- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
Reproduction is defined as a biological process in which an organism gives rise to young ones (offspring) similar to itself.
The offspring grow, mature and in turn produce new offspring. Thus, there is a cycle of birth, growth and death.
Reproduction enables the continuity of the species, generation after generation. You will study later in Chapter (Principles of Inheritance and Variation) how genetic variation is created and inherited during reproduction.
There is a large diversity in the biological world and each organism has evolved its own mechanism to multiply and produce offspring.
Habitat and internal physiology of organism and several other factors are collectively responsible for how it reproduces.
There are two types of reproduction:
(1) Asexual reproduction
(i) Offspring is produced by a single parent with or without the involvement of gamete formation.
(ii) Gametic fusion is absent.
(2) Sexual reproduction
(i) Offspring is produced by two parents (opposite sex) with the involvement of gamete formation.
(ii) Gametic fusion is present (fertilization/syngamy).
- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
A single individual (parent) is capable of producing offsprings in asexual type of reproduction. As a result, the offsprings
produced are exact copies of each other and their parents. Such morphologically and genetically similar individuals are
It is common among single-celled organisms, plants and animals with relatively simple organisation.
It is also called somatogenic reproduction because propagules are formed from somatic cells of the parent.
It occurs by fission, budding, sporulation, fragmentation, regeneration and vegetative reproduction.
(a) Binary Fission
In this process, the parent organism divides into two halves, each half forming an independent daughter organism.
It means, the parent body as a whole forms the reproductive unit and the parent continues living as two daughter
Therefore, the organisms that undergo binary fission are said to be immortal.
(ii) It occurs in Bacteria (Moneran), Amoeba and Paramecium (Protists).
Depending upon the plane of division, binary fission is of the following types:
(i) Simple Binary Fission (Irregular Binary Fission) : Division can occur through any plane, e.g.; Amoeba.
(ii) Longitudinal Binary Fission : The plane of fission passes along the longitudinal axis of the organism, e.g., Euglena.
(iii) Transverse Binary Fission : The plane of this division runs along the transverse axis of the individual, e.g., Bacteria,
In yeast, the division is unequal and a small bud (protuberance) is produced that remains attached initially to the
parent cell, later on the bud gets separated and mature into new yeast (cells).
Budding or sporulation is also shown by oidia of Rhizopus.
Buds are also reported in hydra.
(c) Spores: Members of the kingdom fungi and simple plants such as algae reproduce through special asexual
reproductive structure. The most commonly produced structures are conidia and zoospores.
(i) These are motile and flagellated spores produced inside the zoosporangia under favourable conditions.
(ii) In Chlamydomonas(n), the protoplast of cell divides to form 8-16 zoospores. They are pyramid shaped and anteriorly
biflagellated, resembling the parent cell. The parent cell wall breaks and the zoospores are liberated in water. They enlarge
and behave as adult individuals.
(iii) Zoospores are also produced in the asexual life cycle of Achlya, Saprolegnia, Phytophthora and Ulothrix.
(iv) Zoospores of Cladophora glomerata are diploid.
(i) In Penicillium, these spores are produced at the tips of special hyphal branches, called conidiophores.
(ii) There are two types of conidiophores :
(iii) The branches of conidiophores are called rami and branches of rami are called metulae. Each metula bears 2-6 flask shaped structures called sterigmata (phialides). Each sterigma produces a chain of conidia.
(iv) Features of Conidia:
b. Uni or multinucleated
c. The conidia in the chain are arranged in basipetal manner.
(d) Vegetative Reproduction
(i) Vegetative reproduction does not involve meiosis and fusion of gametes, therefore it is considered ' as a type of
asexual reproduction .
(ii) New plants or individuals are produced from vegetative parts of plants and newly formed individuals are genetically
identical to the parent plant.
(iii) It is common method of reproduction in the flowering plants.
There are two types of vegetative reproduction.
I. Natural Methods of Vegetative Reproduction:
These are methods of plant multiplication occurring naturally in which a somatic part of the plant detaches from the
body of the mother and develops into a new independent plant under suitable environmental conditions.
The detachable somatic part that functions in vegetative propagation is called vegetative propagule.
It carries one or more buds. Natural buds occur over the nodes of the stem. When placed in contact with damp soil,
the buds sprout, producing roots and new plants.
This potential is exploited by farmers, e.g., tubers of potato, rhizome of banana and ginger, bulbs, runners, offsets,
stolons, aerial stems etc.
