Reproduction in Organisms

All organisms can live on earth for a particular time period. The period from birth to the natural death of an organism represents its life span. Life span of organisms varies from few days to thousands of years and organism to organism.
OrganismsLife Span
Elephant70-80 years
Rose15 years
Dog 15-20 years
Butterfly1-2 weeks
Crow15 years
Banana Tree 15 years
Cow22 years
Parrot140 years
Crocodile60 years
Horse30-40 years
Fruit fly 20-30 years
Rice plant4-5 months
Tortoise100-150 years
Banyan Tree More than 200 years
 Crow and parrot are of almost equal size, but crow has a life span of only 15 years while parrots can live for 40 to more than 100 years (depending on species). Similarly mango tree lives for 200 years while Peepal tree (Ficus religiosa) has a life span of about 2500 years. Whatever may be the life span of organism, death of all organisms are sure. Means no organism is immortal or living for ever. All living organisms are mortal. No individual is immortal except single celled organisms.In single celled organism like amoeba they grow up, and then they undergo cell division, that means the matured mother cell divides to produce two daughter cells. There neither the organism, nor the body part is dying.So in these cases organism is considered as immortal. During the life span ,an organism attains maturity and it reproduces to create its next generation which is commonly called as reproduction. Reproduction: 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 species generation after generation. Each organism has evolved its own mechanism to multiply and produce offspring. ● The organism's habitat, its internal physiology and several other factors are collectively responsible for reproduction. Basic Features of Reproduction 1. Duplication of cellular apparatus: All cellular apparatus must be duplicated before cell division. This makes the equal distribution of cellular material among daughter nuclei. During this time replication of chromosome present in the chromosome takes place.● 2. Formation of reproductive units 3. Cell division Types of Reproduction: There are two types of reproduction: asexual and sexual reproduction. Though asexual reproduction is faster and more energy efficient, sexual reproduction better promotes genetic diversity through new combinations of alleles during meiosis and fertilization. However, both of these types of reproduction can be beneficial to different organisms. 1. Asexual Reproduction: The offspring is produced by a single parent without the involvement of gamete reproduction. 2. Sexual Reproduction: Two parents (opposite sex) participate in the reproductive process and also involve fusion of male and female gametes. Asexual Reproduction ● Off springs are produced by single parent or individual. ● It’s simple and fast method of reproduction. ● Clones: offsprings that are produced by asexual reproduction are genetically and morphologically identical to one another and also exact copies of their parents, hence they are called clones. ● The offspring produced inherits all character from the parent because; it is getting one set of chromosome from the parental organism through mitotic division. ● Asexual reproduction is common among single celled organisms, and in plants animals with relatively simple organizations. ● It is with or without gametes. But fusion of gametes is absent. Modes of Asexual Reproduction1. Cell division2. Binary fission3. Sporulation4. Budding 5. Fragmentation 6. Vegetative propagation in plants Cell division: In protists and Monerans, cell division is itself a Mode of reproduction, i.e., parent cell divides into two cells to give rise to new individuals.
