Biology Practical

Notes

Exercise 6

TO STUDY THE STRUCTURE AND FUNCTION OF DIFFERENT PARTS OF

FLOWERS (PETUNIA AND CHINA ROSE)

Flowering plants are classified on the basis of the structure and arrangement of floral parts
on and around the receptacle or thalamus (the swollen end part of the flower stalk) in
concentric whorls.

OBJECTIVES
After performing this exercise, you should be able to:
z identify different parts of the flower;
z recognise main features of the flowers of petunia and china rose;
z explain the structure of any type of flower.

6.1 WHAT YOU SHOULD KNOW

1. The flowering plants are classified on the basis of the structure of flowers and
arrangement of floral parts around the receptacle or thalamus.
2. This arrangement is specific for a specific family.
3. Flowers have parts such as sepals, petals, androecium, gynoecium etc.

Materials Required
(i) Flowers of china rose/hollyhock and petunia
(ii) Dissecting microscope

A. Floral Parts
Main points to be noted in these two (or in any other) flowers as follows :
(a) The size and nature of flower whether the flowers are large and showy or
inconspicuous.
(b) The origin of flower whether they are borne on the flowering twig singly/in clusters
or serially along the twig etc. (i.e. the kind of inflorescence).
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Inflorscence
(i) Main axis does not terminate in a flower-Recemose
(ii) Main axis terminates in a flower-cymose Notes

Size of the stalk whether the flowers have a long stalk (pedicellate) or they have
no stalk (sessile).

Floral parts
Each flower has to be observed starting from outermost whorl (calyx/sepals) or
epicalyx and to proceed to the inward whorls (corolla, stamens, pistils, etc.)

(a) Calyx (Sepals)

Observe and record the number of sepals, their colour and whether they are free or united.
Consult your Biology text book-1 lesson 7 and find out the function of the calyx.

(b) Corolla (Petals)

– The number of petals, their colour and shape, whether they are free or fused, their
relation with each other (overlapping, twisted, or free etc.)
– Whether the flower has both male (Androecium) and female (Gynoecium) parts
or only one of them. Thus whether the flower is bisexual or unisexual.
– Find out the function of the corolla from your text book.

(c) Androecium:
– The number of stamens, whether fused or free.
– Each stamen has an anther attached to a long filament.
– Whether the filaments are free or attached to the corolla.
– It is the male part of the flower and has pollen grains in the anther.

(d) Gynoecium (Carpels)

The gynoecium consists of carpels. One or more carpels give rise to a pistil which has
three parts-ovary, style and stigma.
– The position of the ovary on the thalamus with respect to the position of other parts—
whether above, at the same level or below i.e. inferior ovary or superior ovary.
– Number of Carpels.
– Whether the style is short or protruding out.
– The stigma, whether simple or divided into lobes or branches.
In order to find out the number of ovary chambers (locules) and the number of ovules
in each chamber, cut T.S. of ovary. In such sections you can also observe the
attachment of ovules to the ovary wall (i.e. placentation).
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Flower
Leaf
Notes

Calyx and
Epicalyx

Stigma

A Twig Style
Stigma
with Flower
Stamens and Leaves
Style A Stamen

Petal

Gynoecium
Monadelphous
Androecium

Ovary Calyx
L.S. of Flower

Fig. 6.1 Flowering twig, parts of flower of Hibiscus rosa-sinensis (China rose)

B. Symmetry
Actinomorphic
symmetrical, can be cut along more than one plane into two similar halves.
Zygomorphic
Bilaterally symmetrical can be cut into two similar halves along only one plane.
C. Aestivation
The arrangement of sepals and petals in a floral bud with respect to the members of the
same whorl.
6.2 HOW TO PROCEED
(i) Take the flower and observe the different floral parts by using hand lens/ dissecting
microscope, needles and forceps.
(ii) Note down the main features as described.
(iii) Remove the sepals one by one. Draw one of them, or the entire calyx if fused,
in your notebook.
(iv) Remove the petals. If all are similar, draw one of them otherwise each one of them
separately.
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(v) Observe the stamens and ovary. Locate their position/attachment/inter-relationship

among themselves and with other floral members.
(vi) Cut transverse sections of ovary to observe placentation and draw it in your record Notes
book.

