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Plant Kingdom Part 3

(a) Microsporophyll : The microsporophylls or 'stamens' are spirally arranged in a compact manner on the
cone axis. The microsporophyll is a brown coloured triangular structure consisting of a short stalk or 'filament' and a
leaf like flattened structure of 'anther'. Each sporophyll is provided with two microsporangia on its abaxial surface.
The terminal sterile portion of the sporophyll is turned upward to protect the upper sporangia. It is called
apophysis. Some of the lower microsporophylls are sterile having no sporangia associated with them.

Micro
sporophyll
Pollen grains

Sterlie portion

Microsporangia Dehisced
microsporangia

Microspores

(A) Micro (A) (B)
sporangium
(B) Fig : Pinus (A) Ventral view of microsporophyll
(B) Ventral view of microsporophyll with dehisced
Fig : (A) A young male cone of Pinus
(B) Male cone in radial longitudinal section microsporangia

(b) Microsporangium : The microsporangia are sessile elongated, cylindrical, structures. The sporangial
development is of eusporangiate type. Each sporangium consists of a 2–3 layered wall. The inner most wall layer
is called tapetum, which encloses a mass of sporogenous tissue. The sporogenous cells divide and re-divide and
finally behave as microspore mother cells or pollen mother cells (PMS). The PMS undergo meiosis to form
tetrahedral tetrads of microspores. The tapetum is a nutritive layer which degenerates at maturity of the anther.

(ii) Female cone : The female cone is an elongated, ovoid structure comprising a central cone axis on which
the ovuliferous scales and bracts are spirally arranged in acropetal order. Usually the cone is 15 – 20 cms. long but
in P. lambertiana they are 60 cms. long. The female cones take three years time to develop and mature.

The cones are produced in clusters of 1 to 4 from places where normally dwarf or spur shoots have developed.
They arise in a group of 1 – 4 cones on a long shoot in the axil of a scale leaf in place of a dwarf shoot. In the first
year, the female cone is reddish-green measuring about 1–2 cms in length having compactly arranged sporophylls.
The second year cone is much larger, again with compact sporophylls. In the third year, the cone axis elongated
and hence the sporophylls separate from each other.

(a) Megasporophyll : Each megasporophyll is differentiated into two parts – Lower part is bract scale and
upper part is ovuliferous scale.

 Bract scales : These are small, dry, membranous structures attached with the cone axis directly. These
are also known as carpellary or cover scales. At the time of maturity, these bract scales become rolled up
and thus help in the dispersal of seeds.

Chapter 12 155

Plant Kingdom Part 3

 Ovuliferous scale : This is a woody, brownish structure borne on the dorsal side of the bract scale. Each
ovuliferous scale is triangular with narrow basal part and upper broader part in the form of disc, known as
apophysis. The apophysis appears to be rhomboidal and possesses a small point known as umbo. On the
dorsal side, near the base of each ovuliferous scale, are attached two ovules with their micropyles directed
towards the cone axis. Florin gave the term seed scale complex to the bract scale along with associated
ovuliferous scale.

Embryo sac Nucellus
Pollen

chamber

Ovuliferous

scale

Bract scale

Ovule Micropyle

Ovuliferous Megasporophyll

scale Vascular

Bract scale trace

Cone axis

(A) (B)

Fig : Female cone of Fig : Pinus (A) Longitudinal section of
Pinus female cone (B) A megasporophyll

(b) Megasporangium : Each ovule is an oval and anatropous structure consisting of a central mass of
parenchymatous tissue, the nucellus, surrounded by a two lipped protective covering the integument which is united
with nucellus except at the micropylar end where it prolongs to form a short tube beyond the nucellus. A small
space is left in the upper region of nucellus below the integument, which is known as pollen chamber. Integument is
differentiated into 3 layers although differentiation is not so distinct as in Cycas.

Outer fleshy layer : Made up of thin walled cells which disappears at Micropyle

maturity. Pollen chamber
Pollen tube

Middle stony layer : Very conspicious. Outer fleshy
Inner fleshy layer : Inner fleshy layer is well developed. layer

Nucellus
Inner fleshy layer

At the apex of the nucellus, a hypodermal cell gets enlarged and Archegonium

differentiated, it is called archesporial cell. The archesporial cell divides Female
periclinally into an upper tapetal cell which forms tapetum, the nourishing gametophyte
layer, and the lower megaspore mother cell. This megaspore mother cell
Middle stony
layer

(sporogenous cell) divides reductionally to form a linear tetrad Fig : Pinus : L.S. of ovule showing
of haploid megaspores. Out of the four megaspores, three lying
towards the micropyle degenerate. The chalazal one matures Exointine Exine archegonia aSntdalkpocelllel n tubes
Intine

into a functional megaspore. Saccus Body
(A) cell
(iii) The gametophyte : The sporogenesis results in the (B) Pollen
formation of micro and megaspores representing the first Prothallial cells Generative cells tube

Tube
cell

Chapter 12 156 (C) (D)
(E)

Fig : Pinus : (A)-(E) Various stages of
microgametogenesis

Plant Kingdom Part 3

gametophyte cells. They undergo gametogenesis so as to form the male and female gametophytes respectively.

(a) Male gametophyte : The unicelled microspore undergoes three divisions of mircogametogenesis, so as to
form a four-celled pollen grain or microgametophyte or male gametophyte. There are two prothallial cells, a
generative cell and a tube cell. The pollen grains, at maturity are protected by three wall layers. The outermost wall
layer, called exine or cappa is cutinised. the second wall layer is called exointine or capulla. It forms two balloon like
outgrowths, on either side, called wings or saccus. The third wall layer is thin and called intine or tenuitas. A
maturity the microsporangia dehisce by a longitudinal slit and the pollen grains are dispersed at 4 – celled stage.
Since, a large number of grains are set free from a cluster of male cones in the form of pale-yellow cloud the
phenomenon is often described as shower of sulphur or shower of golden dust.

(b) Female gametophyte : The functional megaspore enlarges. A vacuole develops in the centre and then its
nucleus divides freely to form about 2000 nuclei. Initially, multinucleate tube like cells are formed called alveoli.
Later, wall formation starts from periphery and proceeds towards the centre. As a result, cellular female
gametophyte or female prothallus or megagametophyte or endosperms is formed. The cells of the nucellus
surrounding the female gametophyte now get modified and form a nutritive layer called endosperm jacket or
spongy layer. The 'endosperm' of Pinus is a haploid gametophytic tissue formed before fertilization.

Archegonium : Near the micropylar end, one to five archegonia are differentiated in the prothallus. Each
archegonium at maturity consists of eight neck cells arranged in two tiers of four each and a venter having a small
ventral canal cell and a large egg. The ventral canal cell disorganizes before fertilization. Neck canal cells are
absent.

(iv) Pollination : The pollination in Pinus is anemophilous. The wings of pollen grains are helpful in

pollination. Just before pollination the female cone axis elongates separating megasporophyll from each other. This

fascilitates pollen grains to reach ovules. There is a long interval of about a year between pollination and

fertilization. Egg
Male gamete
(v) Post pollination changes in the male Egg nucleus
gametophyte : The exine ruptures and the intine protrudes
out to from the pollen tube that grows through the nucellar (A) (B) (C) (D)
tissue. Simultaneously, the generative cell divides to form a Fertilization Oospore 1st nuclear 2nd nuclear

division division

stalk cell and body cell. The body cell then divides to form two (E) (F) Primary
male gametes, which are non-flagellate. 8-celled 12-celled suspensor
proembryo proembryo
(vi) Fertilization : The mode of fertilization was Rosette
discovered by Goroschankin (1883). After reaching the neck (G) Rosette cells
of the archegonium, the tip of the pollen tube ruptures cells
releasing the two male gametes. The ventral canal cell

degenerates and the neck cell split apart. Out of the two, one 16-celled Primary Suspen
male gamete fuses with the egg to form the zygote. The second proembryo suspensors -sors
male gamete along with the stalk and body nuclei degenerates.
Upper tier Secondary
Rostate tier (H) suspensors
Suspensor cells (I) Embryos
elongating

Embryonal tier

Embryo(k)

Chapter 12 157 (J)

Fig : Pinus : Embryogeny

Plant Kingdom Part 3

(vii) Embryogeny : The proembryonal development in Pinus was studied by Buchholz (1918). The zygotic
nucleus moves toward the base and then divides to form four nuclei. These nuclei organise into four quadrately
arranged (diagonally opposite) cells with open upper end. The four cells divide simultaneousing thrice to form four
tiers of four cells each. These tiers are designated from top downwards as open tier, rosette tier, suspensor tier and
apical tier. Since only a part of the oospore is involved in the formation of the embryo, the development is said to
be meroblastic.

As there is no cell wall on the micropylar end, the cells of open tier provide nutrition to the remain tiers of the
proembryo. The cells of this tier do not divide. The cells of rosette tier divide in various planes. They simply conduct
the food obtained by the cells of open tier. The cells of suspensor tier elongate pushing the embryonal cells into the
'endosperm'. The four suspensor cells due to considerable elongation may become coiled. These cells may divide
transversely to form secondary suspensor or embryonal tubes. By another transverse division, two whorls of
embryonal tubes, designated as first and second series of embryonal tubes, are formed. All the four cells of
embryonal tier separate from one another and develop into four independent embryos. The formation of more than
one embryos from one oospore is called cleavage polyembryony. Another type of polyembryony found in Pinus is
simple polyembryony i.e. when more than one embroys are developed as a result of fertilization of different
archegonia. Thus in Pinus although both types of polyembryony are found but at maturity seed contains only one
embryo as food is not sufficient for survival of many embryos. The embryo soon gets differentiated into radicle,
plumule, hypocotyl and cotyledons. The number of cotyledons is always more than two (Schizocotyly).

(viii) Seed formation : Seed of Pinus is winged. The wing develops from the upper surface of ovuliferous
scale. Seed has thin withered outer coat, which is pieled off, a stony coat, papery coat, cap like perisperm and food
laden endosperm which encloses a central embryo. Embryo possesses 9–14 cotyledons (P.roxburghii). A seed
represents three generations – parents sporophyte (tesla, tegmen and perisperm, if present), new sporophyte
(embryo) and female gametophyte or endosperm.

(ix) Seed germination : The seeds may remain dormant for several years. The germination of seed occurs
when the environmental conditions are favourable. The radicle protrudes out through the micropyle and enters the

Seedling Pinus tree Male cone

Embryo in seed Sporophytic Female cone Microsporophyll
Oospore generation Ovuliferous scale

Diplophase (2n)

Megasporangium or Microsporangium
nucellus

Fertilization Endosperm Gametophytic Megaspore mother Microspore mother
Oosphere Archegonium generation cell cell
Haplophase (n)
Male gamete Melosis
Female prothallus
or endosperm Megaspore

Antheridial cell Male prothallus Microspore

Fig : Graphical representation of life cycle of Pinus

Chapter 12 158

Plant Kingdom Part 3

soil forming the primary root. The plumule comes out and along with cotyledons it is pushed in air due to
elongation of hypocotyl. The germination is, therefore, epigeal. The plumule forms a few juvenile leaves or
prophylls. The juvenile leaves are spirally arranged on the branch of unlimited growth. Long shoots arise in their
axis. Later on, they dry up as scales. The rate of growth of Pinus is quite slow.

(4) Economic importance :

(i) Seeds of some species are edible e.g., P. gerardiana (chilgoza), P. edulis.

(ii) Fossilized resin (amber) is obtained from P. succinifera and is of great commercial value.

(iii) Some species of Pinus are cheap source of cellulose.

(iv) Some species are used for manufacture of paper.

(v) Wood gas, wood tar and wood alcohol are obtained from Pinus.

(vi) Wood of Pinus is used for making furniture, electric poles, doors, windows, match sticks e.g., P. longifolia
(chir) and P. excelsa (kail)

Cycas.

Systematic position

Kingdom – Plantae

Sub kingdom – Embryophyta

Phylum – Tracheophyta

Class – Gymnospermae

Order – Cycadales

Family – Cycadaceae

Genus – Cycas (For UP CPMT Students Only)

(1) Habitat : Cycas is an evergreen palm-like plant. It is the only genus of family Cycadaceae represented in
India. Cycas has approximately 20 species found in Australia, New Zealand, Japan, China, India, Burma
(Myanmar) and Pacific Islands.

In India, four Cycas species are common in Orissa, Bengal, Assam, Tamilnadu, Karnataka and Andaman.

(i) Cycas revoluta : It is a native of China and Japan and is locally called Tesso. In our country, it is called
'Sagopalm'. Due to its primitive characters, it is also called living fossil. It is upto 10 ft tall.

(ii) Cycas circinalis : Plants are about 12 to 15 ft tall and distributed upto 3500 ft. In Hindi, it is called as
Janglimadan mast-ka-phul.

(iii) Cycas rumphii : Plants are about 12 ft tall. It is also cultivated in Indian gardens. In Tamil, it is called
Kama, Paiyindu.

(iv) Cycas beddomei.

(2) Structure

Chapter 12 159

Plant Kingdom Part 3

(i) External structure : Fully grown plants attain a height of 2– 5 m although C. media attains a height of
20m. The main plant body is differentiated into root, stems and leaves.

(a) Roots : Roots arise from lower part of stem and are of two
types :

 Normal roots : These form a primary tap root system. These

roots are not green, positively geotropic with no root hairs. Scale leaves
 Coralloid roots : From the lateral branches of the normal

roots are formed dichotomously branched, apogeotropic,

bluish green coralloid roots. Anabaena cycadacearum, Nostoc

and bacteria are found in their cortex and sometimes enter in Megasporophylls

these roots also. It is an example of symbiosis. It helps in Armour of woody Foliage leaves
fixation and absorption of nitrogen. leaf bases Bulbil
Steam

(b) Stem : Stem is thick, cylindrical, columnar, small, aerial and Fig : External morphology of Cycas

unbranched. It is covered with persistant leaf bases and scale leaves, which are found in alternate whorls. There is a

crown of foliage leaves at the apex of the plant.

(c) Leaves : Cycas has two types of leaves (dimorphism).

 Scale leaves : These are reduced form of foliage leaves without lamella and are arranged in a compact
spiral and alternate manner around the apex and no reproductive structures. These are protective in
nature. A single scale leaf is a brown, dry, woody, triangular structure, covered with brown hairs or
ramenta.

 Foliage leaves : These are green unpinnately compound present on the apex of the plant forming a
crown. These leaves are upto 3 metres in C. circinalis. Leaves are leathery and thick, some leaflets at the
base of the rachis are reduced to spines. These are mainly photosynthetic in nature.

Leaves in Cycas show xerophytic characters.

(ii) Internal structure

(a) Root

 Normal root : The structures of normal root resembles dicotyledonous root. T.S. of normal root reveals
the following structures

Epiblema : This is the outermost layer with unicelled root hairs.

Cortex : Just below the epiblema is multilayered parenchymatous cortex. Some tannin cells are present in the
cortex.

Endodermis : Below the cortex is present endodermis which is made up of barrel-shaped cells and below it is
a layer of pericycle.

Vascular tissues : It consists of xylem and phloem which are radially arranged, i.e., on different radii.

Chapter 12 160

Plant Kingdom Part 3

Pith : It is generally absent.
Secondary growth : It is like dicotledonous plants.
 Coralloid root : Structure of stele is similar to normal roots but cortex is divided into three zones :
Outer cortex : Having several layers of parenchymatous cells.
Middle cortex (Algal zone) : Filled with blue green algae, Anabaena and Nostoc.
Inner cortex : Having several layers of parenchymatous cells. Roots are diarch, triarch and sometimes
polyarch.

Tanin cell Phellem or
Cork
Root hair
Epiblema Phellogen
Parenchyma
Tanin cell Outer cortex

Endodermis Middle cortex
Pericycle (algal zone)
Phloem Inner cortex
Metaxylem Endodermis
Protoxylem Pericycle
Phloem
Metaxylem
Protoxylem

Fig : T.S. normal root of Cycas Fig : T.S. coralloid root of Cycas

(b) Stem : It resembles a dicotyledonous stem having the following tissues :

Epidermis : It is the outermost incomplete layer ruptured due to persistent leaf bases. It is made up of
compactly arranged thick-walled cells.

Cortex : Cortex is large, thin-walled, parenchymatous, having a number of mucilage canals. Starch grains are
found in the cortex.

Endodermis and pericycle : These layers are not very clear.

Stele : Vascular cylinder is very small having numerous small closely arranged vascular bundles, which are
conjoint, collateral and open. Xylem is endarch and consists of tracheids, which have spiral thickening in
protoxylem and scalariform thickenings in metaxylem. Phloem is devoid of companion cells. Albuminous cells are
found in phloem.