Some propagules carry adventitious buds, e.g., normal and storage roots, leaves.
It occurs by following means:
Different types of underground stems like tuber, Germinating rhizome, bulb and corm can take part in Young shoot
A portion of underground stem bearing bud Roots forms a new plant.
(i) Tuber : It is terminal portion of underground stem branch which is swollen on account of accumulation of food.
e.g., Potato, Artichoke
(ii) Rhizome: It grows obliquely or horizontally under soil surface. It is well branched and bears nodes, internodes,
buds and scale leaves. e.g., Banana, Turmeric, Aspidium, Adiantum, Ginger
(iii) Bulb: Stem is unbranched, highly reduced and disc shaped. The bud is surrounded by many concentric scale leaves.
Leaf bases of inner ones are fleshy and edible and outer ones are dry known as tunic. e.g., Onion, Garlic, Narcissus
(iv) Corm: It grows vertically beneath the soil surface. It bears nodes, internodes, buds and scale leaves. e.g.,
Colocasia, Gladiolus, Freesia., Crocus, Amorphophallus
(3) Creeping stems:
(i) Runner: It is elongated, prostrate, sub-aerial branch with long internodes and roots at nodes. e.g., Grasses
(ii) Offset: Short horizontal branch which is one internode long and produces a cluster of leaves above and the cluster
of roots below is called offset. e.g., Eichhornia (Water hyacinth), Pistia.
Water hyacinth or 'terror of Bengal' was introduced in Bengal because of its beautiful flowers and shape of leaves.
However, it turned out to be highly invasive aquatic weed that not only spread to all water bodies of Bengal but also
throughout India. It drains oxygen from the water, which leads to death of fishes and other animals. It is very
difficult to get rid off them since it can propagate vegetatively by offset at a phenomenal rate and spread all over the
water body in a short period of time.
(iii) Stolon : It is subterranean long lateral branch arising from base of stem. It first grows obliquely upward and then
bends down to the ground surface.
e.g., Strawberry, Vallisneria Leaflets
(iv) Sucker : It arises by axillary bud of underground part of stem. This lateral branch creeps below the soil surface,
grows obliquely upward and produces new shoot.
e.g., Chrysanthemum, Pineapple, Banana
(4) Aerial shoots : Each segment of stem having at least one node can form a new plant.
e.g., Sugarcane, Opuntia
(5) Leaves: Leaves of several plants having adventitious buds help in vegetative reproduction. In Bryophyllum
adventitious buds arise from the notches present at margins of leaves.
e.g., Adiantum (walking fern), Begonia, Streptocarpus, Saintpaulia and Kalanchoe.
(6) Bulbils: These are fleshy buds which produce new plant. e.g., Agave, Oxalis, Ananas, Dioscorea, Lily, Chlorophytum
(7) Turions : Fleshy buds in aquatic plants helping in perennation, e.g., Potamogeton, Utricularia.
(i) Both tap roots and adventitious roots takes part in vegetative reproduction due to the presence of bud, known as radicle
(ii) Adventitious buds on root detaches and gives rise to new plant.
- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
Sexual reproduction involves formation and fusion of gametes to form the zygote which develops to form the new organism.
1. Two fusion gametes can be produced by same individual or different individuals. So it can be both uniparental as well as biparental (mostly).
2. Offsprings produced are not identical to parents or amongst themselves.
3. It involves meiosis and syngamy.
4. It is a slow, elaborate or complex process. So multiplication is not so rapid.
All organisms have to reach a certain stage of growth and maturity in their life cycle before they reproduce sexually. For understanding this better lets study the different phases in the life cycle of organism.
Table: Differences between Asexual and Sexual Reproduction
Phases in Life Cycle
Three phases are there in the organism's life cycle.
1. Juvenile phase
2. Reproductive phase
3. Senescent phase
1. Juvenile phase/pre-reproductive phase
During this phase organism will show growth so that it can attain certain maturity to perform the sexual reproduction.
This phase is known as vegetative phase in plants. It is of variable durations in different organisms.
2. Reproductive phase
Reproductive organs develop and mature during this phase. In the higher plants, end of juvenile phase or onset of reproductive phase is easily marked.
In the higher plants during this phase, there is formation of reproductive structures i.e., flowers.
The motto of this phase is to produce the offsprings which may be similar or dissimilar to parental generation. This phase is also of variable durations in different organisms.
