Lec8 plant flowers

Flowers
 Function
 Contain the sexual
organs for the plant.
 Produces fruit, which
protects, nourishes and
carries seeds.
 Attracts insects for
pollination.

Basic Flower Structure

stigma carpel
gynoecium
locule style Flower is perfect
pollen Flower is monoecious
ovule ovary anther

filament stamen
androecium
petal
corolla

receptacle
sepal perianth
calyx Perianth is complete
pedicel

Parts of the Flower
 Sepals
 Outer covering of the
flower bud.
 Protects the stamens
and pistils when
flower is in bud stage.
 Collectively known as
the calyx.

Parts of the Flower

 Petals
 Brightly colored
 Protects stamen &
pistils.
 Attracts pollinating
insects.
 Collectively called the
corolla.

Petal
Petals are used to attract insects into the flower, they may
have guidelines on them and be scented.
Stigma
Is covered in a sticky substance that the pollen grains will
adhere to.
Style
The style raises the stigma away from the Ovary to
decrease the likelihood of pollen contamination. It varies
in length.

Ovary
This protects the ovule and once fertilization has taken
place it will become the fruit.
Ovule
The Ovule is like the egg in animals and once
fertilization has taken place will become the seed.
Receptacle
This is the flower's attachment to the stalk and in
some cases becomes part of the fruit after fertilization
e.g. strawberry.

Flower stalk
Gives support to the flower and elevates the flower for the
insects.
Nectary
This is where a sugary solution called nectar is held to
attract insects.
Sepal
Sepals protect the flower whilst the flower is developing
from a bud.

Filament
This is the stalk of the Anther.
Anther
•The Anthers contain pollen sacs.
•The sacs release pollen on to the outside of the
anthers that brush against insects on entering the
flowers.
•Once the pollen is deposited on the insect..it is
transferred to the stigma of another flower.
•The ovule is then able to be fertilized.

Male Parts Female Parts
Stamen Pistil Ovary
Anther Stigma Ovule
Filament Style
Pollen

Parts of the Flower (Stamen)

 Male reproductive
part
 Anther
 Produces pollen

 Filament
 Supports the anther

Parts of the Flower (Pistil)
 Female reproductive
part
 Ovary
 Enlarged portion at base
of pistil
 Produces ovules which
develop into seeds
 Stigma
 Holds the pollen grains

Parts of the Flower (Pistil)
 Style
 Connects the stigma with the ovary
 Supports the stigma so that it can be pollinated

2 Types of flowers: Perfect vs. Imperfect

Imperfect- a flower that has either all male parts or all female parts

EX: cucumbers, pumpkin, and melons

Perfect- a flower that has both male and female parts in the same flower

EX: roses, lilies, and dandelions

Imperfect Flower
 Male or female
reproductive organs
not, but not both.
 Example:
 A male flower has sepals,
petals, and stamen, but
no pistils.
 A female flower has
sepals, petals, and
pistils, but no stamen.

Perfect Flowers

 Contains both male
and female
reproductive
structures.

Incomplete Flowers
 Missing one of the
four major parts of
the flower.
 Stamen
 Pistil
 Sepal
 Petal

Complete Flowers

 Contains male and
female reproductive
organs along with
petals and sepals.

Some Example Stories:
Perfect Flowers:
Pea exclusively self-pollinating
Hibiscus self-pollinating if not crossed
Cherry self-incompatible only outcrosses
Imperfect Flowers:
Begonia unisexual but monoecious
Holly unisexual and dioecious
Variable: Cucumber male, perfect, female,
parthenocarpic

Flowers
 Imperfect flowers are always incomplete but……..
 Perfect flowers are not always complete and……..
 Complete flowers are always perfect.

Importance of Flowers
 Important in florist & nursery businesses.
 Many plants are grown solely for their
flowers.
 Plants have flowers to attract insects for
pollination, but people grow them for
beauty & economic value.

