of the cells is confined to the corners of the cells. e.g.,
Tagetes, Tomato, Datura, Potato, etc.
• Plate or Lamellar collenchyma : When the thickenings are present in the tangential walls. e.g.
hypodermis of sunflower stem.
• Lacunar or Tubular collenchyma : If the thickened cell wall is associated with intercellular spaces of
the adjacent cells. e.g. leaf petioles of compositae and malvaceae etc. hypodermis of Cucurbita stem, Salvia, Malva.
(b) Functions
• Provide mechanical support to petiole, pedicels, branches of stem, roots and fruits.
• If they contain chlorophyll they help in photosynthesis.
• It is present at the margins of some leaves and resists tearing effect of the wind.
(iii) Sclerenchyma : It was discovered and coined by Mettenius (1805).
The main feature of sclerenchyma are :
• It consist of thick-walled dead cells.
• The cells vary in shape, size and origin.
• They possess hard and extremely thick secondary walls due to uniform
deposition of lignin.
• In the beginning the cells are living and have protoplasm but due to deposition
of impermeable secondary walls they become dead.
Types of sclerenchyma : They are of two types :
(a) Sclerenchymatous fibres : These are greatly elongated and tapering at both A
the ends. The fully developed fibre cells are always dead. They are polygonal in
transverse section and walls are highly lignified. Intercellular spaces are absent and
lumen is highly obliterated. The walls show simple and oblique pits. They provide
mechanical strength to the plant. Some of the longest fibre yielding plants are Linum
usitatissimum (Flax or Alsi), Corchorus, Cannabis, etc. The fibres are present in
hypodermis of monocot stem, in pericycle of many dicots, in secondary wood and
vascular bundle sheath in monocot stems. There are three different kinds of fibres :
• Bast fibres : The fibres present in the pericycle (e.g., Cannabis sativa / Hemp B
or Bhang), Linum usitatissimum and phloem (e.g., Corchorus capsularis (Jute), Hibiscus
cannabinus (Patsan), Calotropis, Nerium, Sunn hemp etc.). These fibre are also known Fig : Scalerenchymatous
as extraxylary fibres. fibres (A) L.S. (B) T.S.
• Wood fibres : Those fibres which are associated with wood or xylem have bordered pits are known as
wood fibres. Thick walled wood fibres having simple pits are called libriform fibres whereas thin walled wood-fibres
having bordered pits are called fibre-tracheids. A specific type of wood fibre is produced by Quercus rabra and is
called gelatinous or mucilagenous fibres.
• Surface fibres : The fibres present over surface of plant organs are called surface fibres. e.g. Cotton
fibres found in the testa of seeds, mesocarp fibres of Coconut (Cocus nucifera).
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(b) Stone cells or Sclereids : They are lignified, extremely thick walled so that the lumen of the cells is
almost obliterated and may be spherical, oval, cylindrical, T-shaped and even stellate. They are generally found in
hard parts of the plant, e.g., endocarp of Walnut and
Coconut. They form part of seed coat in some members of
leguminosae. The sclereids provide mechanical support and A Ramiform pit Simple pit D
hardness to the soft parts. Sclereids may be : BC
• Brachy-sclereids or stone cells : These are
small and more or less isodiametric in shape. They occur in
the cortex, pith, phloem, and pulp of fruits (e.g., Pyrus).
• Macrosclereids or rod cells : These are rod- Reduced lumen G
shaped elongated sclereids usually found in the leaves, cortex E
of stem and outer seed coats.
• Osteosclereids or bone cells : These are bone H
or barrel-shaped sclereids dilated at their ends. e.g., leaf of
Hakea. Stone cells
Fig : Stone cells (A, B) from pulp of pear, (C,D) from stem
• Astrosclereids or stellate cells : These are star- cortex of Hoya, (E, F) from petiole of Camelia, (G) from stem
shaped sclereids with extreme lobes or arms. e.g., leaf of cortex of Trochodendron, (H) from mesophyll cells of fig leaf
Nymphaea.
• Trichosclereids or internal hairs : These are hair-like sclereids found in the intercellular spaces in the
leaves and stem of some hydrophytes.
(2) Complex tissues : A group of more than one type of cells having common origin and working together
as a unit, is called complex permanent tissue. The important complex tissues in vascular plants are : xylem and
phloem. Both these tissues are together called vascular tissue.
(i) Xylem : The term xylem was introduced by Nageli (1858). Xylem is a conducting tissue which conducts
water and mineral nutrients upwards from the root to the leaves.
On the basis of origin xylem is of two types
• Primary xylem : It is derived from procambium during primary growth. It consists of protoxylem and
metaxylem.
• Secondary xylem : It is formed from vascular cambium during secondary growth.
Xylem is composed of four types of cells
(a) Tracheids : Term “Tracheids” was given by Sanio (1863). The tracheids are elongated tubelike cells with
tapering or rounded or oval ends with hard and lignified walls.
The walls are not much thickened. The cells are without protoplast and are dead on maturity. The tracheids of
secondary xylem have fewer sides and are more sharply angular than the tracheids of primary xylem. The cell cavity
or lumen of a tracheid is large and without any contents. Tracheids possess bordered pits. Maximum bordered pits
are formed in gymnospermous tracheids. They also possess various kinds of thickenings, e.g., annular, spiral,
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Anatomy of Flowering Plants
scalariform, reticulate or pitted tracheids. All the vascular plants have tracheids in their xylem. The main function of
tracheids is to conduct water and minerals from the root to the leaf. They also provide strength and mechanical
support to the plant. Simple perforation
(b) Xylem vessels or Tracheae : Vessels are rows of plate
elongated tube-like cells, placed end to end with their end walls
dissolved. Vessels are multicellular with wide lumen. The vessels
may be classified into several types according to the thickening
developed in their wall. They may be annular, spiral, Ray
scalariform, reticulate or pitted. Vessels are absent in cells
pteridophytes and gymnosperms (except Ephedra, Gnetum,
Selaginella, Pteridium). In angiosperms (porous wood) vessels Border Simple perforation D
are always present (Vessels are absent in family - Winteraceae, pits plate
Trochodendraceae and Tepacenpaceae of Angiosperm i.e.
A C
Lotus, Wintera, Trochodendron). Vessels along with tracheids
forms the main tissue of xylem of vascular bundles of the E
angiosperms and help in conduction. It also provide mechanical B
support to the plant. Fig : Xylem-A Tracheids, B. Tracheae, C and E. Xylem
parenchyma D. Wood fibres (wood sclerenchyma)
On the basis of distribution and size of vessels, porous wood is of two types :
• Diffuse porous wood (Primitive) : Vessels of same size are uniformly distributed throughout the
growth or annual ring e.g., Pyrus, Azadirachta, Eucalyptus, Mangifera sp., Betula. They are characteristics of plants
growing in tropical region.
• 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, Cassia, Delbergia, Tilea sp.
(c) Wood (xylem) parenchyma : These are the living parenchymatous cells. As found associated with xylem
they are known as wood parenchyma. They serve for the storage of reserve food and also help in conduction of
water upwards through tracheids and vessels.
(d) Wood (xylem) fibres : The long, slender, pointed, dead and sclerenchymatous cells found associated
with xylem are termed wood fibres. They possess mostly thickened walls and few small pits. These pits are found
abundantly in woody dicotyledons. They aid the mechanical strength of xylem and various organs of plant body.
(ii) Phloem (bast) : Term “Phloem” was given by Nageli. Its main function is the transport of organic food
materials from leaves to stem and roots in a downward direction.
On the basis of position phloem is of three types :
(a) External phloem : It is normal type and present outside the xylem e.g., Mostly angiosperms and
gymnosperms.
(b) Internal or Intraxylary phloem : It originates from procambium and is primary phloem which occurs on
innerside of primary xylem. It is primary anamolus structure. e.g., Members of Apocynaceae, Asclepiadaeae,
Convolvulaceae, Solanaceae.
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(c) Induced or Interxylary phloem : It originates from cambium and is secondary phloem which occurs in
groups within the secondary xylem. It is secondary anamolus structure. e.g., Leptadaenia, Salvadora,
Chenopodium, Boerhaavia, Amaranthus.
On the basis of origin phloem is of two types
(a) Primary phloem : It is formed by procambium during primary growth. It may or may not show
differentiation of in protophloem (consists of sieve elements and parenchyma) and metaphloem (develop after
protophloem and consists of sieve elements, parenchyma and fiber). During the primary growth the protophloem
elements are curshed by the surrounding tissues and disappear. This process is known as obliteration consists of
sieve elements, parenchyma and fibre.
(b) Secondary phloem : It is produced during secondary growth by vascular cambium.
It consists of the following elements :
Sieve element
Companion cells
Phloem parenchyma
Phloem fibres or bast fibres
(1) Sieve element
(i) They are long tube-like cells placed end to end, forming a continuous channel in the plant parts.
(ii) Their cell wall is made up of cellulose.
(iii) Their transverse wall is perforated like a normal sieve and hence they are called as sieve tubes.
(iv) Nucleus is not found in these cells.
(v) Each sieve tube has a lining of cytoplasm near its periphery.
(vi) Callus pad may be visible in the winter season.
(vii) Their main function is to translocate the food material from one part to the other.
(2) Companion cells Phloem
parenchyma
(i) They are thin-walled cells which are associated with Sieve plate
sieve tubes.
Callus
(ii) They are more or less elongated.