Leaf traces : There are several leaf traces present in the cortex. Four vascular bundles enter the base of leaf,
two of these are direct and other two arise from the stele of opposite side and after making semicircle, they enter the
leaf. These indirect leaf traces are known as girdling leaf traces of leaf girdles.

Pith : It is large, parenchymatous and is having a number of mucilage canals. Starch grains are also found in
pith.

Chapter 12 161

Plant Kingdom Part 3

 Secondary growth : The secondary growth in initiated by the formation of a cambium ring due to the
development of interfascicular cambial strips and their subsequent joining with the intrafascicular cambia.
This ring cuts secondary xylem on the inner side and secondary phloem on the outer side in additions to
secondary medullary rays on both sides. This cambium ring now ceases to function another cambium now
arises pericycle or inner layers of cortex. The new cambium functions in the normal way like the old one.
Thus, concentric rings of secondary xylem and secondary phloem are formed. Such a wood is called as
polyxylic i.e., comprising more than one xylem cylinders. Due to the presence of alternating rings of thin
walled tissue (phloem) the wood of xylem remains loose and hence it is described as manoxylic. The
growth in the extrastelar region takes place by the formation of a phellogen (cork cambium) which cuts off
phellum (cork) on the outer side and phelloderm (secondary cortex) on the inner side. The three layers
jointly constitute the periderm. The secondary growth pattern of Cycas resembles some dicots showing
abnormal secondary growth. Secondary wood is devoid of vessels.

Periderm Rings of Cuticle
secondary xylem Epidermis
Girdling leaf Cortex
Armour of trace Sec. phloem
leaf bases 2nd ring
Leaf trace Pith Sec. xylem
Phloem
Stele 2nd ring
Pith (A) (B)
Indirect trace Medullary ray
Direct trace
Sec. phloem
1st ring

Sec. xylem
1st ring

Medullary ray

Pith

(C)

Fig : Cycas, T.S. of stem (A) Outline diagram of a young stem (B) Old stem showing polyxylic
condition (C) A portion of stem showing two growth rings

The secondary xylem is made up of tracheids showing multiseriate bordered pits. Gregus (1958) however,
reported the presence of vessels in C. revoluta. Bars of sanio have been observed by Sifton, 1915 in the tracheids of
C. revoluta. The secondary phloem comprises sieve cells and fibers. de Bary, 1884, Miller, 1919 reported the
presence of sieve tubes in the secondary phloem but this needs confirmation.

(c) Leaf

 Rachis : In cross section of the rachis is almost circular with two depressions on upper lateral sides where
the leaflets are attached.

Epidermis : The outermost layer is epidermis with thick cuticle Epidermis Chlorenchyma
having stomata. Cuticle

Hypodermis : Epidermis is followed by a well developed Sclerenchyma
hypodermis, differentiated into outer chlorenchymatous and inner
sclerenchymatous regions. Leaflet

Ground tissue : Below the hypodermis is well developed Vascular
parenchymatous ground tissue with mucilage canals. The vascular bundle

Mucillage
canals

Chapter 12 162 Ground
tissue

Fig : T.S. rachis of Cycas

Plant Kingdom Part 3

bundles are arranged forming in inverted omega (Ω). Each vascular bundle is surrounded by a sclerenchymatous
sheath and is conjoint, collateral and open. In most parts of the rachis, xylem is mesarch, i.e., centripetal xylem
towards periphery and two patches of centrifugal xylem one on each side of protoxylem of centripetal xylem outside
the centrifugal xylem is cambium and then phloem towards periphery.

 Leaflet

Epidermis : Epidermis is single layered with thick cuticle. The upper epidermis is complete whereas the lower
epidermis is interrupted by several stomata present only in the region of blade (hypostomatic). Upper and lower
epidermis are covered by layer of thick cuticle.

Hypodermis : Just below the upper epidermis, there are several layers of sclerenchymatous hypodermis
while above the lower epidermis it is present only in the midrib portion.

Mesophyll : Mesophyll is differentiated into palisade parenchyma on upper side and spongy
parenchyma on lower side. Palisade tissue is made up of vertically elongated cells without intercellular spaces.
Both tissues contain chloroplasts.

Vascular bundle : In the midrib there is a large vascular bundle. The vascular bundle is collateral and
closed. The xylem is mesarch, i.e. diploxylic condition with centripetal and centrifugal xylem.

Transfusion tissue : On each side of the midrib in between the palisade and spongy tissues is present

transfusion tissue made up of horizontally arranged tracheids which supply water and mineral to mesophyll tissue

upto margins. Cuticle
Upper epidermis
Centripetal xylem
Hypodermis
Palisade parenchyma

Lamina Spongy parenchyma Sunken stoma
Centrifugal xylem
Midrib
Fig : T.S. leaflet of Cycas (diagrammatic) Phloem Bundle
HyposhdeearmthisTransfusion tissue
Lower epidermis

Fig : T.S. leaflet of Cycas (a portion enlarged)

(3) Reproduction : Cycas plants are dioecious and reproduce by following methods :

(i) Vegetative propagation : It occurs by means of bulbils (resting adventitious buds) which are produced
on the stem in the axil of scale leaves. They break up from the parent plant and germinate to give rise to new plant.

(ii) Sexual reproduction : Plant of Cycas is sporophyte (2n) and dioecious. The sexual reproduction is of
oogamous type, i.e., takes place by the fusion of distinct male and female gametes. The male and female gametes are
formed by the germination of micro and megaspores which are born on microsporophylls and megasporophylls. the
microsporophylls are grouped together to form a compact conical structure called male cone, whereas the megasporophylls
are not aggregated to form a cone, they are produced at the apex of the stem in succession with the leaves.

Male cone : The male cones are borne every year singly at the apex of the male plant. The growth of the
male plant is, therefore, checked. Later on, a lateral bud develops which pushes the male cone to one side and

Chapter 12 163

Plant Kingdom Part 3

occupies a terminal position. The process is repeated during the formation of subsequent male cones. As such, the
growth pattern of male plant is sympodial.

The male cone is a shortly stalked, oval or elliptical structure measuring about 40 – 60 cms in length. It may
sometimes attain a length of 75 cms. in C. circinalis. Each cone consists of a central axis bearing numerous
microsporophylls arranged in spiral manner.

(a) Microsporophylls : They are wedge - shaped structures with a slightly broad base. They are soft and
fleshy in the younger stages. At maturity, they are hard and woody. They measure about 3 – 4 cms. in length and
1.2 – 2.3 cms. in breadth. They bear sori of sporangia on the abaxial (lower) surface. The terminal sterile portion of
the sporophyll is called apophysis. In the apophyseal region the sporophyll gradually tapers and points upward.

Cone axis

Microsporophylls

Apophysis

Central papilla

Sori Hairs Line of

dehiscence

Microsporangia Microsporophyll

Bracts

(A) (B) Fig : Cycas : (a) Dorsal view of microsporophyll
(b) Ventral view of microsporophyll
Fig : Cycas : (A) External view of male cone
(B) L.S. of male cone (c) Microsporangia in sori (undehisced)

 Microsporangium : The microsporangia are borne in sori on the abaxial surface of the sporophyll. Each

sorus contains 2 – 6 microsporangia. The number of microsporangia may be upto 700 in C.circinalis,

1000 in C. revoluta and 1150 C.media. In between the sporangia are present uni or bicelled epidermal

hair. The microsporangia are short-stalked, oval or elliplical structures. The development of the

sporangium is of eusporangiate type. Each sporangium consists of a 5 – 6 layered wall. The outer most

wall layer is called as exothecium whereas the innermost layer is the tapetum. The tapetum encloses the

sporogenous tissue. The sporogenous cells divide and re-divide to form the microspore mother cells or

pollen mother cells (PMC). The PMC undergo meiosis to form tetrahedral tetrads of spores. The cells of

exothecium develop a thickening along their radial and inner tangential walls. The cells of tapetum and

inner wall layers degenerate at maturity to provide nutrition to the developing pollen grains. The wall of a

mature sporangium, thus comprises exothecium only.

(b) Megasporophyll : The megasporophylls are spirally borne in acropetal Ovule
order on the female plant. Since they are loosely arranged, there is no female cone
formation. Each megasporophyll is regarded as a modified foliage leaf and is Ovule
about 5 – 10 inches long. In the female plant therefore, the apical meristem remains
unaffected. Hence, the growth pattern in the female plant is monopodial. (A) (B) (C)

The megasporophylls is are flat, dorsiventral structures distinguishable into a Fig : (A)-(C) Megasporophylls of
proximal stalk or rachis part and a distal lamina. The margin of lamina is serrate or different species of Cycas
dentate in C. circinalis, C. beddomei and C. rumphii. In the upper part of the rachis
are present 1 – 6 pairs of ovules, laterally. This number is variable in different species
e.g., 1 – 6 pairs in C. revoluta, C. circinalis and only one pair in C. normanbyana.

Chapter 12 164

Plant Kingdom Part 3

 Megasporangium (Ovule) : The ovules of Cycas are largest in nature, can be seen by naked eyes. In
C. circinalis, the ovules are largest in size, i.e., about 6 cm in length and 4 cm in diameter.

The ovules are orthotropous and unitegmic. The main body of the ovule is nucellus, covered by a single
thick integument except at the top where a small opening is left called micropyle.

The integument is distinguishable into three layers, an Micropyle
outer fleshy layer (sarcotesta), middle stony layer (sclerotesta)
and inner fleshy layer (sarcotesta). The outer and inner fleshy Outer sarcotesta
layers are vascularised as also the nucellus by separate bundles. Middle sclerotesta Integument
The apex of the nucellus develops a beak-like process, the
nucellar beak, which projects into the micropyle. Inner sarcotesta

Somewhere in the deep layers of nucellus a megaspore Pollen chamber
mother cell in differentiated. It has a prominent nucleus and
dense cytoplasm. It undergoes meiosis to form a linear tetrad of Archegonia
megaspores. Of these, three micropyler megaspores degenerate
and the lowest functions. The functional megaspore has a thick Nucellus
papillate outer wall called exospore and a thin, fibriller inner
wall, the endospore. Female gametophyte
or Prothallus or
Endosperm

Vascular strands

Fig : L.S. megasporangium (ovule) of Cycas

(c) The gametophyte : As a result of sporogenesis, the micro and megaspores are formed. They are the first
gametophytic cells. The microspores give rise to the male gametophyte whereas the megaspores form the female
gametophyte. The gametophytes reproduce sexually.

 Male gametophyte : The unicelled microspore undergoes two divisions of microgametogenesis and as a
result three cells are formed. These three cells are serially designated as tube cell, generative cell and
prothallial cell. At this stage the pollen grain is double layered. The outer wall exine is much thicker than
intine. The microsporangium dehisces by a longitudinal slit and pollen grains are dispersed at 3-celled
stage.

 Female gametophyte : The nucleus of the functional megaspore divides freely to form a free-nuclear
gametophyte. A vacuole appears in the centre. Wall formation now begins from periphery and gradually
proceeds towards the centre. As a result, cellular female prothallus or megagametophyte or endosperm is
formed. The 'endosperm' in Cycas is a haploid gametophytic tissue formed before fertilization. This is
nutritive in function. Simultaneously, a tiny space develops on the upperside of the ovule between
nuclellus and the female gametophyte due to degeneration of certain nucellar cells. This is called as
archegonial chamber.

Archegonium : The archegonia are formed from the gametophytic cells lining the archegonial chamber. The
number of archegonia formed in a gametophyte is variable e.g., 2 – 8 in C. revoluta, 3 – 6 in C.rumphii and 3 – 8
in C. circinalis. An archegonium consists of a two celled neck but there is no neck canal cell. There is no venter
either. The egg and the ventral canal nucleus remain surrounded by the cells of prothallus. Cycas produces largest
egg in the plant kingdom measuring 0.5 mm. in diameter.

(d) Pollination : The pollination is anemophilous. The pollen grains of Cycas are light in weight and easily
blown away by wind at 3-celled stage (prothallial cell, generative cell, tube cell). At the time of pollination, a large
pollination drop comes out of micropylar end of ovule by disorganisation of nucellar beak. The pollen grains are
entangled on this drop and as it dries, the pollens are drawn into the pollination chamber.

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(e) Post pollination changes in the male gametophyte : After a definite period of rest, the pollen grain
germinates. The generative cell divides into a lower stalk cell and upper body cell. Body cell enlarges and forms
several blepharoplasts, which later forms cilia.

The tube cell elongates, pierces the exine and forms a pollen tube. The pollen tube is slightly swollen and
branched at tip. The pollen tube acts as haustorium absorbing food from nucellus. Body cell divides into two
daughter cells and each daughter cell metamorphoses into one antherozoid or sperm or male gamete.

The male gametes of Cycas are largest (300µ) in nature, visible to naked eye and are oval in form, broad (top-
shaped) and naked at posterior end and spirally coiled in the anterior half with thousands of small cilia. The sperms
pass into pollen tube and reach the tip of the tube.

(f) Fertilization : After reaching the archegonial chamber, the tip of the pollen tube ruptures releasing the
two male gametes. Besides, the tube also discharges a fluid having high concentration. When an antherozoid
touches the neck cells, it is sucked in violently. By the time the ventral canal nucleus has already degenerated. As a
result of syngamy, the zygote is formed. The fertilization in Cycas is, therefore, siphonogamous (by pollen tube)
accompanied by zooidogamy (by flagellate gametes). Thus the fertilization brings to an end of the gametophytic
generation and the zygote is the initial stage of sporophytic generation.

(g) Embryogeny : The zygote, which is the first sporophytic cell, undergoes free-nuclear divisions. A vacuole
develops in the centre pushing the nuclei to the peripheral position. In the upper region there are only a few nuclei
but the lower region contains numerous nuclei. This is followed by wall formation that begins from periphery and
proceeds to centre (centripetal). The cellular proembryo so formed soon gets differentiated into three regions –

Upper : Haustorial region, Middle : Suspensor region and Lower : Embryonal region.

Proembryo forms almost all part of embryo. Suspensor cell elongates and pushes the proembryo down into
the food laden tissue of the gametophyte. Suspensor continue to elongate till they form a exceedingly long, tortuous
and often spirally coiled structure. Proembryo forms, plumule and two cotyledons. Tip of suspensor forms radicle.
As there are several archegonia, several developing embryos may be found in one young seed (polyembryony) but
only one remains at maturity and others perish (potential true polyembryony).

(h) Seed formation : The mature seed of Cycas is an orange-red or reddish-brown structure. The seed is
covered by a thick testa. It is sweet in taste and emits pleasant odour. These two characteristics are responsible for
the their zoochorus, (ornithochorous) dispersal. Major parts of nucellus and inner sarcotesta are used up by the
developing embryo reducing them to thin, papery layers.

The seed of Cycas comprises tissues of three generations namely parent sporophytic (seed coat and nucellus),
gametophytic (endosperm) and second sporophytic (embryo). The embryo is distinguishable into a haustorial tip, a
long suspensor, radicle, hypocotyl, plumule and two cotyledons.

(i) Seed germination : There is hypogeal germination of Cycas seed. In germination, the radicle forms a tap
root. The cotyledons remain in the endosperm under the surface of soil. The plumule grows up and forms some
scale leaves and later foliage leaves. Cycas seed represents 3 generations :

Old sporophytic generation (represented by seed coat and nucellus), Female gametophytic generation
(represented by endosperm), and Future sporophytic generation (represented by embryo).

Life history of Cycas is diplohaplontic. It shows heteromorphic or heterologous type of alternation of generations.

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Germination Cycas plant
sporophyte (2n)

Seed Male plant (2n) Female plant (2n)

Embryo Male cone Megasporophyll
(2n)
Microsporophyll Ovule
Zygote or
oospore Sori Megaspore mother
cell (2n)
(2n) Microsporangium R. D.

Microspore mother Functional Megaspore (n)
cell (2n)
R. D. Female gametophyte
or endosperm
Pollen grains of
spores (n) Archegonium

Male gametophyte

Pollen tube

2 sperms Egg (n)

Fusion

Fig : Graphical representation of life cycle of Cycas

(4) Economic importance
(i) A starch called sago is obtained from the pith of Cycas, that is why Cycas is called sago palm. In Japan
starch extracted from stem of C. revoluta is used for preparing saboodana.
(ii) Seed of some Cycads are used as fodder for animals.
(iii) Leaves are used for making mats and baskets.
(iv) Cycas is an ornamental plants.
(v) Boiled young leaves are eaten as vegetables.
(vi) Extract of young Cycas leaves are used in the treatment of many skin diseases. The decoction of seeds is
used as purgative. Tincture prepared from its seeds is used by Indians in headache, nausea, bad throat, etc.