Based upon flowering and fruiting pattern there are two types of flowering plants, i.e., monocarpic and polycarpic.
Monocarpic Plants :
They are plants which flower only once in their life. After flowering, they produce fruits and die. All annuals (e.g., Wheat, Rice, Marigold) and biennial plants (e.g., Radish, Carrot, Henbane), are monocarpic.
A few perennial plants are also monocarpic. Certain bamboo species (e.g., Bambusa tulda, Meloeanna bambusoides) live vegetatively for 50-100 years, flower and fruit abundantly and then die.
Strobilanthus kunthiana (vern. Neelakurinji) flowers once in 12 years.
The last time it flowered was September-October 2006. The flowering converted large hilly tracts of Kerala, Karnataka and Tamil Nadu into blue stretches that attracted a large number of tourists.
Polycarpic Plants :
They are perennial plants which after reaching maturity, flower repeatedly at intervals, e.g., Mango, Apple, Jackfruit, Grape vine, Orange.
Very few perennial plants bear flowers throughout the year, e.g., China rose (Shoe Flower). The period between two flowering phases is called Inter flowering period which is used for building up resources and is, therefore, a recovery phase. It is not the juvenile phase but is part of the mature phase.
3. Senescent Phase:
It is a post-reproductive phase. It involves structural and functional deterioration of body by accumulation of waste metabolites which ultimately leads to death.
In both plants and animals, hormones are responsible for the transitions between three phases. Interaction between hormones and certain environmental factors regulate the reproductive processes and the associated behavioural expressions of organisms.
The females of placental mammals exhibit cyclical changes in the activities of ovaries and accessory ducts as well as hormones during the reproductive phase.
In non-primate mammals like cows, sheep, rats, deers, dogs, tiger, etc., such cyclical changes during reproduction are called oestrus cycle.
Where as in primates (monkeys, apes, and humans) it is called menstrual cycle.
Many mammals, especially those living in natural, wild conditions exhibit such cycles only during favourable seasons in their reproductive phase and are therefore called seasonal breeders.
Many other mammals are reproductively active throughout their reproductive phase and hence are called continuous breeders.
- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- ACME SMART PUBLICATION
- CBSE Class 12
EVENTS IN SEXUAL REPRODUCTION
After attainment of maturity, all sexually reproducing organisms exhibit events and processes that have remarkable fundamental similarity, even though the structures associated with sexual reproduction are indeed very different.
These sequential events may be grouped into three distinct stages, namely, the pre-fertilisation, fertilisation and the post-fertilisation events.
1. Pre-fertilization events
These are events in sexual reproduction which occur prior to the process of fertilization. The two main prefertilization events are gametogenesis and gamete transfer.
(a) Gametogenesis: It refers to the process of formation of gametes-male and female.
Categories of Gametes :
(i) Isogametes : When the fusing gametes are morphologically similar they are known as isogametes or homogametes.
e.g., (i) Algae: Chlamydomonas debaryana, Ulothrix
(ii) Fungi : Synehytrium, Rhizopus
(ii) Heterogametes: When the fusing gametes are morphologically distinct types, they are known as heterogametes. It is the feature of majority of sexually reproducing organisms.
e.g., (i) Algae: Volvox, Chara, Fucus
(ii) All Bryophytes, Pteridophytes, Gymnosperms and Angiosperms.
In such organisms, male gamete is called antherozoid or sperm and the female gamete is called egg or ovum.
Sexuality in organisms:
Sexual reproduction in organisms generally involves the fusion of gametes from two different individuals. But this is not always true.
Plants may have both male and female reproductive structures in the same plant (bisexual) or on different plants (unisexual).
In several fungi and plants, terms such as homothallic and monoecious are used to denote the bisexual condition and heterothallic and dioecious are the terms used to describe unisexual condition.
A. Sexuality in animals
The individuals of all species either male or female (unisexual)?
Or are there species which possess both the reproductive organs (bisexual)?
You probably can make a list of several unisexual animal species.
Earthworms, sponge, tapeworm and leech, typical examples of bisexual animals that possess both male and female reproductive organs, are hermaphrodites.
Cockroach is an example of a unisexual species.
Table: Chromosome numbers in meiocytes (diploid, 2n) and
gametes (haploid, n) of some organisms.
B. Sexuality in Plants
In most of the lower sexually reproducing organisms, two fusing gametes are morphologically similar.
