Tuesday, November 27, 2012

Morphology of flowering plants

Morphology of flowering  Plants

Morphology : The study of various external features of the organism is known
as morphology.

Adaptation : Any alteration in the structure or function of an organism or any of
its part that results from natural selection and by which the organism becomes
better fitted to survive and multiply in its environment.

The Root : The root is underground part of the plant and develops from elongation
of radicle of the embryo.

Various types of root:

Tap root ,Fibrous root ,Adventitious root and they
Originates from radicle. Originates from base of the stem. Originates from parts of the plant
other than radical respectively.

Root Cap : The root is covered at the apex by the thumble-like structure which
protects the tender apical part.

Regions of the root :
1. Region of meristematic activity : Cells of this region have the capability
to divide.
2. Region of elongation : Cells of this region are elongated and enlarged.
3. Region of Maturation : This region has differentiated and matured cells.
Some of the epidermal cells of this region form thread-like root hairs.

Modifications of Root :
Roots are modified for support, storage of food, respiration.

• For support : Prop roots in banyan tree, stilt roots in maize and
sugarcane.
• For respiration : pneumatophores in Rhizophora (Mangrove).
• For storage of food : Fusiform (radish), Napiform (turnip), Conical
(carrot).

The Stem : Stem is the aerial part of the plant and develops from plumule of the
embryo. It bears nodes and internodes.

Modifications of Stem :
In some plants the stems are modified to perform the function of storage of
food, support, protection and vegetative propagation.

Food Storage: Stems are modified to perform different functions. Underground
stems of potato, ginger, turmeric, zaminkand, Colocasia are modified to store food in
them. They also act as organs of perenation to tide over conditions unfavourable for
growth.

Tendrils: Stem tendrils which develop from axillary buds, are slender and spirally
coiled and help plants to climb such as in gourds (cucumber, pumpkins, watermelon)
and grapevines.

Thorns: Axillary buds of stems may also get modified into woody, straight and
pointed thorns. Thorns are found in many plants such as Citrus, Bougainvillea. They
protect plants from browsing animals.

Vegetative Reproduction: Underground stems of some plants such as grass and
strawberry, etc., spread to new niches and when older parts die new plants are
formed. In plants like mint and jasmine a slender lateral branch arises from the base
of the main axis and after growing aerially for some time arch downwards to touch
the ground. A lateral branch with short internodes and each node bearing a rosette
of leaves and a tuft of roots is found in aquatic plants like Pistia and Eichhornia. In
banana, pineapple and Chrysanthemum, the lateral branches originate from the
basal and underground portion of the main stem, grow horizontally beneath the soil
and then come out obliquely upward giving rise to leafy shoots.

 For assimilation of food : Flattened stem of opuntia contains chlorophyll
and performs photosynthesis.

The Leaf : Developes from shoot apical meristem, flattened, green structure,
manufacture the food by photosynthesis. It has bud in axil. A typical leaf has leaf
base, petiole and lamina
.
Types of Leaf
Simple 
(Single leaf blade) (Leaf has number of leaflets)
e.g., mango, peepal
 Compound: Pinnately, Palmately types are 
(Neem, rose) (Silk cotton) respectively.

Venation : The arrangement of veins and veinlets in the lamina of leaf.
Types of Venation :
1. Reticulate : Veinlets form a network as in leaves of dicotyledonous plants
(China rose, peepal).
2. Parallel : Veins are parallel to each other as in leaves of monocotyledonous
plants (grass, maize, sugarcane).
Phyllotaxy : The pattern of arrangement of leaves on the stem or branch.

Types of phyllotaxy:
Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. This is
usually of three types – alternate, opposite and whorled.
Alternate Arrangement of Leaves: In alternate type of phyllotaxy, a single leaf
arises at each node in alternate manner, as in china rose, mustard and sun flower
plants.
Opposite Arrangement of Leaves: In opposite type, a pair of leaves arise at each
node and lie opposite to each other as in Calotropis and guava plants.
Whorled Arrangement of Leaves: If more than two leaves arise at a node and
form a whorl, it is called whorled, as in Alstonia.


Modifications of Leaves :
• Tendrils : (Climbing) − Sweet wild pea
• Spines : (Protection) − Aloe, Opuntia, Argemone
• Piture : (Nutrition) − Nepenthes
• Hook : (Support) − Cat’s nail

Inflorescence : The arrangement of flowers on the floral axis.
Main types of Inflorescence :
1. Racemose : Radish, Mustard, Amaranthus.
2. Cymose : Cotton, Jasmine, Calotropis.
3. Special type : Ficus, Salvia, Euphorbia.