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(13) Apogamy : The terms apogamy was coined by de Bary (1878). It is defined as formation of sporophyte
from a gametophytic cell other than egg without fertilization. It was first observed by Farlow (1874) in Pteris cretica.
Thereafter it was observed in several other plants e.g., Lycopodium, Selaginella, Nephrodium, Lastrea, Marsilea etc.
The apogamy is of two types, obligate and facultative. If either both of the sex organs are nonfunctional or
absent, the apogamy occurring on account of this is said to be obligate. But if a gametophytic cell is induced to form
the sporophyte without fertilization, the apogamy is called as facultative or induced.

(14) Apospory : The formation of gametophyte from a sporophytic cell without meiosis is called as apospory.
This phenomenon was first observed by Druery (1884) in Athyrium filix-femina. Thereafter it has been established
in several pteridophytes. e.g., Pteridium aquilinum, Asplenium, Trichomanes etc. Induced apospory was seen in
Pteris species.

(15) Parthenogenesis : Formation of sporophyte from egg without fertilization is called as
parthenogenesis. Farmer and Digby (1907) observed that in homosporous, leptosporangiate ferns, apospory was
always followed by parthenogenesis. This phenomenon has been observed in several species of Selaginella and
Marsilea.

(16) Affinities of pteridophytes : The pteridophytes occupy an intermediate place between bryophytes and
spermatophytes. They represent affinities with both the groups.

(i) Similarities with bryophytes

(a) Both have terrestrial mode of life.

(b) Water is indispensable for the process of fertilization.

(c) Male gametes are flagellated.

(d) The structure and ontogeny of sex organs i.e. antheridium and archegonium is based on similar pattern.

(e) Both the groups have definite alternation of sporophytic and gametophytic generations.

(f) Sexual reproduction is of oogamous type. Zygote is retained within the venter of archegonium to form embryo.

(g) Sex organs are surrounded by sterile jacket.

(h) The young sporophyte is partially or wholly dependent on the gametophyte for nourishment.

(ii) Similarities with spermatophytes

(a) In both the cases, sporophytic plant body is large, independently existing and dominant phase of life cycle.

(b) The plant body is differentiated into true stem, leaves and roots.

(c) Vascular tissue is present.

(d) Spores are produced inside the sporangia.

(e) Presence of distinct alternation of generations.

(f) Process of photosynthesis is mainly confined to leaves. Stomata are present on the leaves.

(17) Fossil history of pteridophytes : The pteridophyta have a long fossil history. Their first traces were
identified in the silurian period of paleozoic age (about 400 million years age). Pteridophytes flourished well during
devonian, mississipian and pensylvanian periods of late paleozoic age. This period can be well recognised as "age
of pteridophyta".

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(18) Classification : Eichler (1883) classified the plant kingdom into Cryptogamia and Phanerogamia.
The Cryptogamia was further divided into Thallophyta, Bryophytes and Pteridophyta. Engler (1909) included
Bryophyta and Pteridophyta under Embryophyta. Sinnott (1935) introduced the term Tracheophyta. A years
later Eames (1936) classified Tracheophyta into four groups namely, Psilopsida Lycopsida, Sphenopsida and
Pteropsida, and Pteropsida into Filicinae, Gymnospermae and Angiospermae. Smith (1938) classified pteridophytes
into four classes namely Psilophytineae, Lycopodineae, Equisetineae and Filicineae. Oswald and Tippo (1942)
classified pteridophytes in to four sub-phyla.

(i) Psilopsida
(ii) Lycopsida
(iii) Sphenopsida
(iv) Pteropsida
(19) Salient features of sub-phyla
(i) Sub-phylum : Psilopsida
(a) These are the oldest known vascular plants, most of them (except Psilotum and Tmesipteris) are fossils.
(b) Plant body is relatively less differentiated.
(c) Roots are absent, instead dichotomously branched rhizome is present.
(d) Aerial axis is either naked or have small spirally arranged leaves.
(e) Sporangia are cauline (i.e., directly borne on the axis or stem); they are lateral or terminal in position. e.g.,
Psilotum, Tmesipteris.
(ii) Sub-Phylum : Lycopsida
(a) Plant body is differentiated into root, stem and leaves.
(b) Leaves small (i.e., microphyllous) with a single unbranched vein.
(c) Sporangia develop in the axil of the sporophylls.
(d) Sporophylls generally form compact strobili. e.g., Lycopodium, Selaginella, etc.
(iii) Sub-Phylum : Sphenopsida
(a) Stem differentiated into nodes and internodes.
(b) Leaves microphyllous, present in whorls at each node.
(c) Sporangia are borne on the sporangiophores which form compact cones at the apex of the fertile branches.
e.g., Equisetum.
(iv) Sub-Phylum : Pteropsida
(a) Plant body well differentiated into root, stem and leaves.
(b) Leaves megaphyllous, pinnately compound.
(c) Sporangia develop on the ventral surface of the sporophylls, usually aggregated into sori. e.g., Dryopteris,
Pteris, Pteridium, Polypodium, etc.

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(20) Economic importance

(i) Ornamental value : Many ferns are grown as ornamental plants in gardens for their large, Show and
graceful foliage. e.g., species of Lycopodium, Nephrolepis, Selaginella, Lygodium, Anemia, Cyathea etc.

(ii) Medicines : An anthelmintic drug is obtained from the rhizomes and petioles of the fern Dryopteris.
Lycopodium clavatum is used in skin diseases. Equisetum arvense has diuretic properties.

(iii) Food : The sporocarps of Marsilea are rich source of starch and used by tribals for their nutritive value.

(iv) Soil conservation : Plants like Selaginella are useful in soil conservation.

Important Tips

• The term Pteridophyta was first introduced by Haeckel in 1866.
• The term Cryptogams was coined by Linnaeus (1737) which means plants without seeds.
• Tracheophytes : Sinnott (1935) coined the term to include vascular plants (pteridophytes and seed plants).
• The chloroplasts of Selaginella contain pyrenoids.
• Stem of Selaginella kraussiana shows distelic condition.
• Smallest pteridophyte is Azolla whereas the largest is Cyathea/Alsophila (Tree ferns).
• Adiantum is commonly called 'Maiden hair fern'.
• Elaters : Elongated structures which help in spore dispersal. They have spiral bands of thickening for xerochasy. Elaters are epispore

appendages in horsetail Equisetum. Anthoceros has pseudoelaters.
• Cormophytes : Plants with distinction of stem, leaves and roots.
• Selaginella lepidophylla and S. pilifera are xerophytes and sold in the market as novelties.
• Salvinia is root less pteridophyte.
• Adiantum is commonly known as walking fern because it propagates vegetatively by its leaf tips. Some species of Adiantum are

Xerophytes.
• Meristeles are found in fern rhizomes.
• Selaginella oregana, Lycopodium squarrosum and Asplenium nidus are epiphytes.
• Rudimentry seed habit occurs in selaginella.
• Acrostichum aureum is a halophyte.
• Marsilea occurs as terrestrial, amphibious as well as aquatic plant.
• Azolla is an aquatic water fern used as biofertiliser. The alga – Anabaena fixes atmospheric nitrogen in symbiotic association with Azolla.
• Salvinia is an aquatic pteridophyte weed.
• Equietum is commonly known as Horsetails or Scouring rushes. A few species of Equisetum contain gold.
• Lycopodium is commonly known as club moss.
• In ferns, young leaves are protected by Ramenta.
• Vernation is arrangement of leaves in bud condition.
• Unbranched erect axis is called caudex.
• Brown scale are called ramenta.
• Selaginella is also Rnown as 'resurrection plants'.
• Stomium is the area on sporangial wall from which spores dehisce.
• Psilophytes (Cooksonia, Rhynia etc.) primitive pteridophytes of Silurian and Devonian period.
• Ophioglossum (Adder's tongue fern) has maximum number of chromosomes (2n = 1242) in plant kingdom.
• The vascular supply given for a leaf from the main stele is called 'leaf trace'.
• The parenchymatous region left behind in the main stele after the departure of the leaf trace is called 'leaf gap'.
• The vascular supply given out for a branch from main stele is called 'branch trace'.
• The parenchymatous region left out in the main vascular sylender due to departure of branch trace is called 'branch gap'.

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Gymnosperm.

(1) Introduction : Gymnosperm (Gk. Gymnos = naked ; sperma = seed) are the plants with exposed or
naked seeds or ovules. These plants represent the most ancient group of seed plants. They have been generally
placed in the division spermatophyta (seed bearing plants) along with angiosperms. They were not grouped
separately as gymnosperms. But Robert Brown (1827) separated them from angiosperms and placed under a
distinct group due to presence of unprotected ovules in them. The gymnosperm originated much earlier then
angiosperms. However, most of the members of this group have now become extinct and only few living forms are
known today. The living gymnosperm are generally grouped under four orders (Cycadales, Ginkgoales, Coniferales
and Gnetales).

(2) Distribution : Plants of Gymnosperms occur throughout the world. The group is presently represented by
only 900 living species. Of these, about 500 species belong to 'Conifers' or cone bearing plants. Several species of
conifer occur in north-west America and eastern and central China. In India several members are found in
Himalayas, Podocarpus and Cupressus in the central and Larix, Tsuga, Cephalotaxus in the eastern. The Indian
species of Ephedra are commonly found in Punjab, Rajasthan, Haryana and from Sikkim to Laddak. Gnetum sp.
occur in Kerala, Assam, Naga hills, Orissa, Sikkim, Burma, Thailand and China. Welwitschia is endemic to south-
west Africa. Ginkgo is native of South China.

(3) Habit : Living gymnosperms are mostly perennials, xerophytic, evergreen, arboreal and woody plants.
They grow as wood trees, bushy shrubs or rarely as climbers (e.g., Gnetales). None of them are herbs or annuals.

(4) External features

(i) The plant body is sporophyte and differentiated into root, stem and leaves.

(ii) The plant possess well developed tap root system. In some cases the roots are symbiotically associated
with algae (e.g., Coralloid roots of Cycas) or with fungi (e.g., Mycorrhizal roots of Pinus).

(iii) The stem is erect, aerial, solid, woody and branched (unbranched in Cycadales) but almost tuberous in
Zamia.

(iv) The leaves may be microphyllous or megaphyllous.

(5) Gymnospermous wood

(i) Manoxylic wood : Cambial activity is short lived, cortex and pith are broad, parenchymatous rays are
broad, wood is soft and commercially useless. e.g., Cycas.

(ii) Pycnoxylic wood : Cambial activity is long lived, cortex and pith are reduced, parenchymatous rays are
few, wood is hard and compact, wood is commercially most important and used as good quality timber. e.g., Pinus.

(6) Reproduction : Gymnosperms are heterosporous, i.e., produce two different kinds of spores – the male
microspores and the female megaspores. The spores are borne inside the sporangia. The two types of sporangia
are borne on special leaf-like structures, called sporophylls. The microsporangia (pollen sacs) are born on
microsporophylls (= stamens) and the megasporangia (ovules) are borne on megasporophylls (= carpels).

The sporophylls are usually aggregated in the form of compact structures called cones or strobili. The cones
are generally unisexual, i.e., the male cones are microsporangiate (pollen cones) and the female cones are
megasporangiate (seed cones). The male cones are short lived whereas the female cones are long lived. The female
cones remain attached on the plants for several years till the maturity or ripening of the seeds.

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(7) Pollination : The microsporangium (Pollen sac) produces numerous light pollen grain. Pollination is
anemophilous (wind pollination). The ovules are orthotropous and remain exposed on the megasporophyll. Each
ovule surrounded by integuments. It incloses the nucellus and a female gametophyte formed from the haploid
megaspore. The female gametophyte contains archegonia. The pollen grains are captured by the pollination drop
secreted by the micropyle of the ovule. When it dries, the grains are sucked in the pollen chamber. The pollen
grains now germinate. A pollen tube is formed due to elongation of the tube cell. In Cycas and Ginkgo the pollen
tube is haustorial in nature. The lower end of the tube bursts and releases the male gametes which fuse with the egg
to form the zygote.

(8) Fertilization : Fertilization occurs by siphonogamy, i.e. the male gametes are carried to the archegonia
through pollen tube (except in Cycas where pollen tube functions as haustorium and fertilization occurs by
zoodiogamy). Fertilization thus takes place in the absence of external water.

(9) Embryogeny : The zygote undergoes free-nuclear divisions in Cycas followed by wall formation. There
are no free-nuclear divisions in Sequoia and Gnetum. The embryo is soon differentiated into an upper haustorial,
middle suspensor and lower embryonal regions. In Pinus, on the other hand, the zygote gets differentiated into
four tiers of four cells each, designated as open tier, rosette tier, suspensor tier and embryonal tier. Cleavage
polyembryony is seen in Pinus. The embryonal part shows differentiation of radicle, hypocotyl, cotyledons and
plumule.

(10) Seed : As a result of fertilization the ovule develops into a seed. The integument forms the seed coat.
The outer fleshy layer of the integument forms the testa whereas the middle stony layer gives rise to tegmen. The
nucellus persists as a cap like perisperm. In Taxus a fleshy aril is also present at the base as a cup like structure.
The seeds of gymnosperms comprise tissue of three generations namely parent sporophytic (integument and
nucellus), gametophytic (endosperm) and second sporophytic (embryo).

(11) Living fossils : When a group of plants is represented by a single genus or species while rest of the other
representatives of the group have become extinct and fossilized the long surviving individual is called a living fossil
e.g., Ginkgo biloba. However, Cycas is also regarded as a living fossil because most of the cycad species are
confined to tropical and subtropical region and the group is becoming endangered. Therefore, cycads have been
referred as reptiles of plant kingdom or panda of vegetable kingdom.

(12) Classification : Robert Brown (1827) recognised the gymnosperms as a group distinct from
Angiosperms. However, Bentham and Hooker (1862-83) in their 'Genera Plantarum' placed them between
Dicotyledonae and Monocotyledonae, Chamberlain (1934) divided gymnosperms into following two sub-classes.

(i) Cycadophyta

(ii) Coniferophyta

(i) Sub-class I. Cycadophyta : These are characterised by the presence of unbranched stem and large foliage
leaves. Internally, the stem has large pith and cortex but the wood is relatively small. It includes following 3 orders.

Order 1. Cycadofilicales : It is a group of fossil plants. These plants resembled with ferns, hence they were
given the name Pteridospermae (i.e., seed bearing ferns). e.g., Lyginopteris, Medullosa.

Order 2. Bennettitales or Cycadeoidales : It is also a group of fossil forms. These plants resembled with
modern cycads. e.g., Cycadeoidea, Williamsonia.

Order 3. Cycadales : It includes both living and fossil forms. e.g., Cycas, Nilssonia, Zamia.

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(ii) Sub-class II. Coniferophyta : These are characterised by long profusely branched stem and simple
small leaves. In stem the amount of wood is much more than cortex and pith. It includes following four orders.

Order 1. Cordaitales : All the members of this order are extinct. e.g. Cordiates, Dadoxylon.

Order 2. Ginkgoales : All the members of this order, except for Ginkgo biloba are extinct. Ginkgo biloba is
a medium sized tree with branched stem and bilobed leaves. Because of the resemblance of the leaves of this plant
with those of Adiantum (maiden hair fern), the name Maiden hair tree has been given.

Order 3. Coniferals : The order includes both fossils and present day forms. e.g., Pinus, Cedrus, Sequoia.

Order 4. Gnetales : Gnetales are modern group consisting of living forms. The order differs from other
gymnosperms in the presence of vessels in the xylem. e.g., Ephedra, Gnetum, Welwitschia.

(13) Economic importance

(i) Ornamentals : Some of the gymnosperms are grown in the gardens in different parts of the world e.g.,
Cycas revoluta, Ginkgo biloba, Auraucaria cookii, A. bidwilli, Biota orientalis, Cupressus sp., Juniperus sp., Thuja
sp., Taxus baccata, Cryptomeria japonica etc.

(ii) Wood : Several plants of this group yield useful timber. The wood of Cedrus deodara is used for making
railway sleepers. It is also used as a structural timber and making bridges. The wood of Callitris verrucosa, Pinus
roxburghii, P. wallichiana, P. pinaster, P. lambertiana etc. is used for making furniture. Juniperus virginiana wood is
used for making pencils. The gymnosperm Agathis australis is perhaps the largest timber producing tree of the
world. Soft wood of many gymnosperms is used for making toys.

(iii) Resins : Several conifers yield resin which is obtained by tapping. By distilling the oleoresin obtained
from pines. The resins are of three types namely hard resins, oleoresins and gum-resins. Several hard resins
are obtained from living and fossil conifers which are as under :

(a) Copals : Kauri copal is obtained from Agathis australis and manila copal from Agathis alba.