Binary fission: Single celled organisms like Amoeba, paramecium etc., reproduces by binary fission, where a cell divides into two halves and each rapidly grows into adult. The mechanism in this process is, the body of parental organism whole forms a reproductive unit. That divides in to two halves. That means Karyokinesis (nuclear division) is followed by the cytokinesis (Cytoplasmic division). Binary fission is of different types, based on the plane of division a) Simple binary fission: in this type, the division can occur through any plane. Eg: amoeba b) Transverse binary fission: in this type the division can occur through the transverse axis of the organism. Eg: Diatoms, Paramoecium ,Bacteria c) Longitudinal binary fission: In this the division can occur through the longitudinal axis of organism. Eg: Euglena * Encystation: The phenomenon where the Amoeba withdraws its pseudopodia and secretes three-layered hard covering or cyst around itself during unfavourable conditions. * Spore formation: On the onset of favourable conditions the encysted amoeba divides by multiple fission and produces many minute amoeba or pseudopodiospores. Later the cyst wall bursts out releasing spores to the surrounding medium to grow up into many amoebae. * Budding: The division is unequal and cells produce small buds that remain attached initially to the parent cell which,eventually gets separated and matures into new organisms. Eg – Yeast *Sporulation: Members of kingdom Fungi and simple plants like algae reproduce through specialized asexual reproductive structures. The most common of these structures are Zoospores, and Conidia which are usually microscopic and motile. Zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Zoospore is endogenous because it is produced inside sporangia. Conidia are non-motile exogenous asexual reproductive spore of fungi that develop through abstriction on special spore-producing structures called conidiophores. The spores detach when mature. They vary widely in shape, colour, and size, large ones being called macroconidia, small ones, and microconidia. It is found in members of Actinomycetes. For example, Penicillium,Aspergillus. In hydra, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and, when fully mature, detach from the parent body and become new independent individuals. Gemmules are internal buds found in sponges and are involved in asexual reproduction. It is an asexually reproduced mass of cells that is capable of developing into a new organism. They are small bud-like cells, which are formed by sponges to withstand unfavourable environmental conditions. The internal buds, gemmules are resistant to dehydration, freezing and can survive even without an oxygen supply. The outer layer of the gemmule is enclosed and protected with the endospore that is surrounded by a layer of spicules, which helps the gemmule from all other unfavourable environmental conditions and also helps gemmules in growing into an adult freshwatersponge. ● Fragmentation: Fragmentation refers to the process by which a living organism split into parts that later grow identical to the original organism. Each of the formed fragments after going through the cycle of growth develops into a mature, fully-grown individual that is identical to its parent with respect to shape, size, and other dimensions. Fragmentation is found in both animals and plants. Fungi, lichens, molds, worms, sea stars, acoel flatworms, and sponges are some of the common examples where the mode of reproduction occurs via fragmentation. Planaria reproduce both sexually and asexually. There are two methods of asexual reproduction: fragmentation and spontaneous “dropping tails”. Fragmentation usually begins with a transverse constriction just behind the pharynx, which increases until the two parts separate and move away from each other. The asexual reproduction in Spirogyra is s fragmentation. In this method, the body of spirogyra when matures and will get break into many smaller pieces or fragments due to strong water current. Then each piece will later grow into new individuals. ● Vegetative propagation in plants: Any form of asexual reproduction occurring in plants in which a new plant grows from a fragment of the parent plant or grows from a specialized reproductive structure (such as a stolon, rhizome, tuber, corm, or bulb) under favourable conditions. The detachable part which is involved in vegetative propagation is called vegetative propagules. Vegetative reproduction is an asexual method of reproduction as it does not involve male and female parents and their sex cells or the fusion of gametes. There are two types of vegetative reproduction A. Natural methods of vegetative reproduction. B. Artificial or horticultural method of vegetative reproduction. A: Natural methods of vegetative reproduction. Natural vegetative reproduction is the growth and development of plants without any human interference. Natural vegetative propagation can be enabled by the development of adventitious roots. Formation of newplants from the roots, stem and leaves of the parent plant is coming under natural method. A plant body have different parts. They are the root, which helps in anchoring plants and absorbing water and nutrients from soil. Stem is a part of shoot system which helps in the conduction of water and nutrients to different parts of plant body. Leaf is the plant part that helps in photosynthesis which is most important. In some plants the stem gets modified to perform some other functions like storage of food, support, protection and vegetative propagation. They are commonly called as modified stem. Based on the type of modification, stem modification can be classified in to, a) Underground modifications b) Sub Arial modifications c) Arial modifications a) Underground modifications Plants that produce underground modifications of stem are helpful for its perennation (the ability of organisms, mainly plants to survive from one germination season to another during unfavourable conditions) and storage of food. These plants produce aerial shoots annually. These underground modifications look like roots but can be distinguished with the following characteristics. ● Nodes and internodes are seen.