(iii) They are connected with the sieve tube through B
sieve pore. Companion
cell Sieve
(iv) They contain nucleus and are therefore, living in Sieve area
nature.
tube C D
(v) They are not found in pteridophytes and A
gymnosperms but are always present in angiosperms.
Fig : Parts of Phloem (A) L.S. of phloem tissue, (B) T.S. of
phloem tissue, (C) Sieve tubes of Vitis, (D) L.S. of sieve plate
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(3) Phloem parenchyma : The parenchyma associated with the phloem is called phloem parenchyma. The
cells are elongated with rounded ends and possess cellulosic cell walls. These cells are living and store food reserves
in the form of starch and fats. They are present in pteridophytes and most of dicotyledonous angiosperms. They are
absent in monocots.
(4) Phloem or Bast fibres : The sclerenchymatous fibres associated with the phloem are called as phloem
fibres. These are also known as bast fibres. The fibres are elongated lignified cells with simple pits. The ends of these
cells may be pointed, needle like or blunt. They are non-living cells that provide mechanical support to the organs.
Special or Secretory tissues.
These tissue perform special function in plants, e.g., secretion of resins gum, oil and latex.
These tissues are of two types :
(1) Laticiferous tissues
(2) Glandular tissues
(1) Laticiferous tissues : They are made up of thin walled, elongated, branched and multinucleate
(coenocytic) structures that contain colourless, milky or yellow coloured juice called latex. These occur irregularly
distributed in the mass of parenchymatous cells. latex is contained inside the laticiferous tissue which is of two types :
(i) Latex cells : A laticiferous cell is a very highly branched cell with long slender processes ramifying in all
directions in the ground tissue of the organ. 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 in all directions. At
maturity, they form a highly ramifying system of channels full of latex inside the organ. Plants having such tissues
are called compound or articulated laticifers. e.g., Argemone, Papaver (Papaveraceae), Sonchus (Compositae),
Hevea, Manihot (Euphorbiaceae).
(2) Glandular tissue : This is a highly specialized tissue consisting of glands, discharging diverse functions,
including secretory and excretory. Glands may be external or internal.
(i) External glands : They are generally occur on the epidermis of stem and leaves as glandular hair in
Plumbago and Boerhaavia, stinging hair secrate poisonous substance in Urtica dioica, nectar secreting glands in
flowers or leaves. e.g., Rutaceae and Euphorbiaceae. Digestive enzyme secreting glands in insectivorous plants e.g.,
Drosera (Sundew), Nepenthes (Pitcher plant).
(ii) Internal glands : These are present internally and are of several types. e.g., oil glands in Citrus and
Eucalyptus, resinous ducts in Pinus, mucilage canals in Cycas. Water secreting glands (hydathodes) in Colocasia
(present at the tip of leaves), Tropaeoleum (along margin), etc. The glands which secrete essential oil are called
osmophores (osmotrophs).
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Tissues
Meristematic tissue Permanent tissue
Acc. to origin and Acc. to position Acc. to function Acc. to plane Simple tissue
development of cell division
1. Parenchyma : Cells are
1. Promeristem : 1. Apical meristem : 1. Protoderm : It 1. Mass meristem : Forms living, soft with thin cellulosic wall
Gives rise to primary Responsible for secondary develops into the mass of cell e.g., formation and intercellular spaces. Present
meristem. growth of an organ. of spores, cortex, pith, in all the plant organs e.g., roots,
epidermis or epidermal endosperm etc. stems, leaves, fruit, seeds etc.
2. Primary meristem : tissue system.
Gives rise to primary 2.Intercalary meristem 2. Plate meristem : 2. Collenchyma : Compactly
permanent tissue. : Present at the base of 2. Procambium : Increase plate like area arranged living cells with thick
node (e.g., Mint) or Gives rise to primary e.g. formation of wall of pectin and hemicellulose
internode (e.g., stems of vascular tissue, epidermis and lamina of and no intercellular spaces.
many monocots, i.e. constitute procambium. leaves.
3. Secondary meristem : Wheat, Grasses etc) or at 3. Rib or file meristem :
Produce secondary tissues the base of leaf e.g., Pinus. 3. Ground meristem : Form row or column of
e.g., phellogen or cork cells e.g., formation of
cambium, interfascicular 3. Lateral meristem : Develops ground tissue lateral roots. Angular Plate or Lacunar or
cambium, cambium etc. e.g., hypodermis, cortex,
Increases diameter of endodermis, pericycle, lamellar tubular
an organism. e.g., Tagetus,
pith, medullary rays. Tomato, e.g., hypodermis e.g., hypodermis
of Sunflower of Cucurbita stem.
Datura, stem.
Potato etc.
3. Sclerenchyma : Thick
walled dead cells due to
uniform deposition of lignin.
Sclerenchymatous fibres : Stone cells or tracheids :
Elongated and tapering at May be spherical, oval or
both the ends e.g., Cannabis cylendrical e.g., endocarp of
Sativa, Linum, Corchorus, Walnut and Coconut, occur
Cocus etc. in pulp of some fruits, part of
seed coat.
Complex tissue Special or secretory tissue
Xylem Phloem Glandular tissue : Highly Laticiferous tissue :
Conducting element which specialized tissue consisting
conducts water and mineral Food conducting of glands including Thin walled branched,
nutrients upwards from the secretory or exretory.
root to the leaves. elements which elongated and
1. External glands : Occurs in
1. Tracheids : Elongated transport the organic epidermis of stems and leaves as multinucleate structure
tube like cells with tapering glandular hair in Plumbago and
or rounded or oval ends, food material Boerhaavia, stinging hair secrete that contain latex.
with hard and lignified walls. poisonous substance in Utrica dioica,
e.g., present in xylem of all downward from leaves nector secreting glands in flowers or 1. Latex cells : Very
vascular plant. to stems and roots. leaves of Rutaceae, Euphorbiaceae,
digestive secreting glands in highly branched cell
2. Xylem vessels or trachae : Sieve elements : sectivorous plants e.g., Nepenthes which do not fuse and
Elongated tube like cells, placed (Pitcher plant), Drosera (Sundew). do not form network.
end to end. e.g., always present Nucleus is not found. In e.g.,Calotropis, Nerium,
in angiosperms (except lotus, 2. Internal glands : Present Vinca, Euphorbia, Ficus.
Winifera, Trochodendron) and angiosperm it occurs as internally e.g., oil glands in Citrus
absent in pteridophytes and and Eucalyptus, resinous ducts in
Gymnosperms (except Ephedra, sieve plate while in Pinus, schizogenous canal and
Gnetom, Selaginella Pteridium). mucilage canals in Cycas, water
pteridophytes and secreting glands hydathodes in
3. Wood parenchyma : Colocasia (present at the tip of
Living parenchymatous gymnospermum as leaves); Tropaeoleum (along 2. Latex vessels :
cells associated with xylem. margin), etc. Formed due to fusion of
sieve cells (have nuclei). cells and form network like
4. Wood or xylem fibres :
Long, slender, pointed, dead Companion cells : structure in all directions
and sclerenchymatous. e.g., Contain nucleus. Not found e.g., Argemone Papaver,
found in woody dicotyledons. Sonchus, Hevea, Manihot.
in pteridophytes and
Chapter 16 gymnosperms but always
present in angiosperms.
Phloem parenchyma :
Parenchymatous living cells with
cellulosic cell wall and nucleus. e.g.,
present in pteridophytes and some
of dicotyledonous angiosperms but
absent in monocotyledons.
Phloem or Bast fibres :
Sclerenchymatous fibres
associated with phloem
abundantly found in sec.
phloem e.g., Jute, Hamp.
229
Anatomy of Flowering Plants
The tissue system.
The various types of tissues present in the body of a plant perform different functions. Several tissues may
collectively perform the same function. A collection of tissues performing the same general function is known as a
“Tissue System''. According to Sachs (1975) there are three major tissue systems in plants as follows :
(1) Epidermal tissue system (2) Ground or fundamental tissue system (3) Vascular tissue system
(1) Epidermal tissue system : The tissues of this system originate from the outermost layer of apical
meristem. It forms the outermost covering of various plant organs which remains in direct contact with the
environment.
(i) Epidermis : Epidermis is composed of single layer cells. These cells vary in their shape and size and form
a continuous layer interrupted by stomata. In some cases epidermis may be multilayered e.g. Ficus, Nerium,
Peperomia, Begonia etc.
The epidermal cells are living, parenchymatous, and compactly arranged without intercellular spaces.
Certain epidermal cells of some plants or plant parts are differentiated into variety of cell types :
(a) In aerial roots, the multiple epidermal cells are modified to velamen, which absorb water from the
atmosphere (e.g., Orchids).
(b) Some of the cells in the leaves of grasses are comparatively very large, called bulliform or motor cells. It
is hygroscopic in nature. e.g., Ammophila. They are thin-walled and contain big central vacuoles filled with water.
They play an important role in the folding and unfolding of leaves.
(c) Some members of Gramineae and Cyperaceae possess two types of epidermal cells : the long cells and the
short cells. The short cells may be cork cells or silica cells.
(ii) Cuticle and Wax : In aerial parts, epidermis is covered by cuticle. The epidermal cells secrete a waxy
substance called cutin, which forms a layer of variable thickness (the cuticle) within and on the outer surface of its all
walls. it helps in reducing the loss of water by evaporation. Usually the cuticle is covered with wax which may be
deposited in the form of granules, rods, crusts or viscous semiliquid masses. Other substances deposited on the
cuticle surface may be oil, resin, silicon and salts (cystoliths are crystals of calcium carbonate, e.g., Ficus. Druse and
Raphides, e.g., Pistia) are crystals of calcium oxalate. Thick cuticle are found in leaves of dry habitats plants.