The Flower : A flower is modified shoot. It is a reproductive unit in angiosperms.
Flowers may be unisexual or bisexual, bracteate or ebractiate.

Parts of flower :
The flower is the reproductive unit in the angiosperms. It is meant for sexual
reproduction. A typical flower has four different kinds of whorls arranged
successively on the swollen end of the stalk or pedicel, called thalamus or
receptacle. These are calyx, corolla, androecium and gynoecium. Calyx and corolla
are accessory organs, while androecium and gynoecium are reproductive organs. In
some flowers like lily, the calyx and corolla are not distinct and are termed as
perianth.
Parts of a Flower:-



Each flower normally has four floral whorls, viz., calyx, corolla, androecium and
gynoecium.

Calyx: The calyx is the outermost whorl of the flower and the members are called
sepals. Generally, sepals are green, leaf like and protect the flower in the bud stage.
The calyx may be gamosepalous (sepals united) or polysepalous (sepals free).
Corolla: Corolla is composed of petals. Petals are usually brightly coloured to
attract insects for pollination. Like calyx, corolla may be also free (gamopetalous)
or united (polypetalous). The shape and colour of corolla vary greatly in plants.
Corolla may be tubular, bell-shaped, funnel-shaped or wheel-shaped.
Androecium
Androecium is composed of stamens. Each stamen which represents the male
reproductive organ consists of a stalk or a filament and an anther. Each anther is
usually bilobed and each lobe has two chambers, the pollen-sacs. The pollen grains
are produced in pollen-sacs. A sterile stamen is called staminode. Stamens of
flower may be united with other members such as petals or among themselves.
When stamens are attached to the petals, they are epipetalous as in brinjal, or
epiphyllous when attached to the perianth as in the flowers of lily. The stamens in a
flower may either remain free (polyandrous) or may be united in varying degrees.
The stamens may be united into one bunch or one bundle (monoadelphous) as in
china rose, or two bundles (diadelphous) as in pea, or into more than two bundles
(polyadelphous) as in citrus. There may be a variation in the length of filaments
within a flower, as in Salvia and mustard.
Gynoecium
Gynoecium is the female reproductive part of the flower and is made up of one or
more carpels. A carpel consists of three parts namely stigma, style and ovary. Ovary
is the enlarged basal part, on which lies the elongated tube, the style. The style
connects the ovary to the stigma. The stigma is usually at the tip of the style and is
the receptive surface for pollen grains. Each ovary bears one or more ovules
attached to a flattened, cushion-like placenta. When more than one carpel is
present, they may be free (as in lotus and rose) and are called apocarpous. They
are termed syncarpous when carpels are fused, as in mustard and tomato. After
fertilisation, the ovules develop into seeds and the ovary matures into a fruit.
Gamosepalous − (Sepals united)
Polyseptalous − (Sepals free)
Gamopetalous − (Petals united)
Polypetalous − (Petals free)

Perianth : If calyx and corolla are not distinguishable, they are called perianth.

Aestivation : The mode of arrangement of sepals or petals in floral bud.

Types of aestivation :
1. Valvate : Sepals or petals do not overlap the sepal or petal at margins.
2. Twisted : Sepals or petals overlap the next sepal or petal.
3. Imbricate : The margins of sepals or petals overlap one another but not
in any definite direction.
4. Vexillary : The largest petal overlaps the two lateral petals which in turn
overlap two smallest anterior petals.


Placentation: The arrangement of ovules within the ovary is known as
placentation. The placentation are of different types namely, marginal, axile,
parietal, basal, central and free central.
1.Marginal: In marginal placentation the placenta forms a ridge along the ventral
suture of the ovary and the ovules are borne on this ridge forming two rows, as in
pea.
2.Axile: When the placenta is axial and the ovules are attached to it in a multilocular
ovary, the placentaion is said to be axile, as in china rose, tomato and lemon.
3.Parietal: In parietal placentation, the ovules develop on the inner wall of the ovary
or on peripheral part. Ovary is one-chambered but it becomes two-chambered due to
the formation of the false septum, e.g., mustard and Argemone. When the ovules
are borne on central axis and septa are absent, as in Dianthus and Primrose the
placentation is called free central.
4.Basal: In basal placentation, the placenta develops at the base of ovary and a
single ovule is attached to it, as in sunflower, marigold.


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