If these gametes belong to the same parent then such organisms are called homothallic, e.g., fungi (Mucor mucedo). When these gametes belong to different parents then these organisms are called heterothallic.
In higher plants there is well developed sex organs and there is clear distinction between male and female sex organs.
Angiosperms possess flowers as reproductive structures. The male sex organ is called stamen and female sex organ is carpel or pistil.
If male and female sex organs occur in the same flower then these plants are called bisexual, e.g., China rose. If flowers possess only stamen or carpel then these plants are called unisexual.
When male flower (staminate) and female flower (pistillate) are present on same plant body such plants are monoecious, e.g., Acalypha, cucurbits, coconut and maize.
However, if they are present on separate plant body then these plants are known as dioecious, e.g., date palm, papaya and mulberry.
In some of the lower plants also the monoecious and dioecious condition occur. For knowing this, we will study the sexuality in Chara and Marchantia.
Sexual Reproduction in Chara and Marchantia :
The Chara is a green alga. It is oogamous. The sex organs are highly specialised. Some workers prefer to call the male sex organ as antheridium and female as oogonium, while others did not favour this terminology.
They call the male sex organ as globule and the female as nucule and this terminology is largely followed in Chara. These sex organs are exceptionally multicelled and covered by jacket.
The jacket of nucule is formed by tube cells and the jacket of globule is formed by shield cells. The nucule has a cap of 5 coronary cells.
The sex organs are borne on the adaxial surface of the short lateral branch almost on each node. The nucule occupies an upper position than the globule.
While most of the species of Chara are monoecious, C. wallichii is dioecious. The globule matures prior to nucule (protandrous condition).
Each antheridium produces many band shaped, spirally coiled, biflagellate antherozoids. The oogonium contains a single egg. The egg is laden with starch and oil globules.
In Marchantia, the archegonia are borne on special branches called archegoniophores or the female receptacles. The archegonia may be stalked or sessile.
Cell division during gamete formation
Gametes are haploid though the parent plant body producing these gametes may be either haploid or diploid.
A haploid parent produces the gametes by mitotic division however organisms having diploid body the gametes are formed through reductional division, i.e., meiosis.
In these organisms specialised cells called meiocytes or gamete mother cells undergo meiosis. At the end of meiosis only one set of chromosomes gets incorporated into each gamete.
(b) Gamete transfer :
After the formation of male and female gametes, compatible gametes must be physically brought together to facilitate fusion (fertilisation or syngamy).
In few fungi and algae, both types of gametes are motile. In heterogametic condition, the female gamete is non motile. So there is a need of a medium through which the male gametes move.
Water is the medium for gamete transfer in algae, bryophytes and pteridophytes. A large number of the male gametes however, fail to reach the female gametes.
To compensate this loss of gametes, the number of male gametes produced in several thousand times the number of female gametes produced.
In seed plants, pollen grains are the carrier of male gametes and ovule has the egg.
The most vital event of sexual reproduction is the fusion of gametes. This process is called syngamy or fertilisation which results in the formation of a diploid zygote.
Syngamy can occur in external medium as well as inside the body of organism.
On this basis syngamy can be distinguished into two types :
(a) External fertilisation :
Syngamy occurs outside the body of organism in external medium (water). It is shown by majority of aquatic organisms like most of algae, fishes as well as amphibians.
Organisms exhibiting external fertilisation show great synchrony between the sexes and release a large number of gametes into the surrounding medium in order to enhance the chances of syngamy.
The disadvantage associated with it is that the offsprings are extremely vulnerable to predators.
(b) Internal fertilisation:
Syngamy occurs Inside the body of organisms. It is present in majority of plants like bryophytes, pteridophytes, gymnosperms and angiosperms.
It occurs in few algae like Spirogyra. In all these organisms egg is formed inside the female body where syngamy occurs.
The male gamete is motile and has to reach the egg in order to fuse it. In order to enhance the chances of syngamy large number of sperms are produced in these organisms and to compensate for this there is significant reduction in number of eggs produced.
Sexual reproduction is divided into two types.
It is a type of sexual reproduction in which transfer of male gamete occurs through the medium i.e., water. It occurs in several simple plants like algae, bryophytes and pteridophytes.
It is a type of sexual reproduction in which male gamete carrier is pollen grain and transfer of male gamete occurs through pollen tube. It is the feature of seeded plants like gymnosperms and angiosperms. Pollen grains are produced in anthers, therefore have to be transferred to the stigma before it can lead to fertilisation.