(i) China rose

Observe the different parts of the flower carefully (Fill up observation 1)

(ii) Petunia
Observe the different parts of flower carefully (Fill up observation 2)

6.3 OBSERVATION AND DOCUMENTATION

Observation 1

(A) China-rose (Hibiscus rosasinensis)

1. Inflorescence ........................................................................................................
Draw the inflorescence
2. Pedicellate/sessile .................................................................................................
3. Sepals (Calyx)
(i) Shape ........................................................................................................
(ii) Number .....................................................................................................
(iii) Free/fused .................................................................................................
(iv) Colour .......................................................................................................
(v) Do the sepal-lobes face each other (valvate) or do they overlap (twisted)?
.................................................................................................................
(vi) Draw one sepal as you see it in your flower.
4. Petals (Corolla)
(i) Size ...........................................................................................................
(ii) Colour .......................................................................................................
(iii) Number .....................................................................................................
(iv) Free/fused .................................................................................................
(v) Do the petals face each other (valvate) or do they overlap (twisted) one above
the other by their edges?
.................................................................................................................
(vi) Draw a figure to show aestivation in corolla.

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5. Stamens (Androecium)
(i) Position (whether attached to corolla or not)
Notes
.................................................................................................................
(ii) Number .....................................................................................................
(iii) Free/Fused ................................................................................................
(iv) Are the anthers free/united ........................................................................
(v) Does the staminal tube protrude out of the flower?
.................................................................................................................
(vi) Is the anther one-lobed or four lobed?
.................................................................................................................
6. Carpels (Gynoecium)
(i) Position of ovary on the thalamus (superior/Inferior)
.................................................................................................................
(ii) Style : Is it exposed or enclosd in a tube?
.................................................................................................................
(iii) Stigma : Is it branched?
.................................................................................................................
(iv) If so, how many branches?
.................................................................................................................
(v) Take T.S. of ovary and examine and draw the diagram as you see in the
section under a dissecting microscope.
.................................................................................................................
(vi) How many chambers are there in the ovary?
.................................................................................................................
(vii) How many ovules are there inside each chamber?
.................................................................................................................

(B) Petunia
1. Draw the flower of Petunia.
2. Pedicellate/sessile
............................................................................................................................
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3. Sepal (Calyx)
(i) Number : ..................................................................................................
Notes
(ii) Free/Fused : ..............................................................................................
(iii) Colour : ....................................................................................................
(iv) Do the sepals face each other (valvate) or do they overlap (twisted)?
.................................................................................................................
(v) Draw one sepal.
4. Petals (Corolla)
(i) Number .....................................................................................................
(ii) Colour .......................................................................................................
(iii) Free/fused .................................................................................................
(iv) Valvate or twisted? ...................................................................................
(v) Draw one corolla.
5. Stamens (Androecium)
(i) Number .....................................................................................................
(ii) Position (whether attached to corolla or not) ............................................
(iii) Free/united ................................................................................................
(iv) How many lobes in each anther : .............................................................
(v) Draw a stamen indicating the filament, connective and anther lobe.
7. Carpels (Gynoecium)
(i) Position of ovary on the thalamus (Superior/inferior)
.................................................................................................................
(ii) Is the style protruding out?
.................................................................................................................
(iii) Is the style longer than the stamens?
.................................................................................................................
(iv) What is the type of placentation?
...................... (Observe T.S. of ovary under a dissection microscope)
(v) How many chambers are there in the ovary?
.................................................................................................................

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(vi) How many ovules are there in each chamber?

.................................................................................................................
Notes
(vii) Draw T.S. of ovary.

6.4 PRECAUTIONS
1. Use the needle carefully so that the floral parts are not damaged.
2. The flowers must be kept fresh by dipping the stalks in water.

6.5 FOR THE TEACHER

1. Teacher may help the students to separate out various floral parts
2. The function of flowers may be emphasised as a reproductive organ of a plant.

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