Vegetative propagation : This is an asexual method of reproduction in plants where vegetative parts namely root, stem and leaves give rise to new plants.
Vegetative propagation is of two types :
(A) Natural vegetative propagation
(B) Artificial vegetative propagation.
(A) Natural vegetative propagation :
Plant reproduce without the help of human beings.
By leaves : Leaves of some plants produce adventitious buds on their margin. Thus buds develop into new plants e.g. Bryophyllum, Kalanchoe.
By stem : In many plants, underground stems produce aerial shoots annually under favourable conditions. e.g. Potato, Zinger, Onion, Grass.
By roots : Roots produce adventitious buds which develop into new plants. e.g sweet potato.
(B) Artificial vegetative propagation :
To prepare plants with desirable characters.
These are of four types:
(i) Cutting :
In this method, small part of a plant is cut and buried partly in the moist soil then the cutting develops roots and grows into a new plant. e.g. Rose, Sugarcane, Potato, Cactus.
(ii) Grafting :
Two plants of closely related varieties are joined together so that they live as one plant.
The plant of which roots remain in the soil is called as stock.
Cutting part of a plant that is grafted on the other rooted plant is called scion.
e.g. Mango, Apple, Lemon.
(iii) Layering :
In this method, a branch of the parent plant is buried in the soil.
The portion of the branch which is connected with the soil produces roots and this rooted branch is called layer.
Layer is then detached from the parent plant and act as a new plant. e.g. Jasmine, Hibiscus.
(iv) Tissue culture or micro-propagation:
Cells or tissues which are isolated from the growing tip of plant is called explant.
The explant develops into undifferentiated mass of cells called callus in the proper culture medium.
The callus is transferred to another medium containing hormones for growth and differentiation, that forms plantlet.
These plantlets are transplanted into pot or soil to form a mature plant.
This technique is known as micro-propagation. e.g. Orchids, Chrysanthemum.
Advantages of vegetative propagation:
It is a rapid, cheap and easy method of reproduction for the multiplication of plants.
Disease free plants can be produced.
Superior quality fruits or flowers can be produced by grafting.
Genetically identical plants are produced.
Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from the seeds.
In fission the organism have lost their parental identity while in budding they have maintained their identity.
Grafting is not possible in monocot plants.
Cambium activity is essential for the union of stock and scion.
Tissue culture is also called micro-propagation because a large number of plants are formed from a small tissue.
Virus free plants are produced by micro-propagation.
(2) Sexual reproduction :-
It is a type of reproduction in which two different sexes (male and female) are involved. It involves the fusion of gametes from two different parents and results in the formation of new organism, which is genetically different from the parent.
|Difference between Asexual And Sexual Reproduction|
|S.No.||Features||Asexual Reproduction||Sexual Reproduction|
|1||Number of parents involved||One||Two|
|2||Resemblance with parents||Organisms produced resemble exactly with the parent.||Organisms do not resemble exactly with the parent but resemble in certain features with both the parents.|
|3||Type of cell division||Amitotic/mitotic||Mitotic and meiotic both are present.|
|4||Time duration for multiplication||Take less time.||Takes more time.|
|5||Variations||Variations are absent||variations are present|
|6||Adaptability||Organisms produced have less adaptability.||Organisms produced have more adaptability.|
|7||Examples||Fission, budding, vegetative propagation.||Human beings, higher plants|
Sexual reproduction in flowering plants
Sexual reproduction takes place through the agency of flowers in angiosperms (flowering plants).
Flower is a specialized condensed reproductive shoot of flowering plants on which the essential reproductive parts are inserted.
A typical flower has four whorls arranged on the thalamus.
It is the outermost whorl consisting of sepals.
Sepals are green and leaf like structure.
Calyx protect the flower bud before it opens.
It is the second whorl, inner to calyx, consisting of petals.
Petals are generally large, coloured and showy.
Corolla attracts insects for pollination.
It is the third whorl, inner to corolla, consisting of male reproductive parts called stamens.
Each stamen has two parts: Filament and anther.
Anther is a lobed structure present at the tip of filament. Each anther has pollen sacs (microsporangia) which contains pollen grains (microspores).
Each pollen grain produces two male gametes/male germ cells.
It is the fourth and innermost whorl consisting of carpels.
Carpel is present in the centre of flower.
Each carpel has three parts: Ovary, Style and Stigma.
Ovary is a swollen basal part of carpel. It contains ovules which are attached to placenta.
Each ovule contains an embryo sac that bears a haploid egg (female gamete).
Style is the middle part of the carpel. It has stigma above it and ovary below it.
Stigma is the apical part of carpel. It receives pollen grains.
Perianth :- If both sepals and petals are coloured and cannot be distinguished from each other, then their whorl is known as perianth.
Calyx and corolla are non-essential parts of the flower because they are not directly involved in reproduction.
Bisexual flower :- When the male and female reproductive parts are present in the same flower, they are called bisexual flowers e.g. Hibiscus, Mustard.
Unisexual flower :- When the male and female reproductive parts are present in different flowers, they are called unisexual flowers. e.g. : Papaya, Date palm, Mulberry, Gourd, Water melon.
Process in which pollen grains are transferred from the riped anther to the stigma. It is of two types :
(i) Self pollination :- It is the transfer of pollen grains from an anther to the stigma of the same plant. If it is in the same flower it is called autogamy (e.g. Pea) and if it is between flowers of the same plant then it is called geitnogamy (e.g. Oxalis).
(ii) Cross pollination :- It is the transfer of pollen grains from anther to the stigma of different plants of the same species (e.g. Mango).
Agencies of pollination :- Transfer of pollen grains from one flower to another is achieved by agents like wind, water, animals, insects and birds.
Significance of bright colour of flower:- The bright colour of flowers is meant to attract insects which help in pollination. White colour shines in dark which attracts insects at night. Similarly, bright colour day-blooming flowers attract insects.
Fertilization is the process of fusion of the male and female gametes, which takes place in the embryo sac present in the ovule.
After pollination, pollen grains germinate on the stigma by producing pollen tube.
The nucleus in the pollen tube divides into two male gametes.
Pollen tube penetrates the stigma and passes through the style and enters the ovule through micropyle.
It releases two male gametes in embryo sac.
One male gamete fuses with egg cell and second male gamete fuses with the two polar nuclei.
One male gamete + Egg cell Zygote.
Second male gamete + Two polar nuclei Triploid nucleus (Primary Endosperm Nucleus)
Syngamy + Triple fusion = Double fertilization.
Post fertilization changes in the flower:
Sepals, petals and stamen withers off.
Style and stigma degenerates.
Ovary develops into fruit.
Ovule grows into seed.
The seed contains the future plant or embryo which develops into a seedling under appropriate conditions.
Endospermic seed : If endosperm is not consumed.
Non endospermic seed :- Endosperm may be consumed.