External and internal fertilisation should not be confused with exogamy and endogamy.
Exogamy: Two fusing gametes belong to different individuals. Also known as cross fertilisation.
Endogamy: Two fusing gametes belong to same individual. Also known as self-fertilisation.
3. POST-FERTILISATION EVENTS
Events in sexual reproduction after the formation of zygote are called post-fertilisation events.
It is the first cell of the new generation in all sexually reproducing organisms. Zygote is always diploid.
It is formed in the external aquatic medium in those organisms which perform external fertilization. Zygote is produced inside the body in cases where fertilization is internal.
Zygote is a vital link between two successive generations. It ensures the continuity of race from generation to generation.
The body of all multicellular organisms develops from the single-celled zygote. All the cells of the body, therefore, contain the same genetic traits as present in the zygote.
A. In Plants :
Embryogenesis is the process of development of embryo from zygote. Embryo is a multicellular stage in the life cycle of a plant or animal prior to formation of an independent individual.
In embryogenesis, the zygote undergoes repeated cell divisions through mitosis. The divisions help in growth of the embryo.
Cells undergo differentiation attaining specific shape, size and function. Cell differentiation occurs at specific locations resulting in production of different tissues, organs and organ systems.
Development of different external and internal structures is called morphogenesis. In flowering plants, zygote develops into embryo.
The food for development of embryo comes from a special tissue known as endosperm. Ultimately, the fertilized ovule matures into a seed.
A number of seeds develop in an ovary depending upon the number of ovules. Meanwhile, wall of the ovary also proliferates. It produces pericarp. The pericarp can be dry or fleshy.
The ripened ovary with pericarp and seeds is called fruit. As the fruit begins to develop, sepals, petals, stamens, style and stigma normally sheds. After dispersal, the seeds, upon reaching suitable substratum germinate and form new plants.
B. In Animals :
Animals are categorised into oviparous and viviparous based on whether the development of the zygote take place outside the body of the female parent or inside.
Whether they lay fertilised/unfertilised eggs or give birth to young ones.
In oviparous animals like reptiles and birds, the fertilised eggs covered by hard calcareous shell are laid in a safe place in the environment; after a period of incubation young ones hatch out.
On the other hand, in viviparous animals (majority of mammals including human beings), the zygote develops into a young one inside the body of the female organism.
After attaining a certain stage of growth, the young ones are delivered out of the body of the female organism.
Because of proper embryonic care and protection, the chances of survival of young ones is greater in viviparous organisms.
II. Artificial Methods of Vegetative Reproduction:
Artificial methods are man-made special techniques in which, part of somatic body of a plant is made to develop into new independent plant.
Artificial methods are used to propagate desired varieties according to human requirements, Rainy and spring seasons are the best periods for vegetative propagation.
The various horticultural methods of vegetative propagation are as follows:
Cuttings are cut pieces of stem, leaves and root which are planted in nurseries in natural polarised fashion, Pre-requisite to successful cutting is induction of rooting, For this, root promoting chemicals like IBA, NAA are used,
(i) Stem Cuttings :
It is a common artificial method of plant propagation, 20-30 cm long pieces of one year old stems are cut and their lower ends are dipped in dilute auxin for several minutes before planting in the soil. The lower ends develop adventitious roots, Buds present over the exposed parts sprout and form the shoot system,
e,g., Rosa, Duranta, Citrus, Clerodendron, Thea, Bougainvillea, Croton and China rose
(ii) Leaf Cuttings: Snake plant (Sansevieria) can be propagated by leaf cuttings, Leaves are cut transversely into two or three parts and planted in vertical position in the soil. For successful leaf cutting, besides induction of rooting, formation of adventitious buds is also important.
(iii) Root Cuttings : They are long pieces of roots which are used to artificially propagate new plants, Ability to form adventitious roots and adventitious buds are pre-requisites. Root cuttings are used in propagation of Lemon, Tamarind, Blackberry and Raspberry.
(i) It is a type of rooting-cutting method in which adventitious roots are induced to develop on a soft stem while it is still attached to the plant.
(ii) It is carried out on one year old basal shoot branches commonly during early spring or early rainy season.
(iii) A soft basal branch is defoliated in the middle where a small injury or cut is also given, like tongueing (oblique cut), notching (V-shaped cut), ringing (removal of a ring of bark). The injured defoliated part is pegged in the soil to develop adventitious roots. The pegged down branch of the plant is called layer. Later on as the roots develop, the layer is separated and planted.