(iii) Stomata : Stomata are minute apertures in the epidermis. Each aperture is bounded by two kidney
shaped cells, called guard cells. Stomata are absent in roots. In xerophytes the stomata are sunken in grooves due to
which rate of transpiration is greatly reduced (e.g. Nerium). Usually there is a large air cavity below each aperture, it
is called substomatal cavity. In some species the guard cells are surrounded by subsidiary cells or accessory cells
which differ morphologically from the other epidermal cells. In monocots e.g., Doob, Maize guard cells are dumb
bell shape. Stomata are scattered in dicots leaves but they are arranged in rows in monocots.
Depending upon distribution of stomata, the leaves are :
(a) Apple-mulberry type : e.g. Oxalis, Mulberry, Apple.
(b) Potato type : e.g. Bifacial (dorsiventral leaves of pea, bean, tomato).
(c) Oat type : e.g. Suberect (isobillateral) leaves of most grasses and cereals (monocotyledens).
Chapter 16 230
Anatomy of Flowering Plants
(d) Nymphea type : e.g. Floating leaves of Nelumbo, Nymphia, water lily.
(e) Potamogeton type : e.g. Submerged plants like Hydrilla, Vallisneria, Potamogeton.
(iv) Trichomes : These are epidermal outgrowths A
present temporarily or permanently on almost all plant parts.
They may be unicellular or multicellular and vary in size and E
shape in different species. They may be of different types :
stellate hair, glandular hair, short glandular hair, floccose hair,
urticating hair and stinging hair.
The trichomes serve for checking excess loss of water C
and for protection. G
(v) Root hairs : They are enlargements of special B DF
epiblema cells called trichoblasts and occurs in a particular
zone of young root called root hair zone. A root hair cell has Fig : Appendages of epidermis of leaves
vacuolated protoplast with nucleus present towards the apical A. Stellate hair of Alyssum, B. Glandular hair of
part of hair. They are specialised to absorb water from soil Pelorgonium C. Short glandular hair of lavandula, D.
crevices. They also hold soil particles. Floccose hair of Malva, E. Glandular hair of Solanum,
F. Urticating hair of Verbascum, G. Stinging hair of Cestus
(2) Ground or Fundamental tissue system : Ground tissue system includes all the tissues of plant body
except epidermal tissue system and vascular tissues. It forms the bulk of body. This tissue system mainly originates
from ground meristem. The ground tissues constitute the following parts :
(i) Cortex : It lies between epidermis and the pericycle. The cortex is distinct in dicotyledons but not in
monocotyledons where there is no clear demarcation between cortex and pith. 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. Its main function is storage of food.
(c) Endodermis (Starch sheath) : It is mostly single layered and is made up of parenchymatous barrel
shaped compactly arranged cells. The inner and radial or transverse wall of endodermal cells have casparian strips
of suberin. In roots thick walled endodermal cells are interrupted by thin walled cells just outside the protoxylem
pathches. These thin walled endodermal cells are called passage cells or transfusion cells. A fully developed
endodermis is found in all types of roots. Endodermis with characteristic casparian bands is absent in woody dicot
stem, monocot stem and leaves of angiosperms. The young stems of angiosperms show a layer with abundant
starch deposition. This layer occurs in the position where endodermis would have been situated which is called as
starch sheath. In Selaginella trabeculate endodermis is found due to formation of air spaces between two
endodermal cells.
Endodermis behave as water tight dam to check the loss of water and air dam to check the entry of air in
xylem elements. Endodermis is internal protective tissue.
(ii) Pericycle : It is a single layered or multilayered cylinder of thin-walled or thick-walled cells present
between the endodermis and vascular tissues. In some cases, the pericycle is made up of many layers of
sclerenchymatous cells (Cucurbita stem) or in the form of alternating bands of thin-walled and thick-walled cells
(Sunflower stem). In case of roots, the pericycle is made up of thin-walled parenchymatous cells which later on gives
Chapter 16 231
Anatomy of Flowering Plants
rise to lateral roots. In dicot roots the cork cambium originates in the pericycle which results in the formation of
periderm. Pericycle also gives rise to a part of vascular cambium in dicot roots.
(iii) Pith or Medulla : It occupies the central part in dicot stem, and monocot root. It is mostly made up 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 known as primary medullary rays or pith rays.
They help in lateral translocation.
(3) Vascular tissue system : The central cylinder of the shoot or root surrounded by cortex is called stele.
The varying number of vascular bundles formed inside the stele constitute vascular tissue system. Xylem, phloem
and cambium are the major parts of the vascular bundle. Vascular bundle may be of following types :
(i) Radial : The xylem and phloem strands alternate with each other separated by parenchymatous cells. such
kinds of vascular bundles are called radial and found mainly in roots.
(ii) Conjoint : A vascular bundle having both xylem and phloem together, is called conjoint. Normally the
xylem and phloem occur in the same radius. They occur in stems. Such vascular bundles are of two types :
(a) Collateral : A vascular bundle in which the phloem lies towards outerside and xylem towards inner side,
is called collateral, e.g., Sunflower.
Collateral bundle having a cambium between xylem and Conjoint
phloem is said to be of the open type, e.g., Dicot stem.
Collateral Open Bicollateral
Collateral bundle lacking a cambium between xylem and Closed Outer
phloem is said to be of the closed type, e.g., Monocot stem. phloem
Phloem Outer
(b) Bicollateral : A vascular bundle having the phloem Cambium cambium
strands on both outer and inner side of xylem, is called bicollateral. Xylem
e.g., Cucurbita. Xylem Inner
cambium
(iii) Concentric : A vascular bundle in which one tissue is Concentric
completely surrounded by the other, is called concentric. The Inner
concentric bundles are of two types : phloem
(a) Amphivasal (Leptocentric) : The phloem lies in the Radial
centre and remains completely surrounded by xylem. e.g.,
Dracaena, Yucca. Amphivasal Amphicribral
Phloem
Phloem
Xylem Xylem
Fig : Different types of vascular bundles
(b) Amphicribal (Hadrocentric) : The xylem lies in the centre and remains completely surrounded by
phloem. e.g., Ferns.
Stelar system
Stelar theory was proposed by Van Tieghem and Douliot (1886). According to this concept primary body of
root and stem are basically alike anatomically i.e. each consists of a central stele surrounded by cortex. Stele
Chapter 16 232
Anatomy of Flowering Plants
includes the vascular tissues and the ground tissue like pericycle and pith, when present. Different types of steles
were recognised, a brief review of which are given in table :
Types of stele Diagrammatic representation
(1) Protostele : This term was given by Endodermis Pericycle
Jeffrey. It is the simplest and most primitive
type of stele in which central core of xylem Phloem
surround by phloem. Xylem
(i) Haplostele : It consists of a smooth core of Leaf trace
xylem which is surrounded by a ring of
phloem. e.g., Rhynia, Selaginella, Lyco Phloem Endodermis
podium, etc. Xylem
(ii) Actinostele : Protostele having star Leaf trace
shaped xylem core with many radiating arms
called actinostele. e.g. Psilotum, Lycopodium
etc. It may be of two types :
(a) Plectostele : A protostele in which xylem Phloem Xylem
core broken into a number of parallel plates is Leaf trace
known as plectostele. e.g., Lycopodium
clavatum.
(b) Mixed protostele : A protostele in which Endodermis Parenchyma
xylem broken into small group or patches is Pericycle
known as mixed protostele. e.g., Lycopodium
cernuum, Hymenophyllum demissum, etc. Xylem
Phloem
(2) Siphonostele : A protostele with central Xylem Phloem
pith is called siphonostele or medullated stele. It Endodermis
is considered to be derived phylogenetically
from protostele and thus represents an advance
form. It is of two types :
(i) Ectophloic siphonostele : When phloem
occurs on the outer side of xylem. e.g.,
Osmunda.
Chapter 16 233 Leaf trace Pith
Anatomy of Flowering Plants
(ii) Amphiphloic siphonostele : When Outer Outer
phloem is present on both external and internal phloem endodermis
sides of the xylem. e.g., Marsilea, Adiantum.
Xylem
Modification of siphonostele
(i) Solenostele : A siphonostele with non- Pith
overlapping leaf gaps is known as solenostele. It Inner
may be ectophloic or amphiphloic. phloem
Inner
(ii) Dictyostele : A siphonostele with endodermis
overlapping leaf gaps is known as dictyostele. It
has many scattered vascular strands called as Phloem
meristeles. e.g., Dryopteris, Pteris Leaf gap
Ophioglossum.
Pith
(iii) Polycyclic stele : When vascular tissue is
present in the form of two or more concentric Leaf trace
cylinders. e.g., Pteridium, aquilinum, Marattia.
It may be polycyclic solenostele or polycyclic Inner Xylem Outer
dictyostele. phloem pericycle
(iv) Polysteles : Somtimes more than one Leaf gap
steles are present in the axis of some
pteridophytes. e.g., 2 steles in Selaginella Leaf trace
kraussiana, 16 steles in S. laevigata.
Pith
Outer
endodermis Inner Outer
endodermis phloem
Meristeles Leaf gap Solenostelic
cylinder
Leaf trace Siphonostelic
Leaf trace cylinder
steles
Internal structure of root, stem and leaf.
