The flower is defined as a modified shoot meant for sexual reproduction.

1. Flower
Department Of Botany
Prepared by
Dr. P. B. Cholke
(Assistant Professor in Botany)
Pune District Education Association’s
Anantrao Pawar College ,Pirangut,
Tal-Mulshi, Dist-Pune- 412115

2. • Flower is defined as modified shoot meant
for sexual reproduction.
• Flower has thalamus – the floral axis which is
a shortened stem bearing four nodes and
three internodes.
• The four nodes bears four whorls in the order
from base as –a) Accessory whorls=
• calyx( Sepals), corolla(petals),
• b) Essential whorls= androecium( Stamens)
and gynoecium (Carpels)

3. The Parts of a Flower
• Most flowers have
four parts:
• sepals,
• petals,
• stamens,
• carpels.
• Their site of
attachment to the
stem is the receptacle
Pedicel – connection
between flower and
stem

4. • Sepals and petals are non reproductive
organs.
1. Calyx (Sepals) :
– It is outermost first whorl of flower.
– Sepals are usually green and more leaf like in
appearance.
– Sepals protect the inner whorl of the flower
2. Corolla ( Petals):
– It is second whorl of flower.
– In many angiosperms, the petals are brightly
colored and help to attract the insects and other
pollinators for pollination.

5. • Stamens (male) and carpels (female) are reproductive
organs.
3. Androecium:
 It is the third whorl of flower and consist of cylindrical
structures called stamens which are male reproductive organs.
 A stamen consists of a stalk (the filament) and a terminal anther
within which are pollen sacs.
 The pollen sacs produce pollen.

7. 4. Gynoecium:
– It is the innermost ( fourth)whorl of flower. Which has Carpels.
They are the female reproductive organs of flowers.
– A carpel has an ovary at the base and a slender neck, the style.
• At the top of the style is a sticky structure called the
stigma that serves as a landing platform for pollen.
• Within the ovary are one or more ovules.
• Some flowers have a single carpel, in others, several
carpals are fused into a single structure, producing an
ovary with two or more chambers.

8. • Structure of anther
• * Anther is the part of the stamen. Anther in
angiosperm is usually dithecous (two lobed).
• * Dithecous anther is tetrasporangiate i.e. it consist
of four microsporangia.
• * Two anther lobes are connected by sterile tissue
called connective.
• * The process of formation of microspores is called
microsporogenesis.
• * Microsporogenesis occurs in microsporangium.

10. T.S. of anther

11. • Anther lobe
enlarged

12. • T. S. of anther show presence of anther wall,
epidermis, endothecium, middle layers, tapetum,
micosporangium and pollen grains.
• 1 Epidermis :
 It is outermost layer of anther wall.
 It consist of flattened, compactly arranged cells.
 Function: It is protective layer.
• 2 Endothecium :
 It is single layer present below the epidermis.
 The cells of endothecium develop fibrous thickening of
callose on their walls.
 Cells of endothecium are hygroscopic in nature .
Function: help in dehiscence of anther.

13. • 3 Middle layers :
 It is present Below the endothecium
 It is 1-3 layered and made up of parenchyma cells.
 Function: cells of these layers degenerates at maturity.
• 4 Tapetum :
 It is the innermost layer of anther wall.
 It consist of radially elongated, multinucleated
(polyploid nucleus) cells .
Functions:
1. Cells of tapetum provides nourishment to the
developing microspores( Pollen grains).
2. It involved in the formation of sporopollenin.
3. Ubisch bodies of tapetum forms pollenkit in
entomophilous flowers.

14. • 5 Microsporangium or Pollen sac :
i. An anther consist of two anther lobes
ii. Each anther lobeis with two pollen sacs.
iii. The pollen sac encloses primary sporogenous
tissue ( 2n)which divides mitotically to from
diploid pollen mother cells.( PMC)
iv. The process of formation of haploid spores
from the PMC by meiotic division is called
Microsporogenesis. It occurs inside the pollen
sac ( Microsporangium).
v. Initially all the microspores remains in groups
of four called tetrads. It is mostly tetra hedral
tetrad.

