THE SEED
Seed is a ripened ovule which contains an embryo or tiny
plant with sufficient reserve food for the development Of
embryo.
The ovules after fertilisation develop into seeds. A seed is
made up of seed coats and an embryo. The embryo is made
up of a radicle, an embryonal axis and one (wheat an
maize) or two cotyledons (gram and pea).
Types of Seeds
Seeds can be classified into two different types based on the
number of cotyledons and presence or absence of endosperms,
i.e., dicotyledonous and monocotyledonous seed.
i. Dicotyledonous Seed
Gram seed is a dicot seed formed in a small pod or legume. The
outermost covering is the seed coat. An endosperm is absent.
Structure of Dicotyledonous Seed
Seed can be studied under two heads, i.e., external structure
and internal structure.
It is light or dark brown in colour. Its surface may be smooth
or wrinkled. A small oval scar present at the side called hilum.
It is the point where the stalk or funicle of the seed is attached
to it. A narrow ridge called raphae runs from hilum to chalaza
inside the furrow. A small pore called micropyle present
between the hilum and pointed end.
The outermost covering of the seed is seed coat. The outer hard
and leathery layer of the coat is called testa and the inner thin
and membranous layer is the tegmen. In some s
tegmen and testa are fused.
The seed coat encloses the embryo, which is differentiated into
a radicle, a plumule and cotyledons. The radicle develops into
root and plumule into shoot. Cotyledons may be one or two to
serve as reserve food.
Hypocotyl is a part present between the point of attachment of
cotyledon and radicle. Epicotyle is present between point of
attachment of cotyledons and plumule.
In some seeds, such as castor seeds, the endosperm is formed as a
result of double fertilisation, which is a storing tissue. In
plants like bean, gram and pea, the endosperm is not present in
mature seeds (i.e., non-endospermous seeds).
ii. Monocotyledonous Seed
The monocotyledonous seeds are endospermic, but some as in
orchids are non-endospermic. In the cereals, such as maize, the
seed coat is membranous and generally fused with the fruit
wall.
Structure of Monocotyledonous Seed
The endosperm is bulky and stores food. The outer
covering of endosperm separates the embryo by a
proteinous layer called aleurone layer. The embryo is
small and situated in a groove at one end of the
endosperm. It consists of one large shield-shaped
cotyledon known as scutellum and a short axis with a
plumule and a radicle. The plumule and radicle are
enclosed in sheaths which are called coleoptile and
coleorhiza, respectively.
Coleoptile has a terminal pore for the emergence of first
leaf is capable of
growth. It helps the future shoot in passing through the soil
during germination, e.g., maize grain is whitish, yellow,
violet or red in colour. It has smooth or shiny surface.
Its grain is covered with a single, thin hard covering. It
is formed by the fusion of seed coat or testa and the
fruit wall or pericarp.

THE FLOWER
A flower is the reproductive unit in the angiosperms.
It is meant for sexual reproduction.
Morphologically, it is considered as a shoot bearing
nodes and modified floral leaves. Flower is
modified shoot because the position of the buds in
both flower and shoot is same and can be in terminal
or axillary in position.
Structure of Flower
A flower arises at the axil of a leaf-like structure called bract.
Flowers with bracts are called bracteate and those without bracts
are called ebracteate.
The terminal and swollen part of the axis of the flower is the
receptacle or thalamus. The receptacle contains four different
types of whorls arranged in successive mode sepals, petals, stamens
and carpels. If the leaves are present on the pedical, they are called
bracteoles.
Parts of a Flower
A typical flower consists of four distinct parts the calyx, the corolla,
the androecium and the gynoecium. The calyx and corolla are
accessory parts and the androecium and gynoecium are essential
parts.
These essential parts consist of two kinds of sporophylls, the
microsporophyll (male) and the megasporophyll (female).
A flower can be unisexual or bisexual. It is borne on short or long
axis. The axis contains two regions the pedicel and the thalamus or
receptacle. The pedicel may be short, long or even absent. The
thalamus is the swollen end of the axis on which the floral whorls
are arranged.
Different whorls present on flower are given below
i. Calyx
It is the outermost whorl of a flower. It is made up of units like
sepals. The sepals are generally green, leaf-like and protect the
flower in the bud stage. They have veins and stomata like ordinary
leaves, but are thicker in nature. The sepals may be gamosepalous
(sepals united), e.g., Caesalpinia or polysepalous (sepals free), e.g.,
Crotalaria.