(1) Functions of different organs and tissues of a plant tissue system
Chapter 16 234
Anatomy of Flowering Plants
Roots Stems Leaves
(i) Functions (i) Absorb water and minerals. (i) Transport water and nutrients. Carry on photosynthesis.
(ii) Anchor plant. (ii) Support leaves.
(iii) Store materials. (iii) Help store materials.
(ii) Tissues
(a) Epidermis Root hairs absorb water and minerals. Protect inner tissues. Stomata carry on gas exchange.
(b) Cortex Store products of photosynthesis and Carry on photosynthesis if green.
water.
(c) Endodermis Regulates passage of minerals into Regulates passage of minerals also Regulate passage of minerals into
vascular cylinder. into vascular tissue, if present. vascular tissue if present.
(d) Vascular Transport water and nutrients. Transport water and nutrients. Transport water and nutrients.
(e) Pith Store products of photosynthesis and Store products of photosynthesis.
water.
(f) Mesophyll
(i) Spongy layer Carry on gaseous exchange and
(ii) Palisade layer photosynthesis.
(2) Difference between internal structure of root and stem
Description Root Stem
Epidermis usually with cuticle.
(i) Epidermis or Epiblema Epiblema or piliferous layer without cuticle. Multicellular.
Usually present in young stems but absent in old
(ii) Hairs Unicellular. stem.
Poorly developed or absent.
(iii) Chlorenchyma in cortex Absent. Conjoint collateral or bicollateral or concentric.
Endarch.
(iv) Endodermis Very distinct.
(v) Vascular bundle Radial.
(vi) Xylem Exarch.
Origin of Lateral roots : Lateral roots arise endogenously i.e., form the cells inside the endodermis. They
arise from pericycle cells.
(3) Difference between dicot and monocot leaf
Character Dicot leaf Monocot leaf
(i) Type of leaf Dorsiventral (bifacial).
(ii) Stomata Usually more on lower epidermis. Isobilateral.
(iii) Mesophyll Made up of two types of tissues Equal on lower and upper epidermis
(a) Palisade parenchyma. (amphistomatic).
Only spongy parenchyma is present which
has very small intercellular spaces.
Chapter 16 235
Anatomy of Flowering Plants
(b) Spongy parenchyma with large intercellular
spaces.
(iv) Bundle sheath Made up of parenchyma. Just above and below the Made of parenchyma but just above and
(v) Bulliform or motor cells vascular bundle some parenchymatous cells or below the vascular bundles are found
collenchymatous cells are present (upto epidermis). sclerenchymatous cells (upto epidermis).
Absent. Present on upper epidermis.
Bundle Xylem Cuticle Upper Bulliform Cells Cuticle Stoma
sheath epidermis
Mesophyll Substomatal
tissue chamber
Xylem
Bundle
sheath
Lower Phloem
epidermis
Sclerenchyma Phloem Stoma Stoma Sclerenchyma
Air Spaces
Dicot leaf Monocot leaf
Fig : Comparison of T.S. of a dicot and monocot leaf
Kranz type anatomy occurs in both monocot and dicot leaves of some tropical and arid areas. Karanz anatomy
is characteristic feature of C4 plants. The mesophyll is undifferentiated and occurs in concentric layers around
vascular bundles. Cells of bundles sheath posses large chloroplast.
(4) Difference between dicot and monocot stem
Characters Monocotyledonous Stem Dicotyledonous Stem
(i) Epidermis
Present, cells comparatively smaller and Present, cells larger and with hair
(ii) Hypodermis without hair.
(iii) Cortex
Sclerenchymatous (non-green) Collenchymatous (green)
(iv) Endodermis
Absent, but ground tissue is present from Made up of several layers of parenchymatous
(v) Pericycle
hypodermis to the centre of stem tissue.
(vi) Medullary rays
(vii) Pith (Medulla) Absent One layered, starchy sheath which is usually not
well differentiated.
(viii) Vascular bundles
Absent Made up of 1 or more layers of parenchymatous
and sclerenchymatous cells.
Absent Found in between vascular bundles
Absent Abundant, made up of parenchymatous cells
situated in the centre of stem.
Scattered Vascular bundles in a ring
Conjoint, Collateral and closed Conjoint, collateral and open
Chapter 16 236
Anatomy of Flowering Plants
Larger towards centre All of same size
Oval Usually wedge–shaped
Bundle sheath present Bundle sheath absent
Phloem parenchyma absent Phloem parenchyma present
Xylem vessels either Y or V shaped Xylem vessels more radial
Multicellular hair
Cuticle
Epidermis
Hypodermis
Cortex
Pericycle
Phloem
Xylem
Pith
Medullary ray
Cambium
Endodermis
Hypodermis
Monocot stem Epidermis Dicot stem
Cuticle
Fig : Cmparision of the T.S. of monocot and dicot stem
(5) Difference between dicot and monocot root
Character Dicot Root Monocot Root
(i) Pericycle Gives rise to secondary roots and lateral meristem Gives rise to lateral roots only
(ii) Vascular bundles Diarch to hexarch Hexarch to polyarch
(iii) Cambium Develops at the time of secondary growth Absent
(iv) Pith Absent or poorly developed Abundant and fully developed
(v) Secondary growth Takes place Does not take place
Narrow cortex. Endodermis is less thickened and Cortex wide. Casparian strips are visible
casparian strips are more prominent. only in young root. Later on endodermal
cells become highly thickened.
Chapter 16 Root hair
Cortex
Protoxylem
Phloem
Metaxylem
Pith
Pericycle
Endodermis
Ep2ibl3em7a
Monocot root Dicot root
Anatomy of Flowering Plants
Secondary growth.
The increase in thickness or girth due to the activity of the cambium and the cork cambium is known as
secondary growth.
(1) Secondary growth in stem : On the basis of the activities of cambium and cork-cambium, secondary
growth in stem can be discussed under the following heads :
(i) Activity of cambium (ii) Activity of cork-cambium
(i) Activity of cambium : The vascular cambium in between xylem and phloem is called intrafascicular or
fascicular cambium which is primary in origin. At the time of secondary growth the parenchymatous cells of
medullary rays between the vascular bundles become meristematic and form strip of cambium called as
interfascicular cambium which is secondary in origin. Both inter and intrafascicular cambium joins together and
form cambium ring which is partly primary and partly secondary in origin. By anticlinal divisions the
circumference of the cambium increase. By periclinal division cambium produced the secondary xylem and
phloem tissues on innerside and outerside. The amount of sec. xylem produced is 8-10 times greater than sec.
phloem. The cambium has two types of cells :
(a) The fusiform initials which are elongated and form fibres, sieve cells, sieve tubes, tracheids.
(b) Ray initials which produce parenchyma cells of the rays in wood and phloem. Ray initials are much
shorter than fusiform initials. Certain cells of cambium form some narrow bands of living parenchyma cells passing
through secondary xylem and secondary phloem and are called secondary medullary rays. These provide radial
conduction of food from the phloem, and water and mineral salts from the xylem.
• Annual rings : Activity of cambium is not uniform in those plants which grow in the regions where
favourable climatic conditions (spring or rainy season) alternate regularly with unfavourable climatic conditions
(cold water or dry hot summer). In temperate climates, cambium becomes more active in spring and forms greater
number of vessels with wider cavities; while in winter it becomes less active and forms narrower and smaller vessels.
The wood formed in the spring is known as spring wood and that formed in the dry summer or cold winter
autumn wood or late wood. Both autumn and spring wood constitute a growth or annual ring. In one year only
one growth ring is formed. Thus by counting the number of annual rings in the main stem at the base we can
determine the age of a tree. This branch of science is known as dendrochronology. Age is determined by an
instrument increment borer. Growth rings are distinct or sharply demarcated in the plants of temperate regions
where as in tropical climate (near equator) they are not distinct or sharply demarcated in the trees.
(ii) Activity of cork cambium : Cork cambium or phellogen develops from outer layer of cortex. It
produces secondary cortex or phelloderm on innerside and cork or phellum on outerside. The cells of phellem are
dead, suberized and impervious to water. Cells of phelloderm are thin walled, living and store food. Phellem,
Chapter 16 238
Anatomy of Flowering Plants
phellogen and phelloderm collectively called as periderm. Periderm is secondary protective tissue. Due to pressure
of secondary xylem, epidermis raptures and cortex is largely lost after two or three years of secondary growth.
(a) Bark : All dead tissues lying outside the active cork-cambium are collectively known as bark. This includes
ruptured epidermis, hypodermis and cork. When cork-cambium appears in the form of a complete ring, it is known
as ring bark, e.g., Betula (Bhojpatra). If the cork cambium occurs as separate strips and the resulting bark appears
in the form of scales, such a bark is known as scaly bark. e.g., Eucalyptus, Psidium guava. The outermost layer of
bark is dead and called as rhytidome.
(b) Lenticels : These are aerating pores formed in the cork through which gaseous exchange takes place.
