- Flower: It is a modified shoot, highly specialised for sexual
- Thalamus: It is the basal portion of a flower from where
the floral whorls arise.
- Pedicel: Stalk of the flower.
- Floral Whorls: Floral members are arranged on the thalamus in
a cyclic manner one inside the other, thus called whorls.
are four whorls namely calyx, corolla, androecium and gynoecium.
of these, calyx and corolla are accessory whorls while
androecium and gynoecium are called essential whorls.
of calyx are sepals, corolla are petals,
androecium are stamens and gynoecium are carpels.
calyx and corolla are not differentiated. Such undifferentiated whorl
is called 'perianth'. The members of perianth are tepals.
- Complete Flower: When a flower contains all the four floral
whorls, it is called a complete flower.
- Incomplete Flower: When one of the floral whorls is missing, the
flower is called incomplete flower.
- Bisexual and unisexual flower: When a flower
contains, both the essential whorls, i.e., stamen as well as carpel,
then the flower is bisexual. But if
only one essential whorl is present i.e., either
stamen or carpel then it is called unisexual flower.
flower is called 'staminate' flower while female flower is
called 'pistillate' flower.
upon the arrangement of floral whorls on the thalamus, with respect
to position of ovary, there are three types.
- Hypogynous Flower: Here thalamus is elongated and ovary is superior
in position. Stamen, petals and sepals are situated below ovary.
Example: Hibiscus flower.
- Epigynous Flower: Here thalamus is cup-shaped and ovary is
present in this cup-like thalamus. Thus it is inferior and
other whorls arise from the top of ovary. Example: Guava flower.
- Perigynous Flower: Here, the thalamus is cup-shaped. Stamens,
petals and sepals arise from the cup-shaped thalamus. They encircle
the ovary. Example: Rose.
- Inflorescence: It is a branch system which bears flowers. The
stalk of inflorescence is called 'peduncle'.
main types of inflorescence are 'cymose' and 'racemose'.
- Racemose: Here, the growth of peduncle is indefinite.
The flowers arranged are in 'acropetal' succession, i.e., older
flowers at the base and younger towards apex.
- Cymose: Here, the growth of peduncle is limited because peduncle
ends in a flower. The flowers are arranged in 'basipetal'
succession, i.e., younger flowers at the base and older flowers at
- Pollination: Transfer of pollen grains from anthers to the
stigma is called pollination.
- Types of Pollination: Two main types of pollination are 'self
pollination' and 'cross pollination'.
- Self Pollination: Also called 'autogamy'. Here, pollen
grains are transferred from anthers to the stigma of same flower.
- Cross Pollination: Also called 'allogamy'. Here, pollen
grains are transferred from anthers to the stigma of other flower.
For this transfer of anthers, some pollinating agents are required.
pollinating agent is wind, it is called 'anemophily'.
Pollination by water is called 'hydrophily' while pollination
by animals is called 'zoophily'.
self pollination to take place, the flowers should be 'bisexual',
i.e., stamens and carpels both should be present and they should
mature at one time, i.e., 'Homogamy'.
some plants, the flowers do not open at all. In such closed flowers,
self pollination becomes a rule. This is 'cleistogamy'.
cross pollination to take place, the flowers should have attractive
colours, sufficient large size, presence of spiny, sticky pollen
grains and nectarines to produce sugary solution.
flowers should be 'unisexual', i.e., either stamen or carpel
should be present and their maturity time should be different. If
anthers mature first, it is 'protandry' and if gynoecium
matures first, it is 'protogyny'.
seen in the flower to carry out a specific type of pollination is
called 'contrivances'. For cross pollination, if the lengths
of styles is different i.e., 'Heterostyly', then only cross
pollination takes place. If pollens of the same flowers do not
germinate on its stigma, then cross pollination takes place. This is
plant is diploid and produces two types of haploid spores called microspores
typical anther is made up of two anther lobes. Each anther lobe
contains microspore (pollen) mother cells. These microspore mother
cells undergo meiosis and produce haploid microspores.
pollen or microspore is with two coverings, namely, outer 'exine'
and inner 'intine'. Exine shows 'germ pores'.
unicellular pollen divides unequally to give tube cell and generative
cell. This bicelled structure is 'male gametophyte'. Tube
cell helps in the formation of pollen tube and generative cell forms
two male gametes.
the ovary ovules are present which are arranged on a special tissue
ovule consists of a central mass of tissue called 'nucellus'.