(b) Amber : It is obtained from the fossil conifer Pinites succinifera.

(c) Sondarac : This pale-yellow resin comes from Callitris quadrivalis and Tetraclinis articulata. The
turpentines are oleoresin which are also contributed by conifers. An important source of turpentine is Pinus
australis, P. ponderosa and P. caribeae. Besides, some of the following products of turpentine nature are also
obtained from conifers :

 Canada balsam : It is obtained from Abies balsamaea.

 Spruce gum : It is obtained from Picea rubens.

 Bordeaux turpentine : It is obtained from Pinus pinaster.

 Venetian turpentine : It is obtained from Larix decidua.

(iv) Essential oils : They are obtained from several plants. These oils are used mainly in perfumery, soap
industry etc. The important oil yielding plants are Tsuga canadensis, Picea glauca, Abies siberica and Cedrus
deodera. The oil obtained from Juniperus virginiana (cedar wood oil) is also used in microscopic work.

(v) Paper industry : The wood of several gymnosperms, particularly those of conifers is used in paper
industry e.g., Abies pindrow, Picea smithiana, Cryptomeria japonica, Pinus roxburghii, Tsuga canadensis etc.

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(vi) Edible : The seeds of Pinus geradiana (chilgosa) and P. roxburghii are edible. Sago is obtained from
Cycas revoluta. The seeds of Cycas sp. are ground and used in the preparation of many edible products.

(vii) Medicinal use : Species of Ephedra yield an alkaloid called ephedrine. It is used in the preparation of
medicines for the treatment of cough, asthma and bronchitis.

Important Tips

• The term gymnosperm was introduced by Theophrastus.
• Cycas ovules are sessile and orthotropous. The ovules of C. circinalis are about 6 cm wide whereas those of C. thouarsii are 7 cm wide.

They are largest ovules in the plant kingdom.
• The egg of Cycas is largest among all living plants. It is about 1/2 mm in diameter in Cycas circinalis.
• Sperms of Cycas revoluta are largest in the plant kingdom and measure about 200 to 300µ wide. They are top-shaped, multiciliate with

spiral band of cilia. (First observed by lkeno, 1896).
• World's tallest gymnospermous tree is Sequoia sempervirens, which measures about 368.5 ft. in height (found in Red wood park of

California).
• The largest gymnospermous tree (in girth) is Sequodendron, which measure about 13-16 meters in diameter. However, Taxodium

mucronatum (the big tree of Tule) is not too tall but sometimes measures about 24 meters in diameters.
• The longest (oldest) gymnospermous tree (in age) is Pinus longavaea, which is about 4900 years old.
• The smallest gymnosperms is Zamia pygmia, which has underground tuberous stem.
• In gymnosperm xylem is generally made up of tracheids (Non-porous) but vessels have been observed in Gnetum, Ephedra and

Welwitschia.
• The primitive haplochelic type of stomata are found in Cycas, Pinus, Ginkgo, Ephedra etc.
• The plants of Welwitschia are unique in Gymnosperms.
• The wood formed may be in one ring due to persistent cambium. Such a wood is called as monoxylic. e.g., Pinus.
• The wood is formed in more than one ring due to ephimeral nature of cambium. Such a wood is called as polyxylic. e.g., Cycas.
• The female cone of Pinus takes three years for complete maturity.
• The pollen grain of Cycas are shed at three celled stage while in Pinus pollen is shed at four celled stage.
• Prothallial cell absent in pollen grains of Welwitschia.
• Dwarfism is seen in many gymnosperms perphaps due to wind velocity. e.g., Picea engelmannaii (15 cm).
• In Pinus, pollen grains are winged.
• All gymnosperms bear unitegmic orthotropous ovules.
• Cycas wood is mano and monoxylic, where wood of Pinus is pycnoxylic.
• In gymnosperm endosperm is haploid and develops before fertilization.
• About two hundred million years ago, the gymnosperms formed the dominant vegetation on the earth.
• The only gymnosperm showing limited growth is Welwitschia (45 cm. tall).
• The ramnent nucellar tissue present within the seed covering of embryo is called perisperm.
• Cycas revoluta is commonly called 'sago palm'.
• Pinus gerardiana is commonly called 'chilgoza pine'.
• Embryo sac of gymnosperm is haploid.
• Monkey's puzzle is a common name of Araucaria embricata.
• In gymnosperm, the arrangement of megaspore tetrad is linear.
• Archegonia are not formed in Gnetum and Welwitschia.
• Neck canal cell absent in archegonia.
• Sulphur shower is due to pollen of Pinus/Cedrus.
• In gymnosperms phloem lacks companian cells.

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Angiosperms.

(1) Introduction : The angiosperms, or flowering plants, constitute the most dominant and ubiquitous
vascular plants of present day flora which changed the green and yellow melancholy of the earth's vegetation by the
colourful brightness and fragrance of their flower. The term angiosperm means 'enclosed seed' because the ovules
or potential seeds are enclosed within a hollow ovary. In this respect they are considered most highly evolved and
advanced as compared with the naked seeded gymnosperms.

(2) Characteristic features

(i) Angiospermous plants grow in almost every kind of habitats. In the deserts, these plants grow, flower, shed
seeds and complete their life cycle in a few weeks of rainy season. Some flowering plants like Zostera, occur in
shallow seas. A small orchid even lives underground. It survives as a saprophyte on decaying organic matter
because of the mycorrhizal association which helps to obtain nourishment. In rain forests, some plants grow on the
branches of other plants but do not obtain water or food from them. They are called epiphytes (e.g., Vanda).

(ii) The angiospermous leaves show reticulate or parallel venation forming areoles. The libriform fibres are present in
the xylem and the companion cells are present in the phloem. The true vessels are present in the xylem of angiosperms.

(iii) The angiosperms produce flowers which normally consist of 4 whorls of appandages – the two outer
accessory and reproductive structure such as sepals and petals and the two inner essential parts – stamens and carpels.

(iv) The stamens (microsporophylls) are bilaterally symmetrical. Each stamen consists of a filament and an anther.

(v) The anthers produce tectate pollen grains with exine differentiated into rod-like columellae covered by a tectum.

(vi) In angiosperms, the insects and animals also act as pollinating agents. For this purpose the flowers possess
bright and showy petals, edible pollen and nectar.

(vii) The carpels (= megasporophylls) are rolled and partly sterile so that they enclose the ovules within a
hollow ovary that is connected with the stigma and style.

(viii) The female gametophyte is highly reduced and consists of single egg cell, two synergids, three antipodals
and two polar nuclei. The archegonia are absent.

(ix) The most characteristic feature of angiosperms is double fertilization.

(a) The male gamete fuses with the egg producing diploid zygote that develops into embryo or new sporophyte.

(b) Another male gamete fuses with the polar nuclei (triple fusion) resulting in the formation of triploid endosperm.

(x) After fertilization, the ovules ripens into seeds and ovary ripens into fruits.

(3) Size
(i) The smallest angiosperm is Wolffia. The plant body of Wolffia consists of tiny flat oval green stem
(phylloclade) having a few small roots. The plants are about 1 mm in diameter and found free floating in aquatic
habitats like ponds, etc.

(ii) The tallest angiosperm is Eucalyptus. Their trees may attain a height upto 100 meters or more.

(iii) Banyan (Ficus bengalensis) tree covers a large area. It's slanting aerial branches spread in all directions.
The tree spreads with the help of prop or pillar roots.

(4) Longevity : Based on the duration of life, the plants are divided into following 4 categories :
(i) Ephemerals : This category includes the plants which live only for a few weeks because of a very short
growing season. Such plants are found near deserts or in very cold countries. For example, Arabidopsis species
have a life span of 20–28 days.

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(ii) Annuals : The plants of this category live and complete their life-cycle in a single favourable season.
During this period, they grow in size, produce flowers, shed their seeds, undergo senescence and die. They pass the
unfavourable period in the form of seeds. Many crop plants (e.g., wheat, rice, maize, etc.) are annuals. The smallest
angiosperm – Wolffia is an aquatic annual.

(iii) Biennials : The plants of this category complete their life-cycle in two favourable seasons (i.e., in two
years). They grow vegetatively in the first season and produce flowers and set seeds in the next. Often they produce
some storage organs, as in the sugar beet, where food is stored in their swollen roots.

(iv) Perennials : Plants of this category live for more than two years. Generally they live for many years and
bear the flowers and fruits during specific seasons. Some perennials continue their vegetative growth for several
years and produce fruits and seeds only once in their life time, e.g., Agave, Bamboos, etc. They are called
monocarpic. Others produce flowers and fruits every year after attaining a definite stage of maturity, e.g., Mango,
Lemon, Apple, etc. Such plants are called polycarpic.

(5) Habit : Depending upon the habit of plants, the angiosperms belong to following categories –

(i) Herb : These are small, soft, non-woody plants without persistent parts aboveground. The height of plants
usually reaches upto 1 m. The plants may be annual (Brassica), biennial (Sugar beet) or perennial (Canna). The
perennial herbs usually possess underground rhizomes which form the new aerial shoots every year. The plants of
banana are perennial herbs.

(ii) Shrubs : These are woody plants of relatively low height (1-4 m). They typically branch at or near the
base and do not have a main trunk, e.g., Rose. They are mostly perennial.

(iii) Trees : These are perennial woody plants with one main trunk. The trunk may or may not be branched.
These are of the following types :

(a) Caudex : The stem is unbranched and usually bears a crown of leaves at the apex. e.g., Date-palm.

(b) Excurrent : The lower part of stem is thicker which gradually tapers above. Branches arise from the main
stem in acropetal succession and plant appears conical e.g., Pinus.

(c) Deliquescent : The apical bud of the main stem dies after some time and branches and sub-branches
spread in different directions. e.g., Tamarindus, Ficus.

(iv) Culms : In these plants, nodes and internodes are extremely clear. Internodes of such plants are usually
hollow. These plants are grasses but cannot be considered as herb or shrub or tree. e.g., Bambusa (Bans).

(6) Habitat : Warming (1895) divided the plants, on the basis of their adaptation to water, into four major
groups – hydrophytes, mesophytes, xerophytes and halophytes. A fifth group epiphytes can also be included.

(i) Hydrophytes : The plants which grow in aquatic habitats are called hydrophytes. They are further grouped as –

(a) Submerged (e.g., Hydrilla)

(b) Attached floating (e.g., Nymphaea)

(c) Free-floating (e.g., Eichhornia, Wolffa)

(d) Amphibious or partly emerged hydrophytes (e.g., Sagittaria).

(ii) Mesophytes : These are the plants which grow under moderate moisture and temperature conditions.
They have no special adaptations to grow either in very dry or in very wet conditions (e.g., Sun flower, Brassica).
These plants do not possess special adaptations to reduce transpiration.

(iii) Xerophytes : The plants which grow in dry or xeric habitats (i.e., under deficient supply to available
water) are called xerophytes. These plants face acute shortage of water and therefore, develop morphological,

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structural and physiological adaptations in order to survive under such habitats. The adaptations in plants are
mainly to check the transpiration and survive under acute shortage of water. e.g., Cynodon (Doob grass),
Casuarina, Euphorbia tirucalli, Asparagus, etc.

(iv) Halophytes : Halophytes are those plants which grow in saline habitats, i.e., in salt marshes, alkaline
soils, river estuaries, saline ponds near seashore or sandy and heavy soils having excess of salts. In such habitats,
the water is present in sufficient amount but due to high osmotic concentrations it is physiologically not available to
normal plants. Such conditions are said to be physiologically dry. e.g., Spartina, Atriplex, Portulaca etc.

(v) Epiphytes : These are the plants which grow on other plants for space only. The plants are autotrophic
and occur both in aquatic and terrestrial habitats. e.g., Vanda (an orchid).

(7) Modes of nutrition : On the basis of modes of nutrition plants are classified as follows –
(i) Autotrophs : These plants manufacture their organic matter from inorganic matter.
(a) Photoutotrophs : These are green coloured due to the presence of chlorophyll. In the presence of light
they are capable of synthesizing their food from CO2 and H2O. e.g., Mango, Mustard etc.
(b) Chemoautotrophs : Those plants which synthesize their food from CO2 and H2O by using energy
product in the chemical reactions. e.g., Many bacteria.
(ii) Heterotrophs : They are either unable to photosynthesize their food or are unable to take their water and
minerals directly from the soil or unable to synthesize protein. They are classified as follows :
(a) Parasites
(b) Saprophytes
(c) Symbionts
(d) Insectivorous plants
A detailed discussion of these group is given in chapter "Plant nutrition".
(8) Reproduction : (See in embryology).
(9) Classification : The plants of Angiosperms divided into two major groups as – Dicotyledons and
Monocotyledons.
(i) Dicotyledons : They are show following distinguished characteristics.
(a) Tap roots found in the members of this group.
(b) The leaves in members of these class exihibit reticulate (net like) venation.
(c) The flowers are tetramerous or pentamerous having four or five members in the various floral whorls,
respectively.
(d) The vascular bundles arranged in a ring, numbering 2–6, open and with cambium.
(e) The seeds of dicotyledons are with two cotyledons as the name indicate.
(ii) Monocotyledons : They are show following distinguished characteristics :
(a) Adventitious roots found in the members of this group.
(b) The leaves are simple with parallel venation.
(c) The flowers are trimerous having three members in each floral whorl.
(d) The vascular bundles scattered in the ground tissue, many in number, closed and without cambium.

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(e) The seeds of monocotyledons are with one cotyledons as the name indicate. e.g., Cereals, bamboos,
sugarcane, palms, banana, lilies and orchids.

(10) Economic importance

(i) Food : Flowering plants are the major sources of food. They produce cereals such as wheat (Triticum
aestivum), rice (Oryza sativa), maize (Zea mays), barley (Hordeum vulgare), oat (Avena sativa), etc. pulses such as
pigeon pea or Arhar (Cajanus cajan), gram (Cicer arietinum), pea (Pisum sativum), Soyabean (Glycine max), green
gram (Vigna radiata, vern. mung), black gram (Vigna mungo, vern. urd), etc ; Vegetables such as potato (Solanum
tuberosum), tomato, carrot, cabbage, cauliflower, etc ; Fruits such as apple ; mango, grapes, banana, guava,
pears, melons, etc. and nuts such as cashewnut, walnut, almond, etc.

(ii) Edible oils : Flowering plants are the main source of edible oils used for cooking. These are obtained from
ground nut (Arachis hypogea), mustard (Brassica campestris), sunflower (Helianthus annus), coconut (Cocos nucifera), etc.

(iii) Spices : Common spices are obtained from various parts of flowering plants such as coriander
(Coriandrum sativum vern. dhania), chillies (Capsicum frutescens), cinnamon (Cinnamomum zeylanicum, vern.
dalchini), cloves (Syzygium aromatica, vern. laung), cara way (Carum carvi, vern. jeera), fennel (Foeniculum
vulgare, vern. saunf), black pepper (Piper nigrum, vern. Kali mirch), etc.

(iv) Timber : Many angiospermous tree, particularly dicotyledons, yield valuable hard wood which is used as
timber. The important timber producing plants are – teak (Tectona grandis), sal (Shorea robusta), oak (Quercus
alba), sisso or sisham (Dalbergia sisso), sandal wood (Santalum album), etc.

(v) Fibres : Fibres of different qualities are obtained from various species of flowering plants for e.g. :

(a) Textile fibres are obtained from cotton (Gossypium barbadense, Gossypium herbaceum, etc.)

(b) Rough fibres are obtained from flax (Linum usitatissimum), hemp (Cannabis sativa), sunn hemp
(Crotolaria juncea), etc. These fibres are used for making ropes and gunny bags.

(c) Jute is obtained from Corchorus sp.

(d) Husk of unripe coconut (Cocos nucifera) is used to obtain coir.

(vi) Beverages : Tea (Camellia sinensis = Thea sinensis), coffee (Coffea arabica) and cocoa (Theobroma
cacao) are the common beverages obtained from the flowering plants.

(vii) Medicines : Our Indian system of medicine (Ayurveda) utilises many flowering plants for the cure of
various ailments. Even today a large number of advanced medicines are prepared from these plants. Some of the
important medicinal plants are – Aconitum napellus (aconite), Atropa belladona (belladona), Cinchona sp.
(quinine), Withania somniferum (asvgandha), etc.

(viii) Others : There is a long list of useful articles such as paper, rubber, volatile oils, tobacco, etc., which we
get from flowering plants. sugar is obtained from sugarcane (Saccharum officinarum) and sugarbeet (Beta vulgaris).
A large number of plants are grown in the gardens as ornamentals.