They are formed as a result of the action of phellogen. Promeristem Provascular Ground Epidermis
A lenticel appears as a scar or protrusion on the surface (cells all alike) tissue meristem Cortex
of the stem and consists of a radial row of thin-walled B Primary
cells, known as complementary cells or filling A CPahmlobeimum
tissue. They are found in old dicot stem, main (fascicular)
function is guttation. Primary
Xylem
C
(c) Cork : It consists of dead cells with thick walls Epidermis
heavily impregnated with suberin. These cells are Cortex
compactly arranged in radial rows without intercellular Pimary phloem
spaces. Cork is impervious to water and prevents its
loss from the plant surface. It also protects the inner Cambium
tissues from the attack of fungi and insects. There is no (interfascicular)
differentiation of bark, sap wood and heart wood of
Date palm. Pimary xylem
(d) Heart wood and sap wood : In old trees, Secondary xylem
secondary wood is differentiated into a centrally
situated darker and harder wood called the heart Secondary phloem
D Cork E
Phellogen Cortex
First year Secondary
Second year phloem
Third year
Cambium
Primary xylem
Primary phloem
wood or duramen which are physiologically inactive First year Secondary
(almost dead)and an outer light-coloured zone called Second year xylem
the sap wood or alburnum which are physiologically Third year
F
active. Dark colour of heart wood is due to the Fig : Stages of secondary growth in stem
deposition of tannins, resins, gums, essential oils, etc. in
the cell walls and cell cavities. The water conduction takes place through sap wood. During the conversion of sap
wood into heartwood the most important change is development of tyloses in the heart wood. Tyloses are ballon
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 plant. As a tree grows older thickness of heartwood increases and
sap wood remains same.
Tylosis
Chapter 16 Pit 239 Periderm
Phloem
Xylem Sap wood
parenchyma Heart wood
Xylem
vessel
Anatomy of Flowering Plants
(2) Secondary growth in dicot roots : Vascular bundles in dicot roots are radial, exarch and mostly triarch.
Vascular cambium is formed secondarily from conjuctive parenchyma cells lying just below each phloem strand.
Thus the number of cambium strips formed equals the number of phloem strands. The cells of pericycle lying
outside the protoxylem also become 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 produced
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 inner side.
Formation of Cortex Periderm Medullary ray
cambium Epidermis Primary phloem
Primary xylem Secondary
phloem
Cambium
Secondary
xylem
Primary phloem Primary xylem
Fig : Secondary growth in dicot root
Important Tips
• N.Grew is the father of anatomy (1682) and coined the term tissue and parenchyma.
• Haberlandt proposed the names of protoderm (for dermatogen), ground meristem (for periblem) and procambium (for plerome)
• Haberlandt (1914) gave the terms lepton for soft walled conducting part of phloem and hadrom for conducting part (tracheary
elements) of xylem.
• Strasburger discovered albuminous cells instead of companion cells in the phloem of non-flowering plants.
• In sugarcane there is no distinction of tunica and corpus.
• Reproductive apex is elongated in Sagittaria but it can be 400 times broad in Chrysanthemum.
• Seive cells or seive tube elements resemble RBCs in being without nucleus in the mature state.
• Cavities are of three types :
(i) Schizogenous : They are formed by enlargement of intercellular spaces or separation of cells e.g. oil of Sunflower.
(ii) Lysigenous : They are formed by degeneration of cells, e.g., oil cavity of Citrus and protoxylem lacunae or water cavity in
monocot stem vascular bundles.
(iii) Schizolysigenous : They are formed partly by separation and partly by degeneration of cells. e.g., protoxylem cavity.
• Pith cavity often present in monocot stems (e.g., grass) and occassionally in dicot stems (e.g., Ricinus).
Chapter 16 240
Anatomy of Flowering Plants
• Wood without vessels is called homoxylous, e.g., Ranales (winteraceae, tetracentraceae, trochodendraceae). Whereas with vessels is
called heteroxylous.
• The wood of Tactona grandis is termite resistance.
• The bottle cork is prepared from cork of Quercus suber (Oak tree).
• Lightest wood is of Ochroma pyramidate (O.lagopus).
• Heaviest wood is of Guaiacum officinale. In India heaviest wood is of Acacia sundra.
• Most durable soft wood is of Cedrus deodara.
• Latex for chewing or chickle gum obtained from Achras sapota, Gutta percha (insulating material) from palaquium gutta alkaloid opium
from Papaver sominiferum (poppy), papain (enzyme) from carica papayas, Rubber from Hevea brasiliensis, Ficus elastica.
• Reaction wood is a wood formed in bending stems. When reaction wood is formed on the lower side, it is called as Compression wood
e.g., conifers. When it is formed on the upper side, it is called as tension wood e.g., Dicots.
• Wound periderm is similar to natural periderm. But it is restricted to the place of injury and is used in producing the commercial cork.
• Maceration is a method of separation of various tissues by disintegration of middle lamella.
• In some plants primary structure is abnormal such as presence of medullary bundles in pith e.g., Boerhaavia, Mirabilis, Achyranthes,
Bougainvillea or presence of cortical vascular bundles (inverted) e.g., Casuarina and Nyctanthus.
• A protective tissue found in roots of some plants (Rosaceae, Myrtaceae) having alternate layers of endodermal and parenchyma cells are
called periderm.
• Knots are the bases, scars/wounds of fallen branches get covered by growth of secondary tissues. They form knots in the wood.
• Abscission is a special layer of parenchymatous cells appears at the base. Abscission is premature fall of plant parts from the plant
without causing the injury. A protective layer of suberised thick walled cork cells is formed below the abscission layer to prevent infection
or dessication (sometimes it is corky layer).
• Metaxylem consist of two larger and rounded vessels situated on the sides with the pitted tracheids in between them.
• Protoxylem consists of two smaller vessels situated to wards the centre. The vessels of metaxylem are pitted and those of protoxylem are
annular and spiral.
• Depending upon the relative position of protoxylem; xylem is of four types :
(i) Exarch : Protoxylem towards the outerside.
(ii) Endarch : Protoxylem towards innerside of metaxylem.
(iii) Mesarch : Protoxylem surrounded by metaxylem.
(iv) Centrach : Protoxylem in the centre of metaxylem.
• Endarch xylem is also called centrifugal as xylem matures from inside to outside. Similarly, exarch xylem is known as centripetal
because differentiation of xylem proceeds from outside to inside e.g. roots.
• Root cap is absent in hydrophytes.
• Root hairs are found in zone of maturation.
• In the leaf, vascular bundles are found in the veins.
• An example of monocots showing secondary growth in stems is Yucca or Draceana.
• Safranine stains lignified elements of the tissue.
• The longitudinal section of a root have four zones which occur in the following order (from the tip upward) : Root cap, cell division, cell
enlargement, cell maturation.
Chapter 16 241
BOTANY
CHAPTERS 17-19
BOOKLET-3
Contents: Page No.
Chapter 17 Transport in Plants 242-283
Chapter 18 Mineral Nutrition 284-310
Chapter 19 Photosynthesis in Higher Plants 311-341
Transport in Plants
Introduction.
Plant physiology (Physis = nature of life; logas = study) is the branch of botany which deals with the study of
life activities of plants. It include the functional aspects of its processes both at cellular as well as sub-cellular level.
Life process or physiological process may be defined, as any chemical or physiological change occuring within
a cell and organism and any exchange of substances between the cell or organism and its environment.
According to the definition of physiological process, imbibition, osmosis, diffusion, plasmolysis, water
potential, water conduction, ascent of sap, transpiration, solute absorption and translocation, transport of radiant
energy, photomorphogenetic responses, etc. are considered as physiological processes.
Concept of water relation.
Water is the most important constituent of plants and is essential for the maintenance of life, growth and
development. Plants lose huge amount of water through transpiration. They have to replenish this lost water to
prevent wilting. Water is mainly absorbed by the roots of the plants from the soil, than it moves upward to different
parts and is lost from the aerial parts, especially through the leaves. Before taking up the absorption and movement
of water in plants, it is worthwhile to understand the phenomenon of imbibition, diffusion and osmosis involved in
the water uptake and its movement in the plants.
(1) Imbibition : The process of adsorption of water by solid particles of a substance without forming a
solution is called 'imbibition'. It is a type of diffusion by which movement of water take place along a diffusion
gradient. The solid particles which adsorb water or any other liquid are called imbibants. The liquid which is
imbibed is known as imbibate. Cellulose, pectic substances, protoplasmic protein and other organic compound in
plant cells show great power of imbibition.
(i) Characteristics of imbibition : The phenomenon of imbibition has three important characteristics :
(a) Volume change : During the process of imbibition, imbibants increase in volume. It has been observed
that there is an actual compression of water. This is due to arrangement of water molecules on surface of imbibant
and occupy less volume than the same molecules do when are in free stage in the normal liquid. During the process
of imbibition affinity develops between the adsorbant and liquid imbibed. A sort of water potential gradient is
established between the surface of adsorbant and the liquid imbibed.
e.g. If a dry piece of wood is placed in water, it swells and increases in its volume. Similarly, if dry gum or
pieces of agar agar are placed in water, they swell and their volume increases. Wooden doors and windows adsorb
water in humid rainy season and increase in their volume so that they are hard to open or close, in gram and wheat
the volume increase by adsorption of water, in plant systems are adsorption of water by cell wall.
(b) Production of heat : As the water molecules are adsorbed on the surface of the imbibant, their kinetic
energy is released in the form of heat which increase the temperature of the medium. It is called heat of wetting (or
heat of hydration). e. g., during kneading, the flour of wheat gives a warm feeling due to imbibition of water and
consequent release of heat.
(c) Development of imbibitional pressure : If the imbibing substance (the imbibant) is confined in a
limited space, during imbibition it exerts considerable pressure. The bursting of seed coats of germinating seeds is
the result of imbibition pressure developed within the seeds as they soak the water. Imbibition pressure can
be defined as the maximum pressure that an imbibant will develop when it is completely soaked in pure water.