Basic Flower Structure

stigma carpel
Pistil is simple
gynoecium
locule style Flower is perfect
pollen Flower is monoecious
ovule ovary
anther
superior
filament stamen
Flower is hypogynous androecium
petal
corolla
sepal perianth
receptacle
calyx Perianth is complete
pedicel

Ovary Superior
Flower Hypogynous

Ovary Half-Superior Flower Perigynous

Ovary Half-Inferior

Flower Epigynous
Ovary Inferior

NUMBER OF FLOWER PARTS

 Dicotyledonous: the flower parts are in multiples
of four or five; rarely are they in 3’s
 Monocotyledonous: the flower parts are in 3’s

NATURE OF FLOWERS
 Regular: when members of each set of organs –
the sepals, petals, stamens and pistils are of the
same size and shape
 Irregular: when some members of one or more
sets of organs are different in size or shape or both

 Irregular Flowers

 Papilionaceous: the standard petal or banner,
which is usually the largest and mostly showy of
the petals is the outermost; the wings or alae are
two lateral petals, the keels or carinae, which are
usually the two smallest petals, are innermost.
 Caesalpinaceous: the standard petal, which is
usually the smallest, is innermost; the four other
petals, which are almost of the same size and
shape, are called accessory petals.

Irregular Flowers

 Bilabiate or two-lipped: the petals are partially
united; the corolla lobes (the free ends of partially
united petals) from distinct upper and lower lips.

 Orchidaceous: the flower has three petals, one of
which is entirely different in size and shape and is
called lip or labellum.

SYMMETRY OF FLOWERS

1.Radial/actinomorphic:
one that can be divided into two equal halves
along any plane passing through the central axis.

2. Bilateral/zygomorphic:
one that can be divided only into
two equal parts by a median vertical cut.

Ovary Superior
Flower Hypogynous 1

Ovary Half-Superior
Flower Perigynous

1
Ovary Half-Inferior

Flower Epigynous
Ovary Inferior 1

TYPES OF INFLORESCENCE
Types Description

Spike Axis elongate; floret sessile,
becoming progressively younger
towards the apex
Catkin Inflorescence a spike, and partly
covered by a spathe
Raceme Axis elongate; florets pedicellate,
florets progressively becoming
younger towards the apex
Panicle A branched raceme

Cyme Axis elongate ; florets in 3s, the
central floret maturing ahead of
the other two

TYPES OF INFLORESCENCE
Types Description

Corymb Inflorescence flat-topped, the
florets growing to the same
height
Umbel Axis greatly shortened; pedicels
of the same length appearing to
radiate from a reduced axis
Head Sessile florets gathered on a flat
receptacle; some plants with
florets differentiated into the ray
and disc florets

LET US EXAMINE THE INTERNAL
STRUCTURE OF A LILY OVARY AND
ANTHER WITH POLLEN GRAINS

INTERNAL STRUCTURE

Ovary
wall

Funiculus

Locule

• Ovule-Embryonic seed consisting of
integument(s) or the protective cell layer
surrounding the ovule and nucellus or
(megasporangium) which undergoes
sporogenesis via meiosis
• Emrbyo sac-Female gametophyte
• Ovary wall- The ovary wall is the wall of the ovary
of a flower which eventually develops variously
modified in the fruit wall or pericarp
• Funiculus-Stalk by which ovule is attached to
placenta
• Locule- Ovary cavity
• Ovary-Ovule-bearing part of pistil

 plant structure that develops into a seed when
fertilized. In gymnosperms (conifers and allies) the
ovules lie uncovered on the scales of the cone.
 In angiosperms (flowering plants), one or more ovules
are enclosed by the ovary (portion of the carpel, or
female reproductive organ).
 Each ovule is attached by its base to the stalk
(funiculus) that bears it.
 A mature angiosperm ovule consists of a food tissue
covered by one or two future seed coats.

 A small opening (the micropyle) in the integuments at
the apex of the ovule permits the pollen tube to enter
and discharge its sperm nuclei into the embryo sac, a
large oval cell in which fertilization and development
occur.
 Variations in form and position of the ovule are
significant in plant classification: orthotropous ovules
stand out straight into the cavity of the ovary;
campylotropous ovules are at right angles to the
funiculus; anatropous ovules are directed back toward
the funiculus.
 Intermediate forms also occur.

• Pollen/Pollen grains- formed inside the anthers,
which are specialized parts of the stamens
• Pollen sac- Each anther lobe contains two
longitudinal pollen sacs (or locules) within
which the pollen grains are produced. A single
vascular band extends from the filament into the
center of the connective and continues into the
anther.
• Tapetum-The sporogenous tissue is delineated
from the anther wall by a single-layer of cells
designated as the tapetum. The cells of the
tapetum enlarge and develop a complex
ultrastructure, which indicates that they become
very active metabolically

• The process by which living organisms
produce their offsprings for the continuity
of the species
• One of the most important characteristic of
all living beings. It is the production of ones
own kind.
• The modes of reproduction vary according
to individual species and available
conditions.

How are new plants formed?