Important Tips

• Bamboo or Agave are monocarpic perennial plants.
• A small archid grows underground as a saprophytes.
• Vessels are major water conducting cell in angiosperm.
• Double fertilization is a unique character of angiosperm.
• It is believed that Bodhi tree at Gaya is about 2000 years old.
• Anthophytes : Plants with flower/ flowering plants.
• Marine angiosperm : Zostera, Thalassia.
• National tree : Ficus bengalensis (Banyan).

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Introduction.

Angiospermic or flowering plants show a great variety of shape, size and form. The size ranges from the
minute Wolffia and Lamna (0.1cm) to the tall Eucalyptus (up to 100 metre) and large sized Banyan (Ficus
bengalensis). In habit, they range from herbs and shrubs to trees.

Morphology (Gr. Morphos = Form; logos = Study) is the branch of science which deals with the study of form
and structure. In botany, it generally means the study of external features, forms and relative positions of different
organs on plants.

It is virtually impossible to recognise and know all the flowering plants even for a professional taxonomist.

However, a student of botany takes the help of morphology for Flower Bud
recognition, identification and classification of plants. Some distinct

morphological features are most significant in the study of Fruit

phytogeography, phylogeny and evolution. Seeds Axil
Parts of a flowering plant : Flowering plants consist of a long Flowering shoot
(from terminal bud) Shoot system

cylindrical axis which is differentiated into underground root system and

an aerial shoot system. The root system consists of root and its lateral

branches. The shoot system has a stem, a system of branches and leaves. Lateral bud Node
The different parts of a plant are called organs. Organs are differentiated Internode
into two types, vegetative and reproductive. Vegetative organs take part Leaf

in nourishing and fixing the plant, viz., root, stem, leaves. Reproductive Stem Ground level
organs are required in multiplication. They comprise flowers, fruits and
seeds (formed inside fruits). Organs similar in basic internal structure and Lateral root Root system
origin which may appear different and perform different functions are
called homologous organs. The relationship amongst these organs is Main or tap
called homology. Organs performing a similar function or having a root

Fig : Morphology of a angiosperm plant

similar external form but different internal structure and origin are termed as analogous organs. The relationship

in analogous organs is called anology.

The root.

The root is usually an underground part of the plant which helps in fixation and absorption of water. The root
with its branches is known as the root system.

(1) Characteristics of the root

(i) The root is the descending portion of the plant axis and is positively geotropic.

(ii) It is non-green or brown in colour.

(iii) The root is not differentiated into nodes and internodes.

(iv) As a rule the root does not bear leaves and true buds.

(v) Usually the root tip is protected by a root cap.

(vi) The root bears unicellular root hairs.

(vii) Lateral roots arise from the root which are endogenous in origin (arises from pericycle).

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(2) Parts of the root : From the tip of the root upwards, the following parts can be traced in root.

(i) Region of root cap : The tip of the root is called calyptra or root cap. It is for protection of root tip against
any injury. It is formed from meristem called calyptrogen. Pandanus is the only plant with multiple root caps. In the
aquatic plants like Pistia, Lemma and Eicchornia instead of root caps, they have root pockets for buoyancy. The
root caps are absent in parasites and mycorrhizal roots.

(ii) Region of cell elongation : The region of cell division lies partly within Region of
and partly beyond the root cap. This is the meristematic region of the root which maturation
produces new cells by cell division.

(iii) Region of root hairs : This region is present above the region of Region of
elongation. In this region the epidermal cells produce many tubular, unicellular root hairs
outgrowths called root hairs. This is also called Piliferous region. Water absorption
mostly takes place through this region. The root hairs are absent in many aquatic Region of cell
plants. elongation

(iv) Region of maturation : Above the root hair zone, mature region is Meristematic
present. This region consists of permanent cells. Lateral roots are produced region
endogenously from the mature region. Conduction of water and mineral salts takes
place through this region. Region of
root cap
Fig : Regions of the root

(3) Types of root system : The root system is generally of two types :

(i) Tap root system

(ii) Adventitious root system

(i) Tap root system : The tap root system develops from radicle of the germinating seed. It is also called the
normal root system. The radicle develops into a primary root which grows vertically downwards and become the
tap root. The tap root is the true root that produces many lateral roots endogenously which grow obliquely. The tap
root system is present in dicotyledonous plants.

(ii) Adventitious root system : The root system that develops from any part of the plant body other than
the radicle is called the adventitious root system. It is mostly seen in monocotyledonous plants. In grasses, fibrous
root system is present. It is a type of adventitious root system. In this case the primary root formed from the radicle
disappear soon. Then many slender roots develop from the base of the stem as cluster of fibres, hence called the
fibrous root system. Shrub like monocots needs additional support because of the adventitious root. e.g., Stilt root
in sugarcane.

Modification of roots.

Sometimes the root performs other functions other than fixation, absorption and conduction so get modified
structurally. Both tap roots and adventitious roots may undergo such modifications. There are many types of root
modifications.

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(1) Modification of tap roots

Root modification

Storage roots Branched root

Conical Fusiform Napiform Tuberous Nodulated root Pneumatophores

(i) Storage roots : In some plants, the primary tap roots are modified for storing reserve food materials. The
secondary roots remain thin and they are absorptive in function. The storage roots are usually swollen and assume
various forms :

(a) Conical : The swollen root is broad at the base and tapers gradually towards the apex giving a shape of
cone, e.g., Carrot.

(b) Fusiform : The root is swollen in the middle and
narrow towards both its base and apex giving a shape of
spindle, e.g., Radish (Raphanus sativus). Half or less than
half portion towards the base of fusiform root is formed by
hypocotyl.

(c) Napiform : The root is nearly globular or spherical (A) (B) (C) (D)
in shape. The basal portion of root is much swollen which
suddenly tapers towards the apex giving a top-shaped Fig : Modifications of tap root : (A) Conical root of carrot,
appearance, e.g., Turnip (Brassica napus, vern, Shalgam) (B) Fusiform root of radish, (C) Napiform root of turnip,
and Beet (Beta vulgaris, vern. Chukandar).
(D) Tuberous root of tapioca

(d) Tuberous : The storage root having no definite shape is called tuberous, .e.g., Mirabilis jalapa (4 O’clock
plant), Trichosanthes (vern. Parwal), Echinocystis lobata (The tuberous root is lobed and weighs as much as 22 kg.).

(ii) Branched roots : They are following types :

(a) Nodular roots : The primary tap roots and its branches of Breathing
leguminous plants, i.e., plants belonging to sub-family papilionatae of pores
the family leguminosae (e.g., Pea, Gram, Ground nut, Beans etc.), bear
nodule like swellings, called root nodules. Pneumato
phore
They are red in colour due to the presence of leg-haemoglobin.
The nodules are inhabited by nitrogen fixing bacteria called Rhizobium Mangrove
leguminosarum. It converts atmospheric nitrogen into nitrates and plant
supply them to the plant. In turn Rhizobium gets nutrients and shelter
from the plant. This type of association between the bacterium and Pneumatophore
leguminous plant for mutual benefit is known as symbiosis and the
organisms involved are called symbionts. This association is also Normal root

(A) (B)

Fig : Pneumatophores :
(A) Plants showing pneumatophores
(B) Part of pneumatophores showing

breathing pores

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called mutualism which is obligatory for both i.e., for bacteria and leguminous root.

(b) Pneumatophores or Respiratory roots : Roots also breathe and as such they also require air for
gaseous exchange. Normally, the soil has a large number of small air spaces between the soil particles. This air is
utilized by the plants for their respiration. But the roots of some plants growing in saline marshes (mangrove plants)
suffer from the lack of oxygen. This is due to the water logged condition of the soil. To cope with this situation some
root branches grow vertically upwards. They become aerial and negatively geotrophic. These roots bear many
minute pores called pneumathodes towards their upper ends. Gaseous exchange takes place through
pneumathodes. Such aerial, porous negatively geotrophic roots which help in gaseous exchange are called
breathing or respiratory roots, breathing roots or pneumatophores roots or pneumatophores e.g., Sonneratia,
Heritiera, Rhizophora, Avicennia and Ceriops etc. and are found in sundarbans of West Bengal.

(2) Modification of adventitious roots

Root modification

For physiological or vital functions For mechanical functions
(a) Stilt roots
(a) Storage roots (b) Prop roots
(1) Tuberous roots (c) Buttress roots
(2) Fasciculated roots (d) Climbing roots
(3) Nodulose roots (e) Floating roots
(4) Moniliform roots (f) Contractile roots
(5) Palmate roots (g) Root thorns
(6) Annulated roots

(b) Epiphytic roots
(c) Parasitic roots
(d) Saprophytic roots
(e) Photosynthetic roots
(f) Reproductive roots

(i) For physiological or Vital functions

(a) Storage roots : The roots where adventitious roots become swollen to store food. They are following types :

• Tuberous roots : These adventitious roots are swollen without any definite shape e.g., Ipomoea batata
or (sweet potato).

• Fasciculated roots : These are tuberous roots arising in cluster from the base of the stem. e.g., Dahlia,
Ruellia (Menow weed), Asparagus (Asparagus fern) etc.

• Nodulose roots : These roots become swollen at their tips due to accumulation of food e.g., Maranta sp.
(Arrowroot), Curcuma amanda (Mango – ginger).

• Moniliform or Beaded roots : These adventitious roots are swollen at frequent intervals. This gives the
root a beaded appearance. e.g., Portulaca (Rose moss) Momordica (Bitter gourd) Cyperus (Guinea rush).

• Palmate tuberous roots : In Orchis there is a pair of succulent tuberous root, one of which perishes
every year while another new one is formed by its side. Such orchid roots may sometimes be of palmate shape,
therefore, called palmate roots.

• Annulated roots : The roots of a medicinal plant, Ipecac (Cephaelis ipecacuanha) yields emetine that
looks like discs placed one above another, therefore, called annulated.

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(A) (B) (C) (D) (E) (F)

Fig : Modification of adventitious root (for food storage) : (A) Tuberous root of sweet potato
(B) Fasciculated roots of dahila, (C) Moniliform root of Momordica, (D) Nodulose roots of

mango ginger, (E) Palmate roots of Orchis, (F) Annulated roots of Ipecac

(b) Epiphytic roots : These roots are also called ‘hygroscopic roots’. These roots develop in some orchids
which grow as epiphytes upon the trunks or branches of trees. They hang freely in the air and absorb moisture with
the help of special sponge like tissue called velamen. Velamen is modification of epidermis. e.g., Venda,
Dendrobium etc.

(c) Parasitic or Haustorial roots : Plants which depend on plant partially or totally for their food material
are known as parasites. The roots of parasitic plants, which penetrate into the host tissues to absorb nourishment,
are called haustorial roots. The haustorial roots of Cuscuta (Dodder, vern. Amarbel) penetrates the host upto
phloem and xylem to absorb organic food, water and minerals. The haustorial roots of partial parasite – Viscum
(Mistletoe) penetrate upto xylem of host to absorb water and minerals.

Parasite which absorb their nutrients from the host stem are known as stem parasites while those which absorb
their nutrients from the host root are know as root parasite.

(d) Saprophytic roots : They are also called mycorrhizal roots as here roots are associated with fungal
hyphae either superficially (ectomycorrhizae) or internally (endomycorrhizae) for absorption of water and minerals.
e.g., Monotropa and Sarcodes.

(e) Photosynthetic or Assimilatory roots : These are green, aerial, adventitious roots which prepare food
materials by photosynthesis are called photosynthetic roots or assimilatory roots e.g., Taeniophyllum, Trapa and
Tinospora. In some epiphytes like Taeniophyllum, the stem and leaves are absent. The entire plant is represented
by thin green, ribbon like roots which contain velamen. These roots absorb moisture from the atmosphere and
manufacture food materials by photosynthesis. Since the roots are green and perform photosynthetic activity, these
roots are called photosynthetic roots or assimilatory roots.

(f) Reproductive roots : Some fleshy adventitious root develop buds which can grow in to new plants. These
are called reproductive root. These roots serve as means of vegetative propagation. e.g., Sweet potato, Dahlia etc.

(ii) For mechanical function

(a) Stilt roots : The aerial, adventitious obliquely growing roots that develop from the lower nodes of the
stem to give additional support are called stilt roots. This roots bear several large overlapping root caps called
multiple root caps. e.g., Sugarcane, Pandanus, Rhizophora, Sorghum and Maize. Pandanus (screw pine) is a
common sea shore plant.

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They also help in the absorption of water and minerals from the soil. In monocots, these roots arise in whorls
from a few basal nodes of stem.

(b) Prop roots : These adventitious aerial roots arise from horizontal aerial branches of the trees like Ficus
bengalensis (Banyan). Initially, they are hygroscopic in function, become red in moist condition and possess root-
caps at their apieces. They grow vertically downward, penetrate the soil, become thick and assume the shapes of
pillars. They provide support to the spreading branches of tree. Sometimes the main trunk dies and it is replaced by
prop roots which assume the shapes of trunks.

In India, the biggest banyan tree having large number of prop roots are found at Indian Botanical Gardens,
Kolkata and Kadiri (Andhra Pradesh).

(c) Buttress roots : The horizontal plank like aerial, adventitious roots that develop at the base of the stem to
give additional support are called buttress roots or ballast roots, e.g., Terminalia and Salmalia. In some huge and
heavy trees, plank like roots develop at the base of the stem on the soil surface. These roots give additional support
and act like ballasts. Hence these roots are called ballast roots.

(d) Climbing roots : The aerial adventitious roots that arise from the nodes or internodes of weak stemmed

plants to climb up their support are called climbing roots, e.g., Pothos, Piper betel, Vanilla

and Hedera. Many weak stemmed plants climb up their supports in order to expose their

leaves efficiently to sunlight. In Pothos and Hedera, climbing roots develop all over the Climbing
stem. In Vanilla, single tendril like root arise at each node. Hence they are called tendrillar roots

roots. In Piper betel, many short branched, adventitious roots arise at each node. These

roots are called clinging roots.

(e) Floating roots : These roots develop from the nodes of floating aquatic plants Fig : Climbing root of
like Jussiaea (=Ludwigia). They store air, become inflated and spongy, project above the Piper betel
level of water, make the plant light and function as floats.

(f) Contractile or Pull roots : Some roots of plants with underground stems contract or swell so that the
aerial shoots are kept in a proper depth in the soil. These roots are called contractile or pull roots, e.g., Canna,
Crocus, Allium, Lilium, Freesia, etc.

(g) Root thorns : In aroids like Pothos and many palms (Acanthorhiza and Iriartea) the adventitious roots
become hard and pointed hence called root thorns.

The stem.

The stem develop from the plumule of the germinating seed. Normally it is the aerial part of the plant body.
The stem with it's branches, leaves, buds, flower and appandages is known as shoot system.

The stem shows the differentiation of nodes and internodes. The place where the leaf develops on the stem is
called the node. The portion of the stem between two successive nodes is called the internode.

(1) Characteristics of stem

(i) Stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo.

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(ii) It is generally erect and grows away from the soil towards light. Therefore, it is negatively geotropic and
positively phototropic.

(iii) The growing apex of stem bears a terminal bud for growth in length.
(iv) In flowering plants, stem is differentiated into nodes and internodes. A node occurs where leaves are
attached to the stem. Internode is the portion of stem between the two nodes.
(v) The lateral organs of stem (i.e., leaves and branches) are exogenous in origin (from cortical region).
(vi) The young stem is green and photosynthetic.
(vii) Hair, if present, are generally multicellular.
(viii) In mature plants, stem and its branches bear flowers and fruits.
(2) Diverse forms of stem

Aerial stems
(Epiterranean stems)

Reduced Erect Weak

(a) Culm
(b) Caudex (Columnar)
(c) Excurrent
(d) Decurrent (Deliquescent)

Upright weak stems Prostrate weak stems

Twiners Climbers Trailers Creepers

(i) Tendril climbers (i) Procumbent (i) Runners
(ii) Root climbers (ii) Decumbent (ii) Stolons
(iii) Scramblers (iii) Diffuse (iii) Offsets
(iv) Lianas

(i) Reduced stems : In some plants, the stem is in the form of a reduced small disc which is not differentiated
into nodes and internodes. e.g., (a) A reduced green-coloured disc-like stem lies just above the base of fleshy roots
of Radish, Carrot and Turnip ; (b) Green-coloured small discoid stem occurs in free-floating Lemna, Spirodela and
Wolffia; (c) Highly reduced non-green discoid stem occurs at the base of Onion and Garlic bulbs, etc.

(ii) Erect stems : Majority of angiosperms possess upright, growing-ascending, vertically-erect stems. They
are fixed in the soil with the help of roots. Erect stems belong to four categories :

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(a) Clum : Erect stems with solid nodes and hollow internodes. The nodes are swollen giving the stem a
jointed appearance e.g., Bamboo (Bambusa arundinacea) and wheat (Triticum vulgare).