Chapter 17 242
Transport in Plants
Imbibition pressure is also called as the matrix potential because it exists due to the presence of hydrophilic
substances in the cell which include organic colloids and cell wall.
Resurrection plants of Selaginella, lichens, velamen roots and dry seeds remain air dry for considerable
periods because they can absorb water from the slight downpour by the process of imbibition.
(ii) Factors influencing the rate of imbibition
(a) Nature of imbibant : Proteins are the strongest imbibants of water, starch less strong, cellulose being the
weakest. That is why proteinaceous pea seeds swell more than the starchy wheat seeds. During seed germination
seed coat rupture first because it is made up of cellulose (weak imbibant) and kernel is made up of protein, fat and
starch (strong imbibant).
(b) Surface area of imbibant : If more surface area of the imbibant is exposed and is in contact with liquid,
the imbibition will be more.
(c) Temperature : Increase in temperature causes an increase in the rate of imbibition.
(d) Degree of dryness of imbibant : If the imbibant is dry it will imbibe more water than a relatively wet
imbibant.
(e) Concentration of solutes : Increase in the concentration of solutes in the medium decreases imbibition
due to a decrease in the diffusion pressure gradient between the imbibant and the liquid being imbibed. It is due to
the fact that imbibition is only a special type of diffusion accompanied by capillary action. If some solute is added
into the liquid which is being imbibed, its diffusion pressure decreases and the process of imbibition slows down.
(f) pH of imbibant : Proteins, being amphoteric in nature, imbibe least in neutral medium. Towards highly
acidic or highly alkaline pH, the imbibition increases till a maximum is reached, there after it starts slowing down.
(iii) Significance of imbibition
(a) The water is first imbibed by walls of root hairs and then absorbed and helps in rupturing of seed coat
(made up of cellulose).
(b) Water is absorbed by germinating seeds through the process of imbibition.
(c) Germinating seeds can break the concrete pavements and roads etc.
(d) The water moves into ovules which are ripening into seeds by the process of imbibition.
(e) It is very significant property of hydrophilic surfaces.
(2) Diffusion : The movement of the molecules of gases, liquids and solutes from the region of higher
concentration to the region of lower concentration is known as diffusion.
Or
Diffusion is the net movement of molecules or ions of a given substance from a region of higher concentration
to lower one by virtue of their kinetic energy.
Or
It is the movement of molecules from high diffusion pressure to low diffusion pressure.
Chapter 17 243
Transport in Plants
Phenomenon of diffusion can be observed everyday.
It may occur between gas and gas (e.g., diffusion of ammonia into air), liquid and liquid (e.g., diffusion of
alcohol into water), or solid and liquid (e.g., diffusion of sugar into water). The diffusion of one matter is dependent of
other. That is why many gases and solutes diffuse simultaneously and independently at different rates in different
direction at the same place and time, without interfering each other. From soil, water and ions of simple inorganic salts
pass into plants through the root cells by a process which is basically diffusion, though greatly modified by other
factors. The water and solutes pass through the dead and living vessels and also from cell to cell by diffusion. When a
crystal of copper sulphate is placed in a beaker containing water, a dense blue colour is seen around the crystal.
(i) Diffusion pressure : It is a hypothetical term coined by Meyer (1938) to denote the potential ability of
the molecules or ions of any substance to diffuse from an area of their higher concentration to that of their lower
concentration. Alternatively, it may also be defined as the force with which the diffusing molecules move along the
concentration gradient.
(ii) Diffusion pressure deficit (DPD) or Suction pressure (SP) : The term diffusion pressure (DP) and
diffusion pressure deficit (DPD) were putforth by B.S. Meyer in 1938. Originally, the DPD was described by the
term suction force (Saugkraft) or suction pressure (SP) by Renner (1915). Now a days, the term water potential (ψ)
is used which is equal to DPD, but negative in value.
Each liquid has a specific diffusion pressure. Pure water or a pure solvent has the maximum diffusion pressure. If
some solute dissolved in it, the water or solvent in the resulting solution comes to attain less diffusion pressure than
that of the pure water or pure solvent. In other words, diffusion pressure of a solvent, in a solution is always lower than
that in the pure solvent. 'The amount by which the diffusion pressure of water or solvent in a solution is lower than that
of pure water or solvent is known as diffusion pressure deficit (DPD)'. Because of the presence of diffusion pressure
deficit, a solution will always tend to make up the deficit by absorbing water. Hence, diffusion pressure deficit is the
water absorbing capacity of a solution. Therefore, DPD can also be called suction pressure (SP).
(iii) Factors influencing rate of diffusion
(a) Temperature : Increase in temperature leads to increase in the rate of diffusion.
(b) Pressure : The rate of diffusion of gases is directly proportional to the pressure. So the rate of diffusion
increases with increase of pressure. Rate of diffusions ∝ pressure.
(c) Size and mass of diffusing substance : Diffusion of solid is inversely proportional to the size and mass
of molecules and ions.
Rate of diffusion ∝ Size × 1 particles
Mass of
(d) Density of diffusing substance : The rate of diffusion is inversely proportional to the square root of
density of the diffusion substance. Larger the molecules, slower will be the rate of diffusion. This is also called
Graham's law of diffusion.
D∝ 1 (D = Diffusion and d = Density of diffusing substance).
d
According to the density the diffusion of substances takes place in following manner –
Gas > Liquid > Solid
Chapter 17 244
Transport in Plants
The vapours of volatile liquids (sent or petrol) and solids (camphor) also diffuse like gases.
(e) Density of the medium : The rate of diffusion is slower, if the medium is concentrated. Thus, a gas
would diffuse more rapidly in vacuum than in air. Substances in solution also diffuse but at a much slower rate than
gases. Substances in solution diffuse more rapidly from regions in which their concentration is higher into regions of
low concentration. If two solutions of sugar (or of any other substance) of different concentrations are in contact,
sugar molecules diffuse from the higher to the lower concentrations of sugar and water molecules diffuse from the
higher to the lower concentrations of water, until equilibrium is attained when the two solutions become of equal
concentration.
(f) Diffusion pressure gradient (DPG) : The rate of diffusion is directly proportional to the difference of
diffusion pressure at the two ends of a system and inversely proportional to the distance between the two.
(iv) Significance of diffusion
Gaseous exchange during the processes of photosynthesis and respiration takes place with the help of
diffusion.
The process of diffusion is involved in the transpiration of water vapours.
Aroma of flowers is due to diffusion of volatile aromatic compounds to attract pollinating animals.
During passive salt uptake, the ions are absorbed by process of diffusion.
Diffusion helps in translocation of food materials.
Gaseous exchange in submerged hydrophytes is takes place by general surface of the cells through
diffusion.
(3) Permeability : Permeability is the degree of diffusion of gases, liquids and dissolved substances through a
membrane. Different types of membranes may be differentially permeable to different substances. Normally,
permeability of a given membrane remains unchanged, but it may change with alteration in the environmental
conditions of the cell.
(i) Types of membranes on the basis of permeability
(a) Permeable membrane : These membranes allow free passage of solvent (water) and most of the
dissolved substances. e.g., cell wall in plant cells. Filter paper is made up of pure cellulose it also functions as
permeable membrane.
(b) Impermeable membrane : This type of membranes with deposite of waxy substances like cutin and
suberin, do not allow the entry of water, dissolved substances and gases. e.g., suberized walls of cork cells, cuticle
layer of leaf.
(c) Semi-permeable membrane : These membranes permit the movement of solvent molecules only
through them, but prevent the movement of solute particles. e.g., egg membrane, animal plasma membrane,
parchment membrane, copper ferrocyanide membrane, membranes of collodion.
(d) Selectively or Differentially permeable membrane : This type of membranes allow selective passage
of solutes along with solvent, through them. e.g., Osmotic diffusion of water through selectively permeable
membrane start from higher water potential to lower water potential. Many biological membranes such as cell
Chapter 17 245
Transport in Plants
membrane (plasmalemma), tonoplast (vacuolar membrane) and the membranes surrounding the sub-cellular
organelles are selectively permeable. A non-living selectively permeable membranes is cellophane.
(ii) Theories of cell permeability : Following theories are given for cell permeability :
(a) Sieve theory : Rhouhland and Hoffman described that, small pores are found on membranes.
The molecules which are small in size than pores of membrane are only passed through these
membranes.
So the molecules of glucose diffused faster as comparatively sucrose (bigger size) molecules.
(b) Solubility theory : According to Overtone, formation of membranes take place by fats. Therefore
membranes are permeable for those molecules, which are dissolve easily in it.
On the basis of this theory, the permeability of fat insoluble substances like sugar, minerals and amino acids
cannot explained.
(c) Electro capillary theory : Michaelis, Scorth and Loyad proposed modified theory of sieve theory.
According to this theory pores found on membranes are surrounded by charged proteins.
Permeability depends upon the size of charged particles present on pores, size of pore and the charge
present on pores.
So if ionizing substance are smaller than pores, it can pass through membrane.
In the same way both positive and negative ions pass through the uncharged pores. But positive ions
moves through negatively charged pores and negative ions moves through positively charged pores.
(d) Carrier concept : According to this concept, movement of substances through membrane required two
types of carriers called carrier particle and carrier vesicles.
Carrier particles : These type of particles attached with solutes and forms carrier solute complex. Because it
shows chemical affinity to solutes.