● At the nodes the presence of scale leaves, buds, and adventitious roots are seen.● The internal structure of these modifications is similar to the aerial stem and not to a root. Some underground stem modifications are Rhizome, Bulb, Corm and Tuber. Rhizome ● It’s a fleshy underground stem.● This grows horizontally beneath the surface of the soil.● It's a non-green underground stem, with nodes and internodes. ● The nodes have dry scale leaves with axillary buds. ● Terminal buds can also be seen.● The terminal bud produces the green aerial shoot in favourable season which dies after flowering, leaving a scar on the rhizome.● The adventitious roots arise from the lower sides. ● The rhizome stem that grows obliquely is called a root-stock rhizome Examples of rootstock rhizome: Banana● When they grow horizontally they are known as straggling rhizomes. Examples of straggling rhizome: Ginger, turmeric●
Rhizome
● Bulb● It is a short underground stem.● This type of modified stem looks like a highly condensed discoid stem.● The stem is reduced to a flattened disc.● Fleshy scale leaves develop from the disc, practically enveloping it.● The upper surface has a terminal bud and there are many fleshy scaled leaves present. ● The terminal bud grows into the aerial shoot during favourable season.● At the base of the bulb, there are many adventitious roots present. ● The scale leaves are fleshy due to the storage of food matters.● These bulbs can be scaly or tunicated. ● A tunicated bulb will be covered by a sheath of dry membranous scale leaves which is called a tunic. ● Examples of tunicate bulbs: Onions and garlic.● In the case of scaly bulbs, there will be no tunic present. ● Examples of scaly bulbs: Lily.●
Bulb
Corm● It is a very fleshy stout modified stem.● This is a condensed rhizome that grows in a vertical direction.● This produces green aerial portion from the terminal bud● It has a flattening base and is more or less spherical in shape. ● It has distinct circular nodes and internodes. ● The nodes have scale leaves and axillary buds.● Scale leaves are present and daughter corms ● They are formed from the axils of the scale leaves. ● The adventitious roots are seen at the base or all over the body area. Examples: Colocasia, Crocus, Amorphophallus
Corm
 Tuber ● It is a swollen tip of an underground lateral stem.● These swollen ends of the underground branches are the tubers.● Slender branches develop from the underground part of the stem and grow more or less horizontally beneath the surface of the soil The growth Amorphophallus of the branch is arrested and the tips begin to enlarge due to accumulation of food matters.● It is covered by a Corry. ● The skin has several depressions which are known as eyes. ● Each eye is a node and bears one or more buds subtended by a leaf scar.● A big scar at one end also known as the heel end of a potato marks its attachment to a stolon.● Adventitious roots are generally absent in tubers. ● Example: Potatoes● The potato plant bears three types of stem,— first, green aerial stems; second, underground stem growing beneath surface of the soil which may be called a stolon; and third, the swollen tip—the tuber.● In potato plant slender branches develop from the underground part of the stem and grow more or less horizontally beneath the surface of the soil.● The morphology of potato and sweet potato is confusing. Potato is a modified stem and sweet potato is a modified adventitious root.●
Tuber
● ● Condensed nodes and internodes, scale leaves and eyes are clear characters to establish that potato is a modified stem. b) Sub Arial modifications Sub aerial stem found in plants with weak stem in which branches lie horizontally on the ground. These are meant for vegetative propagation. In this, stem is partially aerial and partially underground. Short aerial branches and adventitious roots develop at the nodes. If that entire branch is detaching from the node, that can develop as a separate plant. These plants are commonly called as creepers. Their sub aerial stem modification is meant for vegetative propagation. There are four types of sub aerial stem modifications. 1. Runner 2. Sucker 3. Stolon 4. Offset 1. Runner:● Runner is a creeping stem with long internodes.● This runs horizontally on the soil surface. ● An underground runner is called sobole, e.g. Agropyron.● A mother plant produces a number of runners in all directions.● The nodes bare, axillary buds, adventitious roots and scale leaves. ● Runner arises from an axillary bud.● Runners break off and grow into individual plants, and thus help in vegetative propagation. ● Examples – C-Cynodon (Lawn grass), Oxalis (Wood sorrel), Centella etc. ●
Runner
●
Agropyron
● 2. Sucker:● Sucker is another form of sub aerial stem modification.● Sucker stems rise from the basal underground part of the main stem.● Under the soil it grows horizontally for a distance and then emerges upwards. ● Before separating from the mother plant it develops a leafy shoot and adventitious roots. ● The common sucker-bearing plants are Chrysanthemum ,Musa (banana), Mint, pineapple ,strawberry
Sucker
 3. Stolon: This is a lateral branch which is weak and that arises from the base of main stem. After growing aerially for some time, it bends downwards to touch the ground. Then the terminal bud give rise to new shoot and adventitious roots. In horticultural methods, the branches are lowered down to touch the soil and their roots will get developed. When touches the ground it produces roots and becomes an independent plantlet. Eg: Jasmine, Colocasia, Vallisneria
Stolon
 4. Offset● Offset is short and thicker and found mainly in aquatic plants.● It is a short runner with one internode long. ● It originates from leaf axil, grows as a short horizontal branch.● It produces a rosette of leaves above and adventitious roots below.● This type of stem modification is generally found in aquatic plants like Pistia (water lettuce), Eichhornia (water hyacinth), and Houseleek etc.