(b) Caudex : The main stem remains unbranched and bears a crown of leaves at its top. e.g., Coconut
(Cocos nucifera), Palm, etc.

(c) Excurrent : The main stem is trunk like. It is thickest at
the base and gradually tapers towards the apex. The branches
arise in acropetal succession, i.e., oldest at the base and youngest
at the apex. The tree appears cone-shaped. e.g., Casuarina,
Eucalyptus, etc.

(d) Decurrent or Deliquescent : The apical bud of main (A) (B) (C)
stem is weak as compared to the buds of lateral branches. Thus, the
lateral branches are prominent and spreading. The main stem grows Fig : Forms of trees : (A) Caudex of a palm
upto a certain height after which it gives several branches. These (B) Excurrent of Polyalthia
branches dominate by giving the branches of several orders. The (C) Deliquescent of Ficus
whole tree looks like dome-shaped. e.g., Banyan (Ficus bengalensis).

(iii) Weak stems : They are thin, soft and delicate which are unable to remains upright without any external
support. They are of two types : upright weak stems and prostrate weak stems.

(a) Upright weak stem

• Twiners : The stems are long, slender, flexible and very sensitive. They twin or coil around an upright
support on coming in its contact due to a special type of growth movement called nutation. They may coil the
support to the right (anticlockwise from the top or sinistrorse) e.g., Convolvulus sp., Ipomoea quamoclit Clitoria
ternatea, etc. or to the left (clockwise or dextrorse), e.g. Lablab.

• Climbers : The stem is weak and unable to coil around a support. They usually climb up the support
with the help of some clasping or clinging structure. They are of four types :

(i) Tendril climbers : Tendrils are thread like structure which help in climbing the plants. They may be
modified stem (e.g., Vitis), stem branches (e.g., Passiflora) and inflorescence (e.g., Antigonon).

(ii) Root climbers : Adventitious roots arise from the nodes and penetrate into the upright support so that
the climber climbs up,e.g., Betel vine (Piper betel), Tecoma, Ivy, etc.

(iii) Scramblers or Hook climbers : These weak stemmed plants slowly grow over other bushes and rest
there. They attain this position with the help of curved prickles (e.g., Rose), curved hooks on flowering peduncle (e.g.,
Artabotrys), prickles on stem (e.g., Lantana), spines (e.g., Climbing Asparagus) or spinous stipules (e.g., Zizyphus).

(iv) Lianas : These are woody perennial climbers found in deep forests. At first, they are just like ordinary twiners
but once they reach to the top and get sunlight, become woody. e.g., Tinospora, Ficus, Bauhinia, Bignonia, etc.

(b) Prostrate weak stem

• Trailers : The stem creep on the ground but roots do not arise at the nodes. They are of three types :

(i) Procumbent : The stem creeps on the ground totally e.g., Tribulus, Bassela, Evolvulus.

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(ii) Decumbent : Branches, after growing horizontally for some length, grow vertically upwards, e.g.,
Portulaca, Tridax, Lindenbergia, etc.

(iii) Diffuse : Branches grow profusely in all directions, e.g., Boerhaavia.

• Creepers : These weak-stemmed plants grow prostrate and develop adventitious roots from their nodes.
Creepers are of three kinds – runners, stolons and offsets.

(i) Runners : This prostrate aerial stem has a long internode and creeps horizontally. Axillary buds arise from
nodes to form aerial shoots and roots. Several small (daughter) plants are thus linked by runner which may break
off later. e.g., Cynodon (doob grass) and Oxalis.

(ii) Stolons : They are special kinds of runners which initially grow upwards like ordinary branches and then
arch down to develop new daughter plants on coming in contact with the soil. e.g., Strawberry (Fragaria vesica),
Peppermint (Mentha piperita), Jasminum (Jasmine).

(iii) Offsets : They are weak, elongated, horizontal branch of one internode that arises in the axil of a leaf. At
the tip, it produces cluster of leaves above and tuft of roots below. The offset may break off from the parent plant
and act as individual plants. They are found usually in aquatic plants and rarely is terrestrial plants. They are helpful
for vegetative propagation. e.g., Eichhornia (water hyacinth), Agave, Pistia.

Modification of stem.

(1) Underground stem : In many plants the stems remain underground. There are many advantages for the
underground stems.

(i) They can store plenty of food material.

(ii) The underground stems are well protected from herbivorous animals.

(iii) They can live for longer time (perennation).

(iv) The underground stems can carryout vegetative propagation very easily.

The underground stems lack green colour because of their geophillous nature. They can be identified as stems
because of the presence of nodes, internodes, scale leaves, buds and branches. Based on the type of growth
(transverse/vertical/oblique) and the part that stores food (main stem/ branch/ leaf base), the underground stems are
classified into several types :

Underground stem modification

Sucker Rhizome Corm Tuber Bulb
Root stock Tunicated
Straggling Scaly

(i) Sucker : This is a sub aerial branch that arises from the main stem. Initially it grows horizontally below the

soil surface and later grows obliquely upward. They are shorter and stouter than the runners. e.g., Mentha arvensis

(mint vern. Podina) and Chrysanthemum.

(ii) Rhizome : The rhizome is a thickened, underground dorsiventral stem that grows horizontally at particular
depth within the soil. The rhizome is brown in colour and shows cymose branching. It can be distinguished from the
modified root by the presence of nodes, internodes, terminal bud, axillary bud and scale leaves. The terminal bud
develops aerial shoot that bears inflorescence. Adventitious roots develop on the ventral surface of the rhizome. The
rhizomes are perennial and vegetatively propagating structures. It is of following types :

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(a) Rootstock : They are upright or oblique with their tips reaching the soil surface. e.g., Alocasia indica and Banana.

(b) Straggling : They are horizontal in position and generally branched (Sympodial or Monopodial), e.g.,
Nelumbo nucifera (Lotus), Zingiber officinale (Ginger), Curcuma domestica (Turmeric), Saccharum etc.

(iii) Corm : The corm is an underground modification of main stem. It grows vertically at particularly depth in
the soil. The corm stores food materials and becomes tuberous. It is non green in colour and conical, cylindrical or
flattened in shape. The corm bears scale leaves at each node. In the axils of these scale leaves axillary buds arise which
grow into daughter corms. The terminal bud of the corm is large. It grows into aerial shoot and bears leaves and
flowers. Adventitious roots normally develop from the base or all over the body of the corm. With the help of some
special adventitious roots called the contractile roots or pull roots, the corm remains constantly at a particular depth.
The corm propagates vegetatively by daughter corms. e.g., Amorphophallus, Colocasia and Crocus (Saffron).

Terminal bud Axillary bud

Scale leaves

Scale leaves

(A) (B) (C)

Fig : Corms : (A) Colocasia, (B) Crocus (saffron) (C) Amorphophallus

(iv) Tuber : Stem tuber is the tuberous tip of an underground branch. It occurs beneath the soil at any depth.
The axillary branches (stolons) that are produced near the soil surface grow into the soil and their tip become
swollen due to accumulation of starch and proteins e.g., Solanum tuberosum (potato). In potato, the stem nature is
evident by the presence of ‘eyes’ on its brownish corky surface. Each eye is a pit like structure and represents the
node. At the rim of the eye, scale leaf scar is seen. Axillary bud is situated in the pit of the eye. The stem tubers are
differentiated from the tuberous roots by the presence of vegetatively propagating eyes.

(v) Bulb : A bulb is a specialized underground stem bears roots on it’s lower side and rosette of fleshy leaf
bases or fleshy scales on the upper side. In a bulb, the stem is reduced and becomes discoid. On the lower side of
the disc adventitious roots develop in clusters. The upper side of the disc shows compactly arranged fleshy leaf
bases or scale leaves so as to form an underground bulb. The leaf bases or scales become fleshy due to
accumulation of food (carbohydrates) and water. The terminal bud grows into inflorescence or aerial shoot (scape),
while some of the axillary buds develop into daughter bulbs. Bulbs are of two types, tunicated bulb and scaly bulb.

(a) Tunicated bulb : In tunicated bulb, the fleshy leaf bases are arranged in a concentric manner. The entire
bulb is covered by peripheral dry membranous leaf bases called tunics, hence called the tunicated bulb. e.g.,
Allium cepa (Onion), Narcissus and Tulip. Compound tunicated bulbs as in Allium sativum (garlic).

(b) Scaly or Imbricated bulb : In scaly bulb, the fleshy scale leaves are arranged loosely overlapping one
another. Such bulbs are not covered by any tunics, hence called naked bulbs or scaly bulbs. e.g., Lily.

(2) Aerial stem : The aerial stems are exposed to different environmental conditions. Hence they show many
modifications. The vegetative and floral buds of many plants instead of growing into branches and flowers, undergo
metamorphosis to form new structure.

Aerial stem modification

Tendrils Thorns Phylloclades Cladodes Thalamus

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2. Extra-axillary
3. Apical-bud tendril
4. Floral bud tendril

Morphology of Flowering Plants Part 1

(i) Tendrils : The tendrils are thin, wiry, leafless and spirally coiled branches. The terminal part of a tendril is
sensitive. It holds the support by coiling round it. The tendrils help the weak stems to climb the support. In some
weak stemmed plants, the axillary bud or terminal bud may modify to form tendrils which are specially called stem
tendrils. Stem tendrils are following four types :

(a) Axillary : e.g., Passiflora.

(b) Extra-axillary : e.g., Luffa (vern. Ghiatori), Cucurbita (vern. Kaddoo), Lagenaria (vern. Lauki).

(c) Apical bud tendrils : e.g., Grape Vine (Vitis vinifera).

(d) Floral bud or Inflorescence tendrils : e.g., Antigonon.

(ii) Stem thorns : The axillary buds of some plants become arrested and get modified into stiff, sharp and
pointed structures, called thorns. They are deep seated structures having vascular connections with stem. Besides
reducing transpiration, they protect the plant from browsing animals. e.g., Citrus, Duranta, Bougainvillea,
Pomegranate, Flacourtia, Aegle marmelos etc.

(iii) Phylloclades (Cladophyll) : The phylloclade is special modified photosynthetic stem present mostly in
xerophytes. It is green, flattened or cylindrical structure which has distinct nodes and internodes. Xerophytes show
many adaptations to check the rate of transpiration. Reduction of leaf size, early leaf fall, formation of scale leaves,
spines, thorns, thick cuticle, presence of fewer stomata are some of the xerophytic characters. In such cases, the
stems become flattened to carryout photosynthesis. These modified stems are called phylloclades or cladophylls.
Usually the phylloclades retain water in the form of mucilage. e.g., Opuntia, Casuarina, Cocoloba and Ruscus.

In Opuntia, the leaves are modified into spines and the stems becomes fleshy leaf like phylloclade. In Casuarina
the leaves are modified into scales. The phylloclade in Ruscus is leaf like and bear flowers. In Cocoloba, after the
modification of leaves into scales the stem becomes ribbon like phylloclade with distinct nodes and internodes.

(iv) Cladodes : These are modifications of stem and branches of limited growth. It has one internode only.
Each cladode is green, flat or cylindrical, leaf like structure which performs photosynthesis. In Asparagus, the leaves
are reduced to curved spines. In Ruscus aculeatus, the leaf like cladode are borne in the axils of scale leaves.

(v) Thalamus : Thalamus of a flower is a modified stem apex. The other floral parts (sepals, petals, stamens
and carpels) are born on the thalamus. It may be convex (Ranunculus), concave (Lathyrus) or flask shaped (Rosa).

Stem branching.

In angiosperms, always the branches are produced by the growth axillary buds or lateral buds. This type of
branching is known as lateral branching. The lateral branching is classified into two kinds racemose and cymose.

(1) Racemose branching : In this type of branching, the terminal (or apical) bud of the main stem grows
indefinitely and the axillary buds grow out into lateral branches in acropetal succession.

This type branching is also called monopodial branching. Due to monopodial branching the shoot system of
plant appears conical e.g., Eucalyptus, Polyalthia (Ashoka tree).

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(2) Cymose branching : In cymose branching the terminal bud is active for a short period and becomes
modified into some permanent structure like tendrils, thorns of flowers. Due to the terminal bud modification the
growth of the main stem is definite. Further growth in the plant is carried by one or more axillary buds. Cymose
branching may be of three types :

(i) Uniparous or Monochasial type : In uniparous type of branching only one lateral branch is produced at
each time below the modified terminal bud. Here the successive lateral
branches that are formed unite to form a stem. Such a stem is called false
axis or sympodium. The uniparous branching is of two kinds, helicoid
and scorpoid.

(a) Helicoid branching : If the successive lateral branches (A) (B)
develop on one side it is called helicoid branching. e.g., Saraca, Canna
and Terminalia. Fig : Types of uniparous branching
(A) Halicoid type branching in Terminalia
(b) Scorpioid branching : If the successive lateral branches (B) Scorpioid type branching in Carissa
develop on either side alternately, it is called scorpioid branching, e.g.,
Cissus, Gossypium and Carissa.

(ii) Biparous or Dichasial type : When the activity of terminal bud stops, further growth of plant takes
place by two lateral branches, e.g., Viscum (Mistletoe), Silene, Stellaria, Mirabilis jalapa (Four O’ clock), Dianthus
(Pink), Carissa carandas (Karonda), etc.

(iii) Multiparous or Polychasial type : When the activity of terminal bud stops, further growth of plant
takes place by a whorl of three or more axillary branches. The axis is said to be multipodial, e.g. Euphorbia tirucalli,
Croton, Nerium odoratum (Oleander).

Buds.

A bud is a compact underdeveloped young shoot consisting of a shoot apex, compressed axis and a number
of closely overlapping primordial leaves arching over the growing apex. Sometimes a bud may occur as a mass of
undifferentiated meristematic tissues not showing the leaf primordia. Buds which develop in to flower are called
floral buds. In many plants buds take rest during unfavorable conditions. In mango, buds take residuring summer.
So they are called summer resting buds. In Cinnamomum, buds take rest during winter. Such buds are described as
winter resting buds. The largest vegetative bud in the plant kingdom is cabbage.

(1) Types of buds : The buds are classified into different kinds on the basis of their nature and position in the
plants.

Buds

Based on nature Based on position

Vegetative Floral Mixed

Normal Adventitious Bulbils
(Specialised buds)
Apical Lateral Epiphyllous Radical Cauline

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(i) Nature of buds : According to nature or structure of buds, they are following types :

(a) Vegetative buds : These buds grow to form only leafy shoots.

(b) Floral buds : These buds grow to form flowers.

(c) Mixed buds : They produce both vegetative and floral branches.

(ii) Position of buds : According to position of buds, they are following types :

(a) Normal buds : These buds are borne on stems either terminally or laterally. Since they are borne in
normal positions, they are called normal buds :

• Apical buds : They are borne at the apex of the main stem or a branch. They are also called terminal
buds. Cabbage is a large apical bud.

• Lateral buds : The buds, which are borne in any other place except at the apices of main stem and its
branches, are called lateral buds. They are of three types :

• Axillary buds : They occur in the axils of leaves, e.g., Sun-flower, Rose etc.

• Accessory buds : Additional buds occurring in the axil of a single leaf either on the side or above the
axillary bud e.g., Cucurbita, Brinjal, Chilly, Bougainvillea, etc.

• Extra-axillary buds : These buds develop on the node but outside the leaf base e.g., Solanum nigrum, etc.

(b) Adventitious buds : When a bud grows from a position other than normal, it is called adventitious bud.
These may be of the following types :

• Epiphyllous buds : When the buds arise on the leaves they are called epiphyllous buds, e.g.,
Bryophyllum. These buds usually develop at the angles of the crenate margins and help in vegetative propagation.

• Cauline buds : These buds arise on the stem or branches generally at the cut end or pruned end, e.g.,
Rose and Duranta.

• Radical buds : When the buds arise on the roots, they are called radical buds, e.g., Sweet potato, Coffee, etc.

(c) Bulbils or Specialised buds : Modification of whole buds into swollen structures due to storage of food
materials are called bulbils. When these bulbils detach from parent plant and fall on ground, they germinate into
new plants and serve as means of vegetative propagation. e.g., In Lilium bulbiferum and Dioscorea bulbifera, the
bulbils develop in axil of leaves; in Agave, floral buds of inflorescence transform into bulbils; In Oxalis, they develop
just above the swollen roots.

The leaf.

The leaf is a green, flat, thin, expanded lateral appendage of stem which is borne at a node and bears a bud in
its axil. It is exogenous in origin and develops from the leaf primordium of shoot apex. The green colour of leaf is
due to presence of the photosynthetic pigment – chlorophyll which helps plants to synthesize organic food. The

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green photosynthetic leaves of a plant are collectively called foliage. They are borne on stem in acropetal
succession.