New plants can grow in several ways:
from seeds (sexual reproduction)- offspring is
created by fusion of haploid gametes, the egg
and sperm cells
- new individual differs genetically
From Bulbs, tubers and other vegetative parts
(asexual reproduction)- creation of new
individuals whose genes all come from one
parent without fusion of egg and sperm.
- e.g Budding, fission, sporulation and etc

Sexual reproduction
 Flowers contain a plant’s reproductive
organs. Most plants contain both male and
female parts.
 Some plants have only male sex organs while
others contain only female sex organs.
 The organs may even be separate on the
same plant (squash)

 Sexual reproduction needs special sex cells
called gametes.
 The advantage of sexual reproduction is
that it leads to genetic variation.
 If a species is varied it is more likely to be
able to adapt to any changes in its
surroundings.

In a flowering plant the flower develops on the
receptacle.
The buds of the flower are protected by sepals.
Sepals are small leaves.
 The petals of many flowers are brightly colored
which attracts insects.
These petals are often highly scented. Inside the
flower there are pin-like structures called
stamens.

 The top of the stamen produces pollen or pollen grains,
male gametophyte (microgametophyte). The club-like
structure is the stigma.
 Pollen is produced by meiosis of microspore mother
cells that are located along the inner edge of the anther
sacs (microsporangia).
 The tube cells (tube nucleus) develop to pollen tube.
 The germ cells divides by mitosis to produce two sperm
cells.
 Division of germ cell can occur before or after
pollination

 In the base of the stigma is the ovary. The ovary contains
ovules.
 Each ovule contains a female sex cell. The carpel is made up
of the stigma, style and ovary.
 When the tip of the stigma is sticky it indicates that the
carpel is ripe and ready to receive grains of pollen.
 Flowers differ in external colour, size
and shape. However they all have a
similar internal structure. Some have carpels with one
ovule, others have rows of ovules.

Cont...
 It may be simply by division of the parent cell as in
unicellular organisms, by fragmentation of the parent
body, by formation of buds and spores,or it may be
very elaborate involving development of male and
female reproductive organs (stamens and pistils).
Irrespective of the mode of reproduction, all
organisms pass on their hereditary material to their
offspring during the process of reproduction.

MODES OF REPRODUCTION
 The various modes by which plants reproduce are of
three types –

 (a) Asexual
 (b) Vegetative
 (c) Sexual

• In Asexual mode of reproduction, offspring are
reproduced from a vegetative unit-produced by a
parent without any fusion of gametes or sex cells.
– A single parent is involved
– Offsprings are genetically identical to the parent.

Asexual reproduction may be of the following types—
• Fission : As in unicellular organisms like bacteria and
yeast where the content of the parent cell divides into
2, 4 or 8 daughter cells and accordingly the fission is
known as binary or multiple fission. Each newly
formed daughter cell grows into a new organism.

 Budding : A bud like outgrowth is formed on one side
of the parent cell and soon it separates and grows into
a new individual e.g. in yeast.

 Fragmentation : In filamentous algae, an accidental
breaking of the filament into many fragments, each
fragment may give rise to a new filament of the algae
by cell division e.g. Spirogyra.

 Spore formation : In lower plants including
bryophytes and pteridophytes, special reproductive
units develop asexually on the parent body. These are
called spores. They are microscopic and covered by
protective wall. When they reach the suitable
environment they develop into a new plant body e.g. in
bread moulds, moss, fern.

 Vegetative reproduction : involves formation of
new plantlets from vegetative
-(somatic) cell, buds or organs of the plant. Here, a
vegetative part of the plant (Root, stem, leaf or bud)
gets detached from the parent body and grows into an
independent daughter plant.
-It is similar to a sexual reproduction in that it also
requires only mitotic division, no gametic fusion and
daughter plants are genetic clones of the parent plant.

• Stems, roots, leaves and even buds are variously
modified to suit this requirement. This is called
natural vegetative reproduction.
• Natural Method : In natural methods, a portion of
the plant gets detached from the body of the mother
plant and grows into an independent plant. The parts
may be stem, root, leaf or even flower.

Cont...
 The underground modification of stem, like rhizome,
(in ginger), tuber (potato), bulb (onion) and corm
(zamikand) are provided with buds which develop into
a new plant Plants with sub-aerial modification such
as Pistia (offset) and Chrysanthemum (sucker) are also
used for vegetative propagation.