The sepals also prevent transpiration from inner parts of the
flower. Coloured sepals attract insects for pollination.
ii. Corolla
It is composed of petals. Petals are usually brightly coloured to
attract insects for pollination. Like calyx, corolla may also be
gamopetalous (petals united) or polypetalous (petals free). The
shape and colour of corolla may vary greatly in shape. Corolla may
be tubular, bell-shaped, funnel-shaped.
iii. Androecium
It is the third whorl of flower composed of stamens or
microsporangium. Each stamen, which represents the male
reproductive organ consists of a stalk or a filament and an
anther. Each anther is usually bilobed which are attached at
the back by a sterile band called connective and each lobe
has two chambers, the pollen sacs. The pollen grains are
produced in pollen sacs. A sterile stamen is called staminode
(without anther). Stamens can be of different types
depending on their union with other members such as petals
or among themselves.
(a) When stamens are attached to the petals, they are
epipetalous, e.g., brinjal.
(b) When stamens are attached to the perianth, the
condition is called epiphyllous, e.g., lily.
(c) The stamens in a flower may either remain free, i.e.,
polyandrous or may be united in varying degrees.
(d) The stamens may be united into one bunch or one
bundle, i.e., monoadelphous as in China rose. It
may be two bundles, i.e., diadelphous as in pea or
into more than two bundles, i.e., polyadelphous as in
citrus.
(e) There may be a variation in the length of filament.
in Salvia and mustard.
iv. Gynoecium
Gynoecium is the female reproductive part of the flower. It
is made up of one or more carpels or megasporangium
Megaspores are produced within the megasporangium. A
carpel consists of three parts, i.e., stigma, style and ovary.
The stigma is usually at the tip of style and is the receptive
surface for pollen grains.
Ovary is the enlarged basal part on which lies the elongated
tube, the style.
The style connects the ovary to the stigma. Each ovary bean
one or more ovules attached to a flattened, cushion-like
placenta
Depending on the number of carpel present, may be freed
united, gynoecium can be of following types
(a) Apocarpous When more than one carpel is present
they may be free are called apocarpous, e.g.,
low:
and rose.
(b) Syncarpous When carpels are fused together,
gynoecium is called syncarpous, e.g., brinjal at’
Hibiscus.
Locules in the Ovary
The cavity enclosed by the ovary wall is called locule.
number of locules in the ovary correspond to the number
carpels in the gvnoecium, i.e., unilocular (only one
e.g., pea), bilocular (two locules, e.g., tomato),
trilocular (three locules, e.g., Ricinus), multilocular (mam
locules. e.g., orange and lemon).
Placentation
The arrangement of ovules within the ovary is known
placentation. The placenta is a tissue, which develops along
the inner wall of the ovary. The ovule or ovules remain
attached to the placenta.
The placentation can be of different
(a) Marginal The placenta forms a ridge along the
ventral suture of the ovary and the ovules are
on this ridge forming two rows is called marginal
placentation, e.g., pea.
(b) Axile When the placenta is axial and the ovule
attached to it in a ovary, the placentation
is called axile, e.g., China rose, tomato and lemon
(c) Parietal When the ovules develop on the inner wall
of the ovary or on peripheral part, it is called parietal
placentation. Ovary is one-chambered. but
becomes two-chambered due to the formation
false septum, e.g., mustard and Argemone.
(d) Free central When the ovules are borne on central
axis and septa are absent, the placentation is called
free central, e.g., Dianthus and primrose.
(e) Basal In this type, the placenta develops at the base
of ovary and a single ovule is attached to it as in
sunflower, marigold. The placenta develops directly
on the thalamus.
Insertion of Floral Parts
(Forms of Thalams)
The positions of different whorls of flowers are different.
This is due to the position of ovary.
Thoe positions may be of three types
i. Hypogynous Flower
The thalamus is conical, dome-shaped or flat. The ovary is
present at the top of thalamus. The stamem, petals and
sepals are separate and successively inserted below the ovary.
Ovary is superior, whereas rest of the structures are inferior.
e.g., Brassica, Hibiscus, Petunia.
ii. Perigynous Flower
The margin of thalamus grows upwards forming a cup-like
structure called calyx tube. The calyx tube encloses ovary,
but remains free from it and the sepals, petals and stamens
are present in it. The ovary is half inferior, e.g., rose, plum,
peach, etc.
iii. Epigynous Flower •
The thalamus grows upwards to completely cover the ovary
and also fused inseparably with the latter. The other floral
parts are borne at the top of the fused thalamus and ovary.
The ovary is called inferior, e.g., Helianthto (sunflower),
Cucurbita (pumpkin), Pynus (apple).
ymmetry of A Flower
e symmetry of a flower depends upon the shape, size and
rangement of floral parts, e.g., calyx, corolla, androecium
d gynoecium. Flowers can be actinomorphic and
gomorphic on the basis of symmetry.
Actinomorphic
n this type, a flower can be divided into exactly equal
halves by any vertical section passing through the centre of a
flower, e.g., mustard, Datura.
ii. Zygomorphic
In this type, flower can be divided into two identical halves
through only one particular vertical plane, e.g., Ocimum,
Cassia.