(1) Characteristics of leaf
(i) The leaf is a lateral dissimilar appendage of the stem.
(ii) A leaf is always borne at the node of stem.
(iii) Generally there is always an axillary bud in the axil of a leaf.

(iv) It is exogenous in origin and develops from the swollen leaf primordium of the growing apex.

(v) The growth of leaf is limited.

(vi) The leaves do not possess any apical bud or a regular growing point.

(vii) A leaf has three main parts – Leaf base, petiole and leaf lamina. In addition, it may possess two lateral
outgrowths of the leaf base, called stipules.

(viii) The leaf lamina is traversed by prominent vascular strands, called veins.

(2) Parts of a typical leaf : The leaf consists of three parts namely, leaf base (usually provided with a pair of
stipules), petiole and leaf blade or lamina.

(i) Leaf base (Hypopodium) : Leaf base is the lower most part of the leaf meant for attachment. It acts as a
leaf cushion. In most of the plants it is indistinct. Some times leaf base shows different variations as follows :

(a) Pulvinate leaf base : In members of leguminosae the leaf is swollen. Such swollen leaf bases are called
pulvinate leaf bases as seen in mango leaves. It helps in seismonastic movements (e.g., Mimosa pudica) and
nyctinastic movements (e.g., Enterobium, Arachis, Bean).

(b) Sheathing leaf base : In grasses and many monocots, the leaf base is broad and surrounds the stem as
an envelope, such a leafbase is called sheathing leaf base. e.g., Sorghum, Wheat and Palms. In grasses (Sorghum,
Wheat etc.) the sheathing leaf base protects the intercalary meristem.

(c) Modified leaf base : The leaf bases in few plants perform accessory functions and show modifications. In
Allium cepa (Onion), the leaf bases store food materials and become fleshy. They are arranged concentrically to
form a tunicated bulb. In Platanus and Robenia, the leaf bases protect the axillary buds and grow around them to
form cup like structures.

(d) Stipule : The stipules are the small lateral appendages present on either side of the leaf base. They protect
the young leaf or leaf primordia. Leaves with stipules are called stipulate and those without them are called
exstipulate. The stipules are commonly found in dicotyledons. In some grasses (Monocots) an additional
outgrowth is present between leaf base and lamina. It is called ligule. The leaves having ligules are called ligulate.
Sometimes, small stipule like outgrowths are found at the base of leaflets of a compound leaf. They are called
stipules.

• Types of stipules : Depending upon the structure and position various kinds of stipules are recognized.

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• Free lateral stipules : A pair of freely arranged stipules present on either side of the leaf base are called
free lateral stipules, e.g., Hibiscus and Cotton.

• Adnate stipules : The two stipules that fuse with the leaf base or petiole on either side are called adnate
stipules, e.g., Arachis and Rose.

• Inter petiolar stipules : Stipules present in between the petioles of opposite leaves, e.g., Ixora and
Hamelia.

• Axillary stipules : Stipules present in the axil of a leaf are called axillary stipule. These are also called
intrapetiolar stipule, e.g., Tabernamontana and Gardenia.

• Ochraceous stipules : Membranous tubular stipules that ensheath the axillary bud and a part of
internode is called ochraceous stipule. It is formed by the union of two stipules, e.g., Polygonum and Rumex.

• Hairy stipules : These are hair like stipules which are dry in nature, e.g., Anacampsora.

• Modification of stipule : To carryout different functions, stipules of some plants undergo modifications.
They are classified as follows :

• Foliaceous : Green, expanded, leaf like stipules are called foliaceous stipules. They carryout
photosynthesis, hence called assimilatory stipules, e.g., Pisum sativum and Lathyrus.

• Spinous : In some plants the stipules are modified into hard, pointed defensive organs called spines, e.g.,
Acacia arabica, Prosopis juliflora and Zizyphus.

• Convolute or Bud scales : Scales which protect the buds are called bud scales. Sometimes they are the
modified to stipules. The bud scales fall off as the buds open, e.g., Artocarpus and Ficus.

(ii) Petiole (Mesopodium) : A petiole or leaf stalk is a cylindrical or sub cylindrical structure of a leaf which
joins the lamina to the base. It raises the lamina above the level of stem so as to provide it with sufficient light
exposure. A leaf with a petiole is called petiolate and the one without it is called sessile.

(a) Modification of petiole

• Winged petiole : Green, flattened petioles may be called winged petioles, e.g., Citrus and Dionaea.

• Tendrillar petiole : In few plants the petioles are modified into tendrils and helps the plant in climbing.
e.g., Clematis and Tropaeolum.

• Leaf like petiole (Phyllode) : A modified petiole which is flat, green Apex
and lamina like is called phyllode. It is a photosynthetic organ. e.g., Acacia auriculae
formis. Margin
Veins
• Swollen or Spongy petiole : Sometimes the petiole becomes swollen Lamina
and spongy due to the development of aerenchyma. The type of petioles encloses (epipodium)
much air and helps the plant to float. It is a hydrophytic adaptation e.g., Trapa Midrib
bispinosa and Eichhornia.
Petiole Axillary bud
(Mesopodium)
Stipule
Leaf base Stem
(Hypopodium)

Fig : Part of a typical leaf

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• Spinous petiole : In few plants, the leaf blades fall off and the petioles become hard and spinous e.g.,
Quisqualis (Rangoon creeper).

(iii) Lamina (Epipodium) : The green expanded portion of the leaf is called the lamina. It performs vital
functions like photosynthesis and transpiration. The nature of lamina depends upon the species and age of the leaf.
A leaf lamina shows variations in different aspects like shape, margin, apex, texture and venation.

(a) Shape of lamina : The shape of the lamina is the description of its form. It varies in different plants as
follows.

(1) Acicular type (2) Linear type
Needle shaped leaves. Long and slightly broader leaves.

Pinus Grass

(3) Lanceolate type (4) Orbicular type
Lance shaped leaves. More or less circular leaves.

Nerium Lotus
Vinca
(5) Elliptical type (6) Ovate type
Leaves are like an ellipse. Egg shaped (oval) leaves.

(7) Spathulate type Hibscus
Spoon like leaves.
(8) Oblique type
Leaf lamina is with unequal half.

Euphorbia Margosa

(9) Oblong type (10) Reniform type
Rectangular leaves. Kidney shaped leaves.

Banana Hydrocotyle
Betel vine
(11) Cordate type (12) Saggitate type
Heart shaped (with a
deep notch at the Leaves shaped like an
base) leaves. arrow head.

(13) Hastate type Sagittaria
Leaves like saggitate
(14) Lyrate type

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but the two basal lobes Leaves shaped like a lyre.
are directed outwards.

(15) Centric type (16) Cuneate type
Hollow and cylindrical leaves. Wedge shaped leaves.

Onion Pistia

(b) Margin of lamina : The margin of the lamina may be of different types as given.

Entire Serrate Repand Dentate Crenate Spiny
Leaves have Leaves have Leaves have
Leaves with saw like margin. wavy margin. Leaves have Leaves have spiny margin.
smooth margin. large pointed round teeth
teeth like margin. margin.

Mango Hibiscus Polyalthia Aloe Bryophllum Argemone

(c) Apex of lamina : The apex of the leaf lamina shows variations in different plants.

(1) Acute (2) Acuminate

The apex is narrow and The apex is draw out into a
pointed. e.g., Mango. long tapering tail. e.g., Ficus
religiosa.

(3) Obtuse (4) Mucronate
The apex is rounded. e.g., Banyan.
Round apex wit sharp
pointed tip. e.g., Vinca.

(5) Cuspidate (6) Tendrillar
The apex is spinous. e.g., Date palm.
The apex form a tendril.
e.g., Gloriosa.

(7) Cirrhose (8) Truncate
The mucronate like apex The shape is abruptly cut

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ends with fine thread like across. e.g., Paris
structure. e.g., Banana. polyphylla.

(9) Retuse (10) Emarginate
The obtuse apex is The obtuse apex is
slightly notched. deeply notched. e.g.,
e.g., Pistia. Baukinia.

(d) Surface of lamina : The surface of the lamina may be of many kinds.

• Glabrous : Smooth and without hair. e.g,. Mangifera indica.
• Glaucus : Covered by waxy coating with white tinge. e.g., Calotropis.

• Scabrous : Rough surface. e.g., Ficus.

• Viscose : Sticky surface. e.g., Cleome.
• Pubescent : Covered with soft and wooly hair. e.g., Tomato.

• Pilose : Covered with long distinct scattered hair. e.g., Grewia pilosa.

• Hispid : Covered with long rigid hair. e.g., Cucurbita.
• Spinose : Covered with small spines. e.g., Solanum xanthocarpum.
(e) Texture of lamina : The texture of lamina also varies in different species.

• Herbaceous : When the lamina is thin and soft.
• Coriaceous : When the lamina is leathery.

• Succulent : When the lamina is thick, soft and juicy.

• Hygrophytic : When the lamina is very thin, membranous and spongy.
(3) Types of leaves : On the basis of shape of lamina, the leaves are classified into two types, namely, simple
leaf and compound leaf.

(i) Simple leaves : The leaf having single undivided lamina is called the simple leaf. The simple leaf may be
entire (e.g., Mango and Hibiscus rosa sinensis) or lobed. The lobes of a simple leaf may be entire pinnately
arranged (e.g., Brassica) or palmately arranged (e.g., Gossypium, Passiflora and Ricinus).

(ii) Compound leaves : A compound leaf is one in which the lamina or the leaf blade is completely divided
into many segments or units called leaflets or pinnae. When pinnae of leaflets attached in various ways to the
portion of leaf axis known as the rachis. The compound leaves may be of two types, namely, pinnate compound
leaves and palmately compound leaves.

(a) Pinnate compound leaves : It is the most familiar and widesperead type of compound leaf in which the
rachis is elongated and bears two rows of simple or divided leaflets. The leaflets may be arranged alternately or in
pairs along with the rachis. It is of following types :

• Unipinnate compound leaf : Here the primary rachis is unbranched and bear leaflets on either side.
Unipinnate leaves are of two types :

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• Paripinnate : The unipinnate leaf with even number of leaflets. They are borne in pairs. e.g.,
Tamarindus indica (Imli), Cassia etc.

• Imparipinnate : The unipinnate leaf with odd number of leaflets. The rachis is terminated by single
unpaired leaflet. e.g., Neem, Rose, Murraya.

• Bipinnate compound leaf : In this type, the primary rachis is divided once and produce secondary and
tertiary rachis. The leaflets develop on the secondary rachis. e.g., Delonix and Acacia, Mimosa pudica, Albizzia.

• Tripinnate compound leaf : In this type the primary rachis divides twice and produces secondary and
tertiary rachii. The leaflets develops on the tertiary rachii. e.g., Moringa (Soanjana) and Millingonia.

• Decompound leaf : Here the primary rachis divides many times without any definite order. The lamina
is dissected into many units. e.g., Coriandrum.

(b) Palmate compound leaf : In a palmately compound leaf, the leaflets are arranged at the tip of the
petiole. According to the number of leaflets present at the tip of the petiole. These leaves are following types :

• Unifoliate : In this case, a palmately compound leaf is reduced to a single terminal leaflet. The single
leaflet is articulated to the top of petiole, e.g., Citrus (Khatta), Lemon, etc.

• Bifoliate : This type of leaf has only two leaflets attached side by side at the terminal end of petiole, e.g.,
Balanites roxburghii, Hardwickia binata, etc.

• Trifoliate : This type of leaf has three terminal leaflets, Aegle marmelos (Wood apple, vern. Bael), Oxalis
corniculata, Trifollium (Clover), etc. These leaves differ from trifoliate imparipinnate (e.g., Lablab) in having all the
three leaflets attached at the tip of petiole.

• Quadrifoliate : This leaf has four leaflets attached to the tip of petiole. e.g., Paris quadrifolia, Marsilea.

• Multifoliate : A palmately compound leaf having five or more terminal leaflets, arranged as fingers of
the palm, e.g., Bombax malabarica, Cleome viscosa, Gynandropsis pentaphylla, etc.

(4) Phyllotaxy (Phyllotaxis) : The leaves may be stem borne (cauline), branch borne (ramal) or may appear
to be root borne (radical). The arrangement of leaves on the stem is called phyllotaxy (Gk. Phyllon = leaf; taxis =
arrangement). It is of three types :

(i) Alternate or Spiral : When only one leaf is found at each node. The leaves present at successive nodes
alternate with each other. The arrangement is said to be alternate or spiral. The leaves are commonly arranged
spirally around the stem. Each spiral is called the genetic spiral. The angular divergence (angular distance) between
any two concecutive leaves is always constant. In spiral phyllotaxy, the leaves are arranged on the stem in regular
vertical row. Such rows are called orthostichies. In practice the angular divergence is determined in the following
manner :

Angular divergence = No.of circles of a circle i.e. 360°
Orthostichies

A phyllotaxy is written by taking the number of spirals (circles) as numerator and the number of leaves as
denominator. Based on the number of orthostichies seen on the stem, the spiral phyllotaxy may be described as
given under.

(a) Distichous or 1/2 Phyllotaxy : Where the angular divergence is 1/2 of 360° i.e., 180°. e.g., Ravenella.

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(b) Tristichous or 1/3 Phyllotaxy : Where the angular divergence is 1/3 of 360° i.e., 120°. e.g., Moss,
Cyperus rotundus.

(c) Pentastichous or 2/5 Phyllotaxy : Where the angular divergence is 2/5 of 360° i.e., 140°. e.g., China rose.

(d) Octastichous or 3/8 Phyllotaxy : Where the angular divergence is 3/8 of 360° i.e., 135°. e.g., Carica papaya.

In these types, if one adds up two preceeding numerators and denominators, a series is formed called
Schimper-Brown Series.

e.g., 1 , 1 , 1 + 1 = 2 , 1 + 2 = 3 , 2 + 3 = 5 , and so on.
2 3 2 + 3 5 3 + 5 8 5 + 8 13

(ii) Opposite : When two leaves are present at node opposite to each other the type of phyllotaxy is called
opposite. It is of two type :

(a) Opposite superposed : All the pair of leaves of a branch arise in the same plane so that only two vertical
rows of leaves are formed. e.g., Jamun, Guava, etc.

(b) Opposite decussate : A pair of leaves at one node stands at right angle to the next upper or lower pair
so that four vertical rows are formed on the stem. e.g., Calotropis, Zinnia, Tulsi, Quisqualis.

(iii) Whorled : If more than two leaves are present at a node as whorl, it is called whorled phyllotaxy. It is also
called cyclic or verticellate phyllotaxy. e.g., Nerium, Hydrilla and Alstoni scholaris.

(iv) Leaf mosaic : This is a special type of arrangement of leaves. Older leaves present at the lower nodes of
the stem possess longer petioles with bigger lamina and the young leaves of upper nodes bear shorter petioles with
smaller lamina. The smaller young leaves occupy the space present between the bigger ones. e.g., Begonia,
Acalypha and Sycamore.

(5) Vernation : Arrangement of leaves in bud condition is known as vernation imbricate (irregular
overlapping), contorted (twisted, regular overlapping of margins), induplicate (margin bent inwardly), equitant
(conduplicate in two series, one overlapping the other completely), half equitant, supervolute (convolute leaves, one
rolled over other).

(6) Heterophylly : It is the occurrence of more than one type of leaves on the same plant. Heterophylly is of
four types :

(i) Adaptive heterophylly : Submerged leaves are different from floating and emerged leaves of the same
plant due to different adaptations. e.g., Limnophila heterophylla, Sagittaria, Ranunculus aquatilis. The emerged
leaves are broad and fully expanded while the submerged leaves are narrow, ribbon shaped, linear or highly
dissected.

(ii) Environmental heterophylly : The heterophylly is due to change in environment including soil,
temperature, humidity and air currents.

(iii) Developmental heterophylly : Young leaves are different from mature leaves, e.g., Eucalyptus.

(iv) Habitual heterophylly : Leaves of different shape and incisions occur at the same time, e.g., Jack fruit
tree (Artocarpus heterophyllus), Ficus heterophylla, Hemiphragma heterophyllum, Broussonetia papyrifera. In
Hemiphragma, the main stem bears ovate and entire leaves while branches possess acicular leaves.

(7) Modification of leaves : Some important leaf modification are as follows :

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(i) Leaf tendrils : In many weak stemmed plants, the leaves are modified into slender wiry and coiled
structures called leaf tendrils. The tendril may be formed by entire leaf or a part of the leaf.