-tuberous roots (Asparagus and sweet potato) can also
be used for propagation as these roots have
adventitious buds which ground into a new plant.

 leaves contribute to propagation of plants leaves of
Bryophyllum and Kalancloe have buds on the margin
and these buds grow into small plantlets. When
detached from the mother plant they grow into
independent plants.

Bryophyllum

 Agave and Oxalis multicellular bodies called bulbils
develop near the flower. These are called bulbils which
when fall on the ground grow into new plant.

Agave bulbils
Oxalis

ARTIFICIAL METHODS
 Cuttings : Many plants like rose, Bougainvillea,
Croton, Coleus, money plants, sugarcane etc. are grown
through their stem cuttings. Cuttings of these plants
can be grown even in water where they strike roots and
develop adventitious buds.

• Layering : In this method, a lower branch of a plant is
bent down and covered with moist soil leaving the
growing tip above the soil. A ring of bark is removed from
the stem before it is bent down In a few weeks time when
enough roots have developed on the underground portion
above the ringed part, it is cut off from the parent plant
and grown separately as an independent plant.
• Example: Jasmine, straw berry, grapevine, Bougainvillea
etc.

• Aerial layering or Goatee is a similar practice where
bending of branches isn’t possible because of the
height of plant or due to woody nature of stem. In this
method a ring of bark is removed from a selected
branch, and it is covered with moist moss and
enclosed in a polythene sheet when roots appear, the
stem is cut below the roots and planted to form a new
plant.

• Grafting : It is especially important for propagation of seedless
varieties of plants. It consists of inserting a small branch into a
rooted plant.
• The rooted plant taken as a stock is resistant to disease and is
physically sturdy. In this stock a branch is inserted which is known
as scion or graft. This scion or graft is the stem cutting from the
desired plant. Usually the grafted end of stock and scion fit well
with each other and are bound firmly with tape or rubber-band
until their tissues unite and vascular continuity is established.
• Grafting is mostly practised in dicot plants. Grafting has been
found extremely useful in propagating improved varieties of
various flowers and fruits like rose, Bougainvillea, Citrus, mango,
apple etc.

• MICROPROPAGATION - The technique of plant tissues
culture is utilised for propagation of plants.
-A small piece of tissue, organ or even a single cell is taken from a
plant and is transferred to a sterilized container with nutrient
medium in aseptic conditions. The tissue grows very-very fast
into an unorganised mass, called callus.
-The callus can be maintained and multiplied for an indefinite
period. When small portions of the tissue are transferred to
another specialised medium with hormones, it induces
differentiation and plantlets (little plants) are formed.
-The plantlets can be transplanted into pots and or soil by a
gradual process and are grown to mature plants.

Advantages of micropropagation
 By this method an indefinite number of identical
plants can be obtained vegetatively starting from a
small amount of parent tissue.
 In orchids, carnations, Chrysanthemum and
Asparagus, micropropagation is being successfully
tried in some parts of our country.

ADVANTAGES AND DISADVANTAGES
OF VEGETATIVE REPRODUCTION
• Advantages
-Rapid means of reproduction and spread.
- Offsprings identical to parent. The desired varieties
can thus be preserved genetically for use.
-Food storage organs allow perennation or survival in
adverse conditions.
-Improved varieties of ornamental plants and fruit trees
can be multiplied easily.
- Vegetative propagation is a quicker, easier and a less
expensive method of multiplying plants.

 Disadvantages
-Overcrowding and competition for space unless
separated artificially.
-New varieties cannot be produced by this method
except by mutation.
- Diseases typical of the species are rapidly transmitted
and can decimate a crop.

 Sexual reproduction involves fusion of male and
female reproductive cells
-(gametes) which are haploid produced by male and
female reproductive organs.
-This fusion is known as fertilization and results in
the production of a zygote (diploid). Further
development of zygote gives rise to a new
individual which is diploid.

REPRODUCTION IN ANGIOSPERMS
(FLOWERING PLANTS)

• Angiosperms reproduce both by vegetative as well as
by sexual methods. In this section we will study the
sexual reproduction in angiosperms.
• As you know sexual reproduction occurs by fusion of
male and female gametes present in the flower.
• Thus flower represents the reproductive unit of a
plant.
• Angiosperms can be classified as annuals, biennials
and perennials depending upon the time they take to
complete the life cycle and flowering.
(a) Annuals eg. pea
(b) Biennials e.g. radish
(c) Perennials e.g. mango, peepal, neem etc.
(d) Monocarpic e.g. bamboo

Factors Affecting Flowering
 Flowering in a plant is affected by temperature
(vernalisation) and light(photoperiodism).
Vernalisation : Low temperature treatment which
stimulates early flower formation is called
vernalisation.
Photoperiodism : It is the response in growth and
flowering of a plant to the duration of light and dark
period per day.
Sex in flowers : (flower, inflorescence, fruit and
families), that flowers may be bisexual (having both
stamens and carpels) or unisexual (staminate or
pistillate).