(iv) Layering is of following types:
(a) Tip Layering : A shoot is bent down in the soil in such a way that its basal end is slanting while the tip is upright. Soil is pressed. It induces root formation and later growth of shoot tip.
e.g., Blackberry, Raspberry.
(b) Trench Layering : The basal branch is pegged in a horizontal position in a trench made in soil. It develops a number of vertical shoots. e.g., Walnut, Mulberry.
(c) Serpentine Layering : The basal branch is pegged at several places in soil at regular intervals, so as to form many plants. e.g., Clematis
(d) Mound (Stool) Layering
The shoot is pruned and its lower part is covered by soil but the tip is kept outside the soil. When a number of new shoots develop, soil and saw dust are poured over the base to form a mound. Each shoot develops roots. Rooted shoots are separated and planted.
e.g., Currant, Gooseberry, Apple, Pear and Jasmine
(e) Gootee (Air Layering)
(i) It is an ancient horticultural technique for propagation of tropical and subtropical trees and shrubs where soft branches do not occur near the soil.
(ii) During early monsoon rains, 3-5 cm long ring of bark is removed from the basal region of a healthy and woody branch. It is covered by a thick plaster of grafting clay. Grafting clay is made of 1 part cow dung, 1 part finely cut hay or moss and two parts clay. To it is added water and a small quantity of root promoting hormones like IAA, IBA or NAA. It is then wrapped in polythene. After 2-3 months, roots appear. The shoot is now cut below the covered part and used for planting.
e.g., Litchi, Pomegranate.
(i) Grafting is a technique of connecting two parts, usually a root system and a shoot system of two different plants in such a way that they unite and later develop as a composite plant.
(ii) It is used only in cambium containing eustelic plants.
(iii) A small shoot of plant with superior traits is employed. It is called graft or scion. It should have one to several buds. The root system of the other plant is allowed to remain intact. It is called stock (under stock). The shoot of the stock is often cut 10-30 cm above the base of the root. Leaves and buds present over the stump of stock are removed.
(iv) In grafting, scion is fixed over the stock in a manner that cambia of the two come in contact. The union is covered with grafting wax. It is then tied with the help of a bandage, tape, rubber or nail. The buds of the stock are not allowed to sprout.
They are removed as soon as they are noticed.
e.g., Mango, Apple, Pear, Citrus, Guava, Plum, Peach, Pine etc.
The various types of grafting are as follows:
(a) Tongue (Slice or Whip) Grafting
Oblique sloping cut or notch is given to both stock and scion. The two perfectly fit upon one another. They are tied together.
(b) Wedge Grafting
V-shaped notch is given to stock while wedge like cut is given to scion.
(c) Crown Grafting
Many scions are selected and shaped at the base to form wedge. Many slits are formed on the sides of stock. Scions are inserted in the slits and are bandaged.
(d) Approach Grafting
Two independently growing plants are brought together. The shoots of the two are given cuts at the same level for a distance of 2.5 -5.0 cm. The cuts are in the form of smooth slices of bark, tongue shaped cuts or deeper vertical cuts. In this grafting, the scion is cut below the graft while stock is cut above the graft after the establishment of union.
(e) Bud Grafting
Scion is a bud with a small piece of bark and cambium. Stock is given a T-shaped cut. Bark is lifted to expose cambium. Bud is inserted and the bark is allowed to come back to its original position. Only the bud is exposed. The joint is treated with grafting wax and bandaged. Bud sprouts after 3-5 weeks. Bud grafting is commonly practised in apple, peach and rose.
Micropropagation is the raising of new plants from a small plant tissue with the help of tissue culture technique.
Tissue culture is the technique of maintaining and growing cells, tissues, etc. and their differentiation on artificial medium under aseptic conditions inside suitable containers.
N.Grew first pointed out that flowers are reproductive organs of plants.
Largest male gamete is seen in Cycas.
Citric acid helps in attraction of male gametes towards the archegonium in Lycopodium, a pteridophyte.
Parthenospores: A spore is formed directly from a gamete. It is also called azygospore.
Parthenogamy : It is the union of two incompatible gametes like two female gametes.
Parthenoapogamy: It is the fusion of vegetative nuclei.
Parthenocarpy (Noll, 1902) : It is formation of fruits without fertilization. It is useless in case of plants where seeds provide the economic produce, e.g., Almond , Walnut, Coconut, Pomegranate.