After reaching on inner surface of membrane this carrier, solute complex breakdown.
Solute enters into the cell and carrier transferred to outer surface.
Carrier vesicles : Wheeler and Hanchey (1971) described that the transportation of substances in higher
plants take place by the means of pinosomes.
Pinosomes originate by infoldings of cells. It shows bulk transportation.
(4) Osmosis : Osmosis (Gr. Osmos = a pushing or impulse) was discovered by Abbe Nollet in 1748 and also
coined the term 'osmosis'. First of all Traube (1867) use copper ferrocyanide and develop semipermeable
membrane to show its utility in the osmosis of plant physiology. First time Pfeffer in (1887) develop osmoscope by
using semipermeable membrane.
Osmosis is special type of diffusion of a liquid, when solvent moves through a semipermeable membrane from
a place of higher diffusion pressure to a place of lower diffusion pressure.
Chapter 17 246
Transport in Plants
Or
It is the migration of solvent from a hypotonic solution (of lower concentration) to hypertonic solution (of
higher concentration) through a semi-permeable membrane to keep the concentration equal.
In osmosis, the water (or solvent) molecules moves as follows :
From the region of To the region of
Pure solvent (water) Solution
Dilute solution Concentrated solution
High free energy of water molecules Low free energy of water molecules
Higher chemical potential (or water potential) Lower chemical potential (or water potential)
Higher diffusion pressure of water Lower diffusion pressure of water
In formalin preserved Spirogyra filament, selective permeability of plasmamembrane is lost and hence no
effect on placing in hypertonic solution.
If salt presents in higher concentration in a cell than outer side, water will enter in the cell by osmosis.
(iv) Differences between diffusion and osmosis
S.No. Diffusion Osmosis
(1) It is the movement of particles, molecules or It is the movement of solvent of water from the area of its
ions from the region of their higher free energy higher free energy or chemical potential to the area of its
to the region of their lower free energy. lower free energy or chemical potential through a semi-
permeable membrane.
(2) It can occur in any type of medium. It occurs only in liquid medium.
(3) The diffusing molecules may be solids, liquids It involves the movement of solvent molecule only.
or gases.
(4) It does not require a semi-permeable A semi-permeable membrane is required for the operation
membrane. of osmosis.
(5) It is purely dependent upon the free energy of It depends upon the free energy chemical potential of the
the diffusing substance only. solvent present on the two sides of the semi-permeable
membrane.
(6) An equilibrium in the free energy of diffusing An equilibrium in the free energy of solvent molecule is
molecules is achieved in the end. never achieved.
(v) Osmotic pressure (OP) : Pfeffer coined the term osmotic pressure.
Osmotic pressure of a solution is the pressure which must be applied to it in order to prevent the passage of
solvent due to osmosis.
Chapter 17 247
Transport in Plants
Or
Osmotic pressure is that equivalent of maximum hydrostatic pressure which is produced in the solution, when
this solution is separated from its pure solvent by a semipermeable membrane.
It can also be defined as "the excessive hydrostatic pressure which must be applied to it in order to make its
water potential equal to that of pure water". Osmotic pressure is equal to the pressure which is needed to prevent
the passage of pure water into an aqueous solution through a semi-permeable membrane. In other words, it is that
pressure which is needed to check the process of osmosis.
(i) Types of osmosis : Depending upon the movement of water into or outward of the cell, osmosis is of two types.
(a) Endosmosis : The osmotic inflow of water into a cell, when it is placed in a solution, whose solute
concentration is less than the cell sap, is called endosmosis e.g., swelling of raisins, when they are placed in water.
• When a fish of marine water kept in fresh water than it will be die due to endosmosis.
• An animal cell placed pure water will swell up and brust.
• Pollen grains of some of plants germinate on stigma soon but they burst in water or dilute sugar solution.
(b) Exosmosis : The osmotic outflow of water from a cell, when it is placed in a solution, whose solute
concentration is more than the cell sap, is called exosmosis. e.g., shrinkage of grapes, when they are placed in
strong sugar solution.
(ii) Demonstration of osmosis
(a) Thistle funnel experiment to show osmosis : Tie the mouth of a thistle funnel with an egg membrane
or animal bladder which are semi-permeable in nature. Put sugar solution (hypertonic solution) inside the thistle
funnel. Thistle funnel is dipped in water with the help of a stand. A rise in level is noticed after some time. This is
due to the diffusion of water into thistle funnel through semi-permeable membrane by the process of osmosis.
(b) Demonstration of osmosis by potato osmoscope : Peel of the skin of large sized potato with the help
of scalpel. Cut its one end to make the base flat. Make a hallow cavity in the potato almost up to the bottom. Put
sugar solution into the cavity and mark the level by inserting a pin in the wall of the cavity of tuber. Place the potato
in beaker containing water. After some time, it will be noticed that level in cavity rise. It is due to phenomenon of
osmosis. The experiment demonstrates that living cells of potato act as differentially permeable membrane.
Pin Pins
Potato
Petri-dish
Water
Sugar
Solution
Peeled lateral
side of potato
(A) (B)
Osmosis cannot be demonstrated by a potato osmoscope using a solution of NaCl instead of sugar because
the potato tissue is permeable to salt solution.
(iii) Osmotic concentrations (Types of solutions) : A solution can be termed as hypotonic, hypertonic
and isotonic depending upon its osmotic concentration, with respect to another solution or cell sap.
Chapter 17 248
Transport in Plants
(a) Hypotonic solution (hypo = less than). A solution, whose osmotic concentration (solute potential) is less
than that of another solution or cell sap is called hypotonic solution. If a cell is placed in such a solution, water start
moving into the cell by the process of endosmosis, and cell become turgid.
(b) Hypertonic solution (hper = more than). A solution, whose osmotic concentration (solute potential) is
more than that of another solution or cell sap is called hypertonic solution. If a cell is placed in such a solution,
water comes out of the cell by the process of exosmosis and cell become flaccid. If potato tuber is placed in
concentrated salt solution it would become shrink due to loss of water from its cell.
(c) Isotonic solution (iso = the same). A solution, whose osmotic concentration (solute potential) is equal to
that of another solution or cell sap, is called isotonic solution. If a cell is placed in isotonic solution, there is no net
changes of water between the cell and the solution and the shape of cell remain unchanged. The normal saline
(0.85% solution of NaCl) and 0.4 m to 0.5 m solution of sucrose are isotonic to the cell sap.
Osmotic concentration of a solution may governed by concentration of solute, temperature of solution,
ionization of solutes and hydration of the solute molecules.
In xerophytes, the osmotic concentration of cell sap is more than normal. e.g., A molar solution of sucrose
separated from pure water by such a membrane has an OP of approximately 22.4 atmospheres at 0°C. The osmotic
pressure of given solution can be calculated by using the following relationship.
Osmotic pressure = CST
Where, C = Molar concentration of solution, S = Solution constant, which is 0.082 and T = Absolute
temperature i.e., 273°C.
Sucrose is non-ionizing substance while NaCl is ionizing substance. Osmotic pressure of a solution of ionizing
substance is greater than that of equimolar concentration of non-ionizing substance. e.g., 0.1M sucrose solution has
an OP of 2.3 bars while 0.1M sodium chloride solution has value of 4.5 bars.
(vi) Significance of osmosis in plants
(a) The phenomenon of osmosis is important in the absorption of water by plants.
(b) Cell to cell movement of water occurs throughout the plant body due to osmosis.
(c) The rigidity of plant organs (i.e., shape and form of organism) is maintained through osmosis.
(d) Leaves become turgid and expand due to their OP.
(e) Growing points of root remain turgid because of osmosis and are thus, able to penetrate the soil particles.
(f) The resistance of plants to drought and frost is brought about by osmotic pressure of their cells.
(g) Movement of plants and plant parts, for example, movement of leaflets of Indian telegraph plant, bursting
of many fruits and sporangia, etc. occur due to osmosis.
(h) Opening and closing of stomata is affected by osmosis.
(5) Osmotic relation of cell : In a plant cell, however, two membranes are present between the cell sap and
the surroundings the cell-wall is a permeable membrane that does not interfere with the movement of water and
solutes into or out of the cell. The plasma membrane and vacuolar membrane (tonoplast) with the thin layer of
Chapter 17 249
Transport in Plants
cytoplasm between them behave as differentially permeable membrane. Cell sap of a cell is a mixture of water and
soluble substances. Water absorption in root hair from soil is depends on the concentration of cell sap. So a cell
behave as a osmotic system in which endosmosis generate following pressures –
(i) Turgor pressure (TP) : The plant cell, when placed in pure water, swells but does not burst. Because of
negative osmotic potential of the vacuolar solution (cell Plasma membrane
sap), water will move into the cell and will cause the Cell wall Vacuolar sap
plasmalemma be pressed against the cell wall. The actual
pressure that develops that is the pressure responsible for Osmotic Turgor pressure Wall
pushing the membrane against cell wall is termed turgor pressure pressure
pressure.
In other words, we can say that when water enters Fig : A cell showing turgor pressure, wall pressure and
the living cell, a pressure is developed within the cell due osmotic pressure
to turgidity. The hydrostatic pressure developed inside the cell on the cell wall due to endosmosis is called turgor
pressure. It is responsible for growth of young cells.
Significance of turgidity in plants
It provides stability to a cell.
Turgidity keeps the cell and their organelles (mitochondria, plastids and microbodies) fully distended. This
is essential for plants to live and grow normally.