Angiosperms: Production of Male Gametophyte

Stamen = filament + anther

Meiosis inside anther
male spores

Details follow


Meiosis in lily anther 4 haploid daughter cells, also
called “pollen tetrads”

Haploi Haploi
d d

Haploi Haploi


From the point of view of the plant life cycle, anther =
male sporangium
Each of the 4 pollen tetrads = spore
Because of their small size, they are called
“microspores”.

Haploid Haploid

Pollen tetrads = microspores

Haploid Haploid


Haploi Haploi
d d
As anther matures, 4 microspores of a
tetrad separate from each other

Haploi
d

Haploid nucleus of each
Haploi microspore undergoes a single
d mitotic division
Mitosis

The 2 resulting haploid nuclei
become encased in a thick,
resistant wall, forming a pollen
grain.
Pollen Grain


Haploi Haploi
From the point of view of the
d d
angiosperm life cycle, a pollen
grain is an immature male
gametophyte, since it has been
produced by the mitotic
division of a spore.
Haploi
d

Haploi
d
Mitosis

Pollen Grain

Angiosperms: Production of Female Gametophyte

The pistil (female
reproductive portion) is
composed of the stigma,
style, and ovary.

Angiosperms: Production of Female Gametophyte

An ovary may contain a number of ovules.

Meiosis takes place inside the ovules, resulting in the production of female
spores.
Details follow

Angiosperms: Female Gametophyte

Only one of the haploid spores resulting from meiosis in the ovule
matures. It undergoes 2 rounds of mitosis to form the “embryo sac”,
which has 8 haploid nuclei.

Embryo sac = female gametophyte

Alternation of Generations: Angiosperms

To complete the life cycle,
the gametes produced by
the male and female
gametophyte must unite,
restoring the diploid
sporophyte.

Female gametophyte = embryo sac

Immature male gametophyte = pollen grain

 Pollination : Transfer of pollen grains from the
anther to the stigma of flower.

1. Pollination by wind (Anemophily) : (Anemos :
wind, Phile: to love)
-example, grasses and some cacti.
2. Pollination by insects (Entomophily) : (entomo :
insect, phile : to love)
-Salvia flowers show special adaptations for pollination
by bees.
3. Pollination by Water (Hydrophily) (Hydros :
water)
-e.g. Hydrilla, Vallisneria.
4. Pollination by Animals (Zoophily) (Zoon :
animal)
-example sun bird, pollinates flowers of Canna, gladioli
etc., Squirrels pollinate flowers of silk cotton tree.

Fertilization and Embryo Formation

Pollen grain
landing on
stigma of ovary
pollen tube
growth


2 haploid cells of pollen
grain are called the
“generative cell” and the
“tube cell”

Pollen tube growing from a
pollen grain


As pollen tube grows
towards ovule,
nucleus of
“generative cell”
divides by mitosis,
producing 2 haploid
sperm


The pollen grain,
along with the
pollen tube
containing 2
sperm, is the
mature male
gametophyte.


Pollen tube continues to grow,
entering ovule through opening
called the “micropyle”


One of the sperm fertilizes the egg, producing a
diploid zygote. This zygote will divide and
differentiate, forming the sporophyte plant.
The angiosperm life cycle has been completed.

The other sperm will fuse with
the 2 central haploid nuclei in the
embryo sac, producing a triploid
nucleus.

These events are called “double
fertilization”.


Tissue that develops from the triploid nucleus =
“endosperm”. Energy stored in this tissue nourishes the
developing embryo.

“Don’t make me read, make me understand “

THANK YOU!!!

Flower Structure - review Ranunculus acris - buttercup

Flower Formula: Symbol Sequence to Diagram Flower
Symmetry: *=radial †=bilateral
* 5, 5, , 5
Number of Parts per Whorl:
• sepals in calyx
• petals in corolla
• stamens in androecium
• carpels in gynoecium

Fusion within whorl:
curved line over number

Fusion between whorls:
square bracket below numbers

Attachment of flower parts relative to ovary:
horizontal line

Lec8 plant flowers

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