The nucellus is covered over by two protective layers called 'outer
and inner integuments'.
integuments leave an aperture at one end. It is called 'micropyle'
through which pollen tube enters during fertilisation. This end of
ovule is called 'micropylar end' while opposite end is called
stalk of ovule is called 'funicle'.
of the cells of nucellus becomes large to form 'megaspore mother
cell', which undergoes meiosis to produce 'four megaspores'.
of four, three degenerate and one megaspore remains functional which gives rise to 'female gametophyte', i.e., embryo
development, nucleus of functional megaspore undergoes successive
divisions, to form eight nuclei. Out of these eight nuclei, three
are at one end, three at the opposite end and two in the middle
group of three nuclei at chalazal end is called 'antipodal cells'.
The nuclei in the centre are called 'secondary nucleus'. Out
of the three nuclei at micropylar end, the central large cell is 'egg'
cell and the other two are called 'synergids'. The egg with
two synergids is called 'egg apparatus'.
- Fertilisation: Fusion of male and female gametes is called
grains on the stigma absorb moisture and produce pollen tube which
passes through the style and reaches the ovule.
tube carries two male gametes. It enters the ovule through micropyle
and reaches the embryo sac.
tip of the pollen tube ruptures and two male gametes are released in
the embryo sac.
of two male gametes, one fuses with the egg cell to form zygote
while the other fuses with the secondary nucleus to form primary
act where both the male gametes participate in the fertilisation is
called 'double fertilisation'.
significance of double fertilisation is formation of a triploid
tissue which is nutritive in function, and nourishes the developing
fertilisation, the ovary forms fruits, ovules form seeds and the two
integuments form seed coats called testa and tegmen.
fusion product of male and female gametes results into 'zygote'
which after a short resting period divides by mitosis to give rise
the zygote divides to form a two-celled stage called 'proembryo'.
These two cells are 'basal cell' and 'terminal cell'.
cell forms 'suspensor' and terminal cell forms 'embryo
cell divides to give rise to eight-celled structure called 'octant'.
terminal cells from octant forms cotyledons
and plumule. Four basal cells form radicle and hypocotyl.
some seeds, during the development, the endosperm is completely used
by the developing embryo. Thus, the seeds are without endosperm and
are called 'non-endospermic' or 'ex-albuminous' seeds.
Example: Pea, bean.
seeds which contain endosperm at maturity are called 'endospermic'
or 'albuminous' seeds. Example: Maize, castor.
is the fertilised ovary. It has a covering called 'pericarp'
which may be 'dry' or 'fleshy'. The pericarp consists of outer
'epicarp', middle 'mesocarp' and inner 'endocarp'.
In most of the fleshy fruits, the mesocarp is thick, fleshy and
edible but in coconut it is fibrous.
a fruit develops from the ovary, it is called a true fruit.
Sometimes the fruit may develop from parts other than ovary such as
thalamus. Such fruit is called a false fruit or pseudo
fruit. For example, in cashew, peduncle forms a fruit while in
apple it is thalamus.
fruit is either simple or aggregate or composite.
fruit is formed from a single ovary. Simple fruits are of two types,
namely, dry and fleshy. Some simple, dry fruits do not split or
dehisce. They are called indehiscent fruits. Example: Achene,
caryopsis, cypsela, nut, etc. Some simple dry fruits spilt or
dehisce along one or more margins. They are called dehiscent
fruits. Example: Legume, follicle, capsule, siliqua.
aggregate fruit, a combined fruit is formed from different free
carpels of the same flower. Example: Strawberry, custard apple, etc.
composite fruit, an inflorescence gives rise to a single fruit.
Example: Fig, jackfruit, etc.
the ovary develops into a fruit without fertilisation. This is
called parthenocarpy. Parthenocarpic fruits are seedless.
Example: Banana, pineapple, etc.