15. • Structure of pollen grain :
– Pollen grain is unicellular, uninucleate haploid in structure.
– It is the first cell of male gametophyte.
– The wall of pollen grain has two layers called sporoderm.
A) Exine:
The outer wall of pollen grain is called exine.
i. It is thick and hard wall .
ii. It is made up of sporopollenin which is resistant to chemical and
biological degradation.
iii. Exine is covered by yellowish, viscous sticky substance called pollen kit.
iv. The exine shows one or more depressed regions called germpores
through which pollen tube germinates.
– In monocots pollen grain is uniporate and
– in dicots pollen grain is mostly triporate.
– Function of Exine: Protection of pollens.
B) Intine:
Inner wall of pollen grain is called intine.
i. It is thin , smooth and elastic wall.
ii. It is made up of pectin and cellulose.
Function of intine: it covers the germinating pollen tube.
– The branch of botany which deals with the study of pollen grains is called
palynology

16. • Development of male gametophyte :
• * It also called microgametophyte It is highly
reduced (only three celled).
• * Development of male gametophyte starts in
pollen grain therefore called endosporic.
• Pollen grain divides mitotically to from a two
celled male gametophyte.
• The smaller cell is called generative cell
• while larger cell is called vegetative cell or tube
cell.

17. • Pollen grain is deposited on stigma at two celled stage (in 60%
angiosperms).
• In some angiosperms (about 40%), the pollen grains are
released at 3-celled stage i.e. with a tube cell and two male
gametes.
• * Generative cell may be elliptical or spindle shaped.
Nucleus is large and cell do not possess vacuoles and much of
stored food material.
• * Due to the absence of definite cell wall generative cell is
suspended freely in cytoplasm of vegetative cell.
• * Two celled pollen grain absorb water and nutrients from
the stigmatic secretion (Sugary substances and Boron)
through its germ pore and swells.
• * The exine ruptures and tube cell projects out through one
of the germ pore in the from of germ tube or pollen tube.
• * The generative cell divides mitotically to form two non
motile male gametes (microgametogenesis).
• * Pollen tube carries two male gametes the process is called
siphonogamy.

19. TYPES OF OVULES

25. • Structure of anatroprus ovule : -
• Ovule is called fore runner of the seed. Ovules are
enclosed within the ovary.
• Ovule is integumented megasporangium.
• In most (about 82%) of the angiosperms the ovule
is anatropous i.e. inverted.
• The ovule in which micropyle is directed towards
the funicle is called anatropous ovule.
• The development of female gametophyte occurs
inside the ovule.
• In anatropous ovule, a longitudinal ridge is present
on one side of ovule called raphe.

26. • I. Funicle :
• Stalk of ovule is called funicle or funiculus. Each ovule is
attached to the placenta by means of funicle. Placenta is
a fertile tissue in the ovary to which ovules are attached.
• II. Hilum :
• The point of attachment of funicle to the body of ovule is
called hilum.
• III. Nucellus :
• It is central major part of the ovule made up of thin
walled, diploid, parenchymatous nutritive tissue. It is
also called megasporangium proper.
• Megasporogenesis and development of female
gametophyte takes place in megasporangium.
• Function: Nucellus provides nourishment to the
developing embryo sac.

27. • IV. Chalaza :
• A basal swollen part of the nucellus from which
integuments arises is called Chalaza.
• V. Integuments :
• The nucellus is protected by two multicellular coverings
called integuments.
• Angiospermic ovule is mostly bitegmic.
• Function: Integuments form seed coat after the
fertilization.
• VI Micropyle :
• A small opening in the integuments at the apex of ovule is
called Micropyle.
• Function: It gives entry to the pollen tube of male
gametophyte.
• It allows the entry of water during the seed germination.

28. • VII Female gametophyte/Embryo sac:
• Nucellus of matured ovule shows the presence of oval shaped haploid
structure at micropylar end called embryo sac.
• It is 7 celled and 8 nucleated.
• It consist of .
• a) An Egg Apparatus:
• A group of three haploid cells towards the micropylar end from the egg
apparatus.
• Which consist of an egg cell and two synergids or help cells.
• After fertilization egg cell gives rise to diploid zygote .
• The filiform apparatus of synergids attracts pollen tube during fertilization
• b) Antipodal cells:
• A group of three haploid cells towards the chalazal end called antipodals.
• Antipodal cells degenerates after fertilization.
• c) Secondary Nucleus:
• A single, large central cell contains two haploid polar nuclei at the centre
called secondary nucleus.
• One male gamete fuses with diploid secondary nucleus to from TPEN.(
Triploid Primary Endosperm Nucleus)
• TPEN undergoes mitotic division to from endosperm.

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