• Entire leaf modified into tendril, e.g., Lathyrus aphaca (Wild pea).

• Terminal leaflets modified into tendril, e.g., Pisum sativum (Pea), Lathyrus odoratus (Sweet pea), Narvella.

• Leaf tip modified into tendril, e.g., Gloriosa.

• Petiole modified in to tendril, e.g., Clematis.

• Stipule modified into tendril, e.g., Smilax.

• Midrib modified into tendril, e.g., Nepenthes.

(ii) Spines : A pointed structure formed by the modification of entire leaf or part of a leaf is called a spine.
Different part of a leaf or entire leaf may be modified in to spines. e.g., In Opuntia leaves of axillary branches are
modified into spines. In Berberis entire leaf modified into three spines. In Phoenix leaf tip modified into spine. In
Citrus first leaf of axillary branch modified in to spine. In Argimone leaf margin modified into spines. In Perkinsonia,
Acacia and Zizyphus stipules modified into spines.

(iii) Scale leaves : In many xerophytes, the foliage leaves are reduced to scale leaves. They are thin,
membranous, dry, small, sessile, colourless structure. e.g., Casuarina, Orobanche and Balanophora.

(iv) Phyllode : It is a green, expanded structure formed by the modification of petiole or rachis of leaf. Many
xerophytes reduce the size of their leaves to minimize water loss. Such plant develop phyllodes to carry out
photosynthesis e.g., Acacia, Melanoxylon and Parkinsonia.

(v) Storage leaves : Leaves become fleshy due to storage of water or food materials. Such leaves are called
storage leaves. They are usually found in succulent plants. In plants like Aloe, Kalanchoe and Peperomia.

(vi) Reproductive leaves : In some plants the vegetative propagation is carried out by the production of
epiphyllous buds on leaves. Such leaves are called reproductive leaves. The epiphyllous buds when come in contact
with soil develop into new plants.

(vii) Absorbing leaves : In some rootless, aquatic plants, the submerged leaves are modified into root like
structure to absorb water and mineral salts. Such modified leaves are called absorbing leaves. e.g., Utricularia.

(viii) Floral leaves : Floral parts such as sepals, petals, stamens and carpels are modified leaves. Sepals and
petals are leafly stamens are considered pollen bearing microsporophylls and carpels are ovule bearing
megasporophylls.

(ix) Cotyledons : The mature embryo shows either one (monocotyledons) or two cotyledons, (dicotyledons).
Cuscuta a parasite is included in dicotyledon. However it has no cotyledon and many cotyledons, as in
gymnosperms. These cotyledons are considered as embryonic leaves which are the first leaves of a shoot system.

(x) Trap leaves : The trap leaves are also called insectivorous leaves or carnivorous leaves. Plants having trap
leaves usually grow in nitrogen-deficient soils (boggy soils). They have poorly developed root system. These plants
get their nitrogenous requirement by capturing the insects. To attract, capture, kill and digest the insects, the leaves
are modified into trap leaves.

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Venation.

The arrangement of veins in the lamina of a leaf is called venation. The veins are the hard structures
consisting of xylem and pholem. The veins give mechanical strength and shape to the lamina. Also they are
responsible for conduction of water, minerals and organic food materials. Angiosperms exhibit two types of
venation.

(1) Reticulate venation : In this type, the lateral veins divide and redivide to form many veinlets. These
veinlets are arranged in a net like fashion or reticulum. Reticulate venation is the characteristic feature of
dicotyledons. But exceptionally some monocotyledons also show reticulate venation. e.g., Smilax, Alocasia and
Dioscorea. Reticulate venation is of two types :

(i) Unicostate or Pinnate venation : This type of venation is characterized by the presence of a single
strong midrib that extends upto the apex of lamina. The midrib produce lateral veins on either side which divide
repeatedly. The ultimate branches unite to form a network. This type of venation is also called unicostate reticulate
venation, because of the presence of a single prominent midrib. e.g., Ficus and Mangifera.

(ii) Multicostate or Palmate venation : Here more than one prominent veins start from the base of the lamina
and proceed upwards. The lateral veinlets, arising from main veins, form network. Multicostate venation is of two types :

(a) Convergent : When the prominent veins converge towards the apex of lamina. e.g., Zizyphus and
Cinnamonum.

(b) Divergent : When the prominent veins spread out towards the margins. e.g., Papaya, Ricinus, Cucurbita etc.

(2) Parallel or Striate venation : In this type, veins and veinlets run parallel to each other. They do not form
any network or reticulum. Parallel venation is the characteristic feature of monocotyledons. Exceptionally few dicots
show parallel venation, e.g., Calophyllum and Eryngium. It is of two types :

(i) Unicostate or Pinnate venation : The leaf lamina possesses single prominent vein which gives rise to a
large number of lateral veins. All the lateral veins run parallel towards margin. e.g., Banana, Canna, Curcuma etc.

(ii) Multicostate or Palmate venation : The leaf lamina possesses several prominent veins which run
parallel to each other. It is of two types :

(a) Convergent : The prominent veins run parallel to each other and converge at the apex. e.g., Sugarcane,
Maize, Wheat, Bambooes and Grasses.

(b) Divergent : All the prominent veins of leaf lamina spread out towards the margin. e.g., Fan palm.

Flower.

It can be defined as modified dwarf shoot which is meant for sexual reproduction. It is characteristics feature of
angiosperm whease reproductive organs have been aggregated as flowers.

(1) Parts of a typical flower : It comprises a stalk called pedicel which arises in the axis of leaves called
bracts. Upon the pedicel there may be one to many small scaly structures called bracteoles. The terminal part of
the pedicel is the thalamus or torus. It is a modified and condensed axis of the flower. Modified leaves called floral
leaves or floral parts arises from the nodes of the thalamus as successive whorls. A typical flower of an angiosperm
consists of four types of floral parts namely calyx, corolla, androecium and gynoecium.

(i) Calyx : It is the outermost whorl composed of sepals.

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(ii) Corolla : It is composed of petals and is the second whorl.
(iii) Androecium : It is the third whorl composed of stamens.
(iv) Gyneocium : It is the innermost whorl and is also called pistil. It shows carpels.
(2) General description of a flower : The flowers are termed pedicellate if they possess stalks and sessile if
they lack them. The flower may be described as complete if it bears all the floral parts and incomplete, when one or
more floral parts are absent. Flowers are called bisexual if they bear both androecium and gynoecium. The
unisexual flowers have either androecium or gynoecium. The unisexual flowers may be male flowers or female
flowers. The male flower are also called staminate flowers as they have stamens only. The female flowers have only
the carpels and hence called pistillate flowers. Flowers with sterile sex organs are described as neutral flowers.
According to the distribution of male, female and bisexual flowers, various pattern are recognized.
(i) Monoecious : Presence of male and female flowers on the same plant, e.g., Acalypha, Cocos and Ricinus.
(ii) Dioecious : Presence of male and female flowers on different plants, namely, male plants and female
plants. e.g., Cycas, Carica papaya and Vallisneria.
(iii) Polygamous : Presence of unisexual and bisexual flowers on the same plant, e.g., Mangifera and Polygonum.
(3) Symmetry of flower : The number, shape, size and arrangement of floral organs in a flower determines
its symmetry. On the basis of symmetry flowers can be of the following types :
(i) Actinomorphic (Regular = Symmetrical) : Actinomorphic flowers can be divided (passing through
center) by any vertical plane in to two equal and similar halves. e.g., Mustard, Brinjal, Catharanthus roseus.
(ii) Zygomorphic (Monosymmetrical) : Zygomorphic flowers can be divide into two equal halves by only
one verticle division e.g., Pea, Larkspur, Ocimum.
(iii) Asymmetrical (Irregular) : Asymmetrical flowers can not be divided into two equal halves by any
vertical division. e.g., Canna, Orchids.

(A) (B) (C)

Fig : Symmetry of flowers
(A) Actinomorphic, (B) Zygomorphic, (C) Asymmetrical

(4) Arrangement of floral organs : On the basis of arrangement of floral organs, three types of flowers are
recognized. They are :

(i) Acyclic : Here the thalamus is conical or convex and the floral parts are spirally arranged, e.g., water lily
and Magnolia.

(ii) Cyclic : Here the floral organs are arranged in regular whorls at the nodes of the thalamus, e.g., Hibiscus
and Datura.

(iii) Hemicyclic (Spirocyclic) : Here some floral parts (sepals and petals) are arranged in regular whorls
and the remaining parts (stamens and carpels) are arranged spirally. e.g., Annona and Polyalthia.

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Number of floral parts in whorl is called the merosity. There are two kinds of flowers based on the merosity of
the flower. They are isomerous flowers and anisomerous flowers.

• If the number of sepals, petals, stamens and carpels of flower is equal, such flowers are called isomerous flowers.
Dimerous : Two floral parts in each whorl.

Trimerous : Three floral parts in each whorl.

Tetramerous : Four floral parts in each whorl.

Pentamerous : Five floral parts in each whorl.

• A flower with different number of floral parts in each whorl is called anisomerous flower. The sepals,
petals, stamens and carpels present at different whorls of a flower vary in their numbers. These are also called
heteromerous flowers.

(5) Detailed structure of flower : Angiospermic flowers exhibit many variations in their external
morphological characters. Detailed description of a flower helps in its proper identification.

(i) Bract : Bract (hypsophyll) is a small leaf like structure on the peduncle which produces a flower in its axil.
The floral buds are usually protected by the bracts. Flower with a bract is described as bracteate and the flower
without a bract is known as ebracteate. Bracteoles are small scale like structures present on the pedicel. Bracts are
modified into following structures :

(a) Foliaceous bract : Leaf like, expanded green bract is called the foliaceous bract, e.g., Pisum, Lathyrus,
Adathoda and Gynandropsis.

(b) Spathe : A large modified bract which encloses spadix inflorescence totally or partially. It may be leathery
or woody, e.g., Alocasia, Cocoa, Musa and Typhonium.

(c) Petaloid bract : Brightly coloured petal like bract is known as petaloid bract, e.g., Bougainvillea,
Poinsettia and Euphorbia.

(d) Involucre : One or two whorls of green bracts that protect young inflorescence is called involucre, e.g.,
Coriandrum, Tagetes and Heracleum.

(e) Epicalyx : Whorl of bracteoles present below the calyx or outside the calyx, e.g., Hibiscus rosa sinensis
and Malvaviscus arborcus.

(f) Scaly bracts : Reduced, membranous, scale like bracts seen in head inflorescence, e.g., florets in Tridax
and Helianthus.

(g) Glumes : The bracts found on the rachilla of spikelet are called glumes. They may be sterile glumes or
fertile glumes (lemma), e.g., Oryza sativa.

(ii) Thalamus : The terminal part of the pedicel is called thalamus or torus or receptacle. It is a condensed
axis of the flower from which all floral parts arise. Depending upon the position of gynoecium on the thalamus with
respect to other parts, flowers are of three kinds – hypogynous, perigynous and epigynous (See details in
Embryology Module-II).

In many flowers, the thalamus is condensed and the internodes are not seen clearly. But there are some
flowers with elongated, distinct floral internodes as mentioned below :

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(a) Anthophore : This is the first elongated internode between the calyx and corolla, e.g., Silene,
Pennsylvania and Lychnis.

(b) Androphore : It is the second elongated internode between corolla and
androecium, e.g., Gynandropsis.

(c) Gynophore : It is the third elongated internode between androecium and Gynophore
gynoecium e.g., Capparis and Gynandropsis.
Androphore

(d) Gynandrophore : It is an elongated stalk like part between non essential
and essential organs of the flower. It is equivalent to androphore, e.g., Passiflora.

(e) Carpophore : This is a stalk like connection present between two carpels.

It is formed due to expansion of the thalamus between the carpels, e.g., Fig : Androphore and
Coriandrum and Foeniculum. gynophore of

Gynandropsis

(iii) Perianth : The non essential organs, calyx and corolla are together called

perianth. The perianth protects the stamens and carpels. In angiospermic flowers, the perianth exists in different

forms.

(a) Achlamydeous : Perianth is absent and the flowers appear naked. Mostly the achlamydeous flowers
occur in cyathium inflorescence. e.g., Euphorbia, Poinsettia.

(b) Chlamydeous : Perianth is present and the flowers usually appear attractive. The chlamydeous flowers
are of two types. They are :

• Monochlamydeous flowers are with perianth in one whorl, e.g., Amaranthus and Ricinus.

• Dichlamydeous flowers are with perianth differentiated into calyx and corolla. They are arranged in two
different whorls. The dichlamydeous condition is of two types :

• Homochlamydeous : The two whorl or the perianth (calyx and corolla) are similar in all respects and
are not identified by different colours, e.g., Michelia.

• Heterochlamyoeous : The two whorls of the perianth are dissimilar in many respects. The outer whorl
consists of small, green sepals and the inner whorl with large variously coloured petals, e.g., Datura and Hibisus.
The term “tepals” is used to describe the perianth lobes which appear like petals, e.g., most of the monocots.

(iv) Calyx : It is the outermost whorl of the flower. It consist of sepals. Usually, the sepals are small and green.
They protect other floral organs when the flower is in bud condition. The calyx is described as polysepalous when
the sepals are free (e.g., Anona, Tomato) and gamosepalous when the sepals are united (e.g., Datura and Hibiscus).
If sepals are fused less than half of the length of calyx tube it is called as partite and if the fusion of sepals is very
little, just at the base of calyx tube, it is said to be connate. The sepals may be deciduous or persistent. Usually the
persistent calyx do not show any growth after fertilization. Such a calyx is termed as marcescent (e.g., Brinjal,
Chillis). Sometimes the persistent calyx shows continuous growth even after, fertilization. This type of calyx called
acrescent (e.g., Physalis and Shorea).

In some plants a whorl of green sepals like structure is present at the base of calyx called epicalyx. Epicalyx is
considered a whorl of the bracteoles and mostly found in the flowers of family Malvaceae (Althaea, Cotton). The
calyx may show number of modifications. They are :

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(a) Campanulate : Bell shaped, e.g., Althaea.
(b) Cupulate : Cup like, e.g., Gossypium.
(c) Urceolate : Urn shaped, e.g., Hyoscyamus.
(d) Infundibuliform : Funnel shaped, e.g., Atropa belladona.
(e) Tubular : Calyx tube like, e.g., Datura.
(f) Bilabiate : Calyx forms two lips, e.g., Ocimum.
(g) Spurred : One or two sepals forming a beak like structure, e.g., Larkspur.
(h) Pappus : Calyx are modified into hairs e.g., Sonchus, Tridax (Asteraceae).
(i) Spinous : When calyx forms spines, e.g., Trapa.
(j) Hooded : When sepals enlarged to form a hood over the flower, e.g., Aconitum.
(k) Petaloid : Enlarged and brightly coloured sepals, e.g., Clerodendron, Mussaenda, Sterculia, Caesalpinia
and Saraca.
(v) Corolla : It is the second whorl of the flower consisting of petals. Usually the petals are brightly coloured
and scented. They attract the insects which act as agents for pollination. The corolla may be polypetalous (with
free petals), gamopetalous (with united petals) or apetalous (without petals). The corolla may undergo
modifications or possess some special appendages.

• Sepaloid : Green or dull coloured sepal. e.g., Anona, Polyalthia and Artabotrys.
• Saccate : The corolla tube may form a pouch on one side. e.g., Antirrhinum.
• Spurred : Sometimes one or two petals or the entire corolla tube grow downwards forming a spur that
usually stores nectar. e.g., Aquilegia vulgaris.

• Corona : Special appendages of different kinds like scales, hairs develop from the corolla. Such
appendages are called corona. e.g., Passiflora, Oleander and Nerium.

Forms of corolla : Both polypetalous and gamopetalous corolla exhibit great variation in their forms. It is
following types :

(a) Polypetalous corolla : They are of following types :

• Cruciform : Four free clawed petals arranged in the form of a cross, e.g., Mustard and Radish.
• Rosaceous : Five free sessile petals withlobes spreading outwards, e.g., Rose, Hibiscus.
• Caryophyllaceous : Five free clawed petals with limbs at right angles to the claw, e.g., Dianthus.
• Papillionaceous : Five free unequal petal arranged in definite fashion. The posterior petal is largest and
is called standard vexillum. On either side of the standard, two lateral petals unite called wings are present. The
remaining two anterior petals to form a boat shaped structure called the keel. e.g., plants of papillionaceae.

(b) Gamopetalous corolla : They are of following types :

• Tubular : Five united petals form a cylindrical tubular structure, e.g., disc florets of Asteraceae.
• Infundibuliform : It is a funnel shaped corolla, e.g., Datura.
• Companulate : It is bell shaped corolla, e.g., Thevetia.

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