Turgor pressure helps in cell enlargement, consequently in stretching of the stems and in keeping leaves
erect and fully expanded.
The turgid cells provide mechanical support necessary for the non woody tissues (maize, sugarcane,
banana etc.).
Loss of turgidity leads to wilting of leaves and drooping of shoots.
The opening and closing of stomata are regulated by the turgidity of the guard cells.
Leaf movements (seismonastic movement) of many plants (such as bean, sensitive plant Mimosa pudica)
are controlled by loss and gain of cell turgor.
Due to turgid pressure plumule and radicles force out from seeds at the time of seed germination.
(ii) Wall pressure (WP) : Due to turgor pressure, the protoplast of a plant cell will press the cell wall to the
outside. The cell wall being elastic, presses back the protoplast with a pressure equal in magnitude but opposite in
direction. This pressure is called wall pressure. Wall pressure 20
(WP) may, therefore, be defined as 'the pressure exerted by the Equivalent pressure.CM Osmotic
cell wall over the protoplast to counter the turgor pressure. concentration
Normally wall pressure is equal and opposite to turgor pressure 10 Diffusion pressure deficit Cell fully turgid
(WP =TP) except when the cell become flaccid. The value of Turgor (water-saturated)
the two forces continue to rise with the continued entry of pressure
water, till the cell becomes fully turgid.
1.0 1.2 1.4
Relative volume of cell
Chapter 17 250 Fig : Relationship between diffusion pressure deficit
and other pressure
Transport in Plants
(6) Interrelationship of DPD, OP and TP (WP) : DPD indicates the sucking power of suction pressure. As
water enters into the cell the TP of the cell is increased. Cell wall exerts equal and opposite WP against TP. The
actual force responsible for entry of water will be therefore OP–TP
i.e., DPD = OP – WP (As WP = TP)
DPD = OP – TP
Consider that a plant cell with OP = 10 atm. is immersed in pure water. In the beginning TP inside the cell is
zero i.e.
DPD = OP = 10 atm.
When water enters into the cell, TP increases. Turgidity increases and cell wall develops equal and opposite
WP. At the stage of equilibrium TP = 10 atm. and DPD will become zero. It is important to note that OP was same
when cell was flaccid and turgid.
DPD = OP – TP
= 10 – 0 = 10 (when flaccid)
= 10 – 10 =0 (when turgid)
The entry of water in cell to cell depends up on the DPD and not on OP and TP. This can be examplified as
follows : OP=8 OP=10
TP=4 TP=8
DPD=2
DPD=4 (Lower DPD)
(Higher DPD)
(A) (B)
Fig : Relation between diffusion pressure deficit
and entrance of water in the cell
A cell (A) with OP = 8 and TP = 4 is surrounded by the cells (B) with OP = 10 and TP = 8.
Then for cell A, DPD = OP – TP
=8–4
=4
Similarly for cell B, DPD = OP – TP
= 10 – 8
=2
Since the DPD of cell A is more, it has less water and, therefore water would diffuse from cell B into the cell A
(because that DPD of cell B is less than that of A or it has more water than cell A). The entry of water into the cell A
would stop when DPD of both the cells becomes equal. In this way water moves from a cell with less DPD into the
cell with more DPD. Thus, DPD is the osmotic parameter, which determines the flow of water from one cell to
another.
Under given suitable conditions, the DPD more than OP when TP is negative. DPD of a cell mainly depends
upon OP. If two cells have the same OP but differ in TP, the direction of the movement of water from higher TP to
lower TP.
(7) Plasmolysis (Gr. Plasma = something formed; lysis = loosing) : If a living plant cell is placed in a
highly concentrated solution (i.e. hypertonic solution), water comes out of the cell due to exosmosis, through the
Chapter 17 251
Transport in Plants
plasmamembrane. The loss of water from the cell sap causes shrinkage of the protoplast away from the cell wall in
the form of a round mass in the centre. "The shrinkage of the protoplast of a living cell from its cell wall due to
exosmosis under the influence of a hypertonic solution is called plasmolysis". The stage of plasmolysis, when the
protoplast just begins to contract away from the cell wall is called incipient plasmolysis. The stage when the cell
wall has reached its limit of contraction and the protoplast has detached from cell wall attaining spherical shape is
called evident plasmolysis. In a plasmolysed cell, the space between the contracted protoplast and the cell wall
remains filled with external solution. If a cell with incipient plasmolysis is placed in a hypertonic solution it will show
more plasmolysis.
If a plasmolysed cell is placed in pure water or hypotonic solution, endosmosis takes place. The protoplast
attains its original shape and the cell regains its original size. "The swelling up of a plasmolysed protoplast due to
endosmosis under the influence of a hypotonic solution or water is called deplasmolysis'. Deplasmolysis is possible
only immediately after plasmolysis otherwise the cell protoplast becomes permanently damaged. Leaf of
Tradescantia is used for demonstration of plasmolysis in laboratory. The value of TP becomes zero at the time of
limiting plasmolysis and below zero during incipient and evident plasmolysis.
Elastic force H2O
of cell wall
Chloroplast Turgor
pressure
H2O
Nucleus Vacuole filled Cell placed in strong salt Cell placed in pure water
(A) with cell sap solution
Result : Increased turgor
Result : Plasmolysis pressure
(C)
(B)
Fig : Plasmolysis and deplasmolysis (A) Normal cell (B) Plasmolysed cell
(C) Deplasmolysed cell and increased turgor pressure
Significance of plasmolysis : It proves the permeability of the cell wall and the semipermeable nature of
the protoplasm.
The OP of a cell can be measured by plasmolysis. The OP of a cell is roughly equal to the OP of a
solution that causes incipient plasmolysis in the cell.
Salting of pickles, meat, fishes etc. and addition of sugar to jams, jellies, cut fruits etc., prevent their decay
by microbes, as the latter get killed due to plasmolysis or due to high concentration of salt or sugar.
By salting, the weeds can be killed from tennis courts and the growth of plants can be prevented in the
cracks of walls.
Plasmolysis is helpful in determining whether a particlular cell is living or dead as plasmolysis does not
occur in a dead or non living cell.
(8) Water potential (ψ) : The movement of water in plants cannot be accurately explained in terms of
difference in concentration or in any other linear expression. The best way to express spontaneous movement of
Chapter 17 252
Transport in Plants
water from one region to another is in terms of the difference of free energy of water between two regions. Free
energy is the thermodynamic parameter, that determine the direction in which physical and chemical changes must
occur. The potential energy of water is called water potential. e.g., water is stored behind a dam. When the water
runs downhill, its potential energy can be converted to electrical energy. This conversion of energy of water is due to
gravity. The other source that provides energy to water is pressure. The increasing pressure increases the free
energy there by increasing water potential.
Water running downhill due to gravity can be made to run uphill by overcomming the water potential (energy)
by applying pressure. This means that water moves from the point, where water potential is greater to the other,
where water potential is less. The difference in water potential between two points is a measure of the amount of
work or energy needed to move water from one point to the other. Thus, based on the concept of water potential,
the direction of water movement can be predicted. Water potential is measured in terms of pressure.
Measurement unit of water potential is pascal, Pa (1 mega pascal, Mpa = 10 bars). It is represented by Greek
letter, Psi (ψ). Water potential ψw is the difference between chemical potential of water at any point in a system (µω)
and that of pure water under standard conditions (µω°). The value of water potential can be calculated by formula :
ψw = (µω) – (µω°) = RT 1 n e/e°
where ψw = water potential, R is gas constant, T is absolute temperature (K), e is the vapour pressure of the
solution in the system at temperature T, and e° the vapour pressure of pure water at the same temperature.
The direction in which water will move from one cell to another cell depends on water potential in two regions.
Water potential is measured in bars. A bar is a pressure unit which equals 14.5 lb/in2, 750 mm Hg or 0.987 atm.
Water potential of pure water at normal temperature and pressure is zero. This value is considered to be the
highest. The presence of solute particles reduces the free energy of water and thus decreases the water potential.
Therefore, water potential of a solution is always less than zero or has negative value. External pressure increases
the water potential. If a pressure greater than atmospheric pressure is applied to pure water, the water potential can
be raised from zero to a positive value. The water potential is equal but opposite in sign to the diffusion pressure
deficit (DPD). In terms of DPD, the movement of water takes place from the region of lower DPD to the region of
higher DPD, while in terms of water potential (ψ), the flow of water occurs from the region of higher water potential
(less negative) to the region of lower water potential (more negative). The movement of water continue till the water
potential in two regions becomes equal.
(i) Component of water potential : When a cell is subjected to the movement of water, many factors begin to
operate which ultimately determine the water potential of cell sap. For solutions, such as contents of cells, water
potential is determined by three major sets of internal factors viz., matric potential (ψ m), solute potential (ψ s) and
pressure potential (ψ p). The water potential (ψ) in a plant cell or tissue can be written as the sum of the matric
potential (ψ m) due to binding of water to cell walls and cytoplasm, the solute potential (ψ s) due to concentration of
dissolved solutes, which by its effect on the entropy components reduces the water potential and the pressure potential
(ψ p) due to hydrostatic pressure, which by its effect on the energy components increases the water potential :
ψ = ψ m + ψ s + ψ p …… (1)
Each component potential is discussed separately below :
(a) Matric potential (ψ m) : Matric is the term used for the surface (such as, soil particles, cell walls,
protoplasms, etc.) to which water molecules are adsorbed. The matric potential (ψ m) is the component of water
Chapter 17 253
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