Eichhornia
 c) Arial modifications of stem : In some plants, aerial stem, vegetative buds and floral buds may get modified to perform special functions like climbing, protection, food synthesis and vegetative propagation. This kind of aerial stem structures that undergo modifications to perform special function includes, thorns, tendrils phylloclade etc. 1. Stem tendrils
Stem tendrils
 ● Stem or the branches of stem get modified into green thread like structures called tendrils.● They are leafless structures● Tendrils are meant for climbing. ● These are mainly for plant support and attachment.● Tendrils grow in a spiral form.● Then these spiral structures stretches out and twines around any suitable support.● They may be branched or un-branched.● At the point of branching of the tendril a scale leaf is always present. Tendrils are mainly arising from the stem. So stem tendrils can be sub divided in to four. They are :( picture 1 to 5) I. Axillary tendrils: Example: Passiflora II. Extra axillary tendrils: Example: Cucurbita III. Apical bud tendrils: Also known as leaf-opposed tendrils and a common example is a grapevine IV. Floral bud tendrils: Also known as inflorescence tendrils. Example: Antigonon, cardiospermum 2. Thorns
Thorns
 ● Thorns are for protection.● These are pointed, hard or woody and straight structures.● Sometimes they may be branched, they bear leaves, flowers.● In Citrus, Duranta and Aegel thorns are modified axillary buds; ● In Carrissa terminal bud gets modified into thorn.● Thorns are used as organs of defence or climbing (e.g. Bougainvillea) ● Thorns are with vascular connections.● Thorns prevent transpiration. 3. Phylloclade
Phylloclade
● These are leaf modifications.● The leaves are modified into spines or scales● These modifications help to check transpiration.● In this kind of plants, the growth of the leaves are controlled.● Leaves won’t be present on such plants.● The main role of leaf is in photosynthesis.in these kind of plants where leaves are absent, the photosynthesis is performed by fleshy, green flattened or cylindrical branches● These branches are of unlimited growth. ● They take part in photosynthesis and store water. ● These are seen in xerophytes. ● Eg: Opuntia, Euphorbia, Casuarina, Cocoloba etc. 4. Cladode
Asparagus
 ● This is one type of phylloclade which consists of only one internode.● These are cylindrical but non fleshy.● Cladodes help in photo synthesis.● Eg; Asparagus● In this leaves are modified in to prickles. Prickles are superficial outgrowths on plants.● Cladodes develop in the axils of the scale leaves. 5. Bulbils
Phylloclade Cladode
It is the structure in which stem and also main branch terminates into leaf like flattened structure It is the structure in which only branch terminates into leaf like flattened structure
Main stem perform role in phyllocladeMain stem do not perform role in cladode
It contains both nodes and internodesIt contains only internodes
Many nodes and internodes are present. One long internode only.
True leaves are present as caducous. True leaves are present as spines.
It is present in Asparagus and Ruscus.It is present in Opuntia and euphorbia.
Phylloclade has mucilageCladodes do not have mucilage.
 ● Bulbils are a type of vegetative reproduction.● Bulbils are the modifications of vegetative or floral buds.● Eg: Dioscorea. In this plant bulbils are condensed auxiliary buds.● Bulbils are ment for storage purpose.● Vegetative buds or floral buds modify in to swellon structures and they are called bulbils. ● These bulbils may get separated from the parent plant and they give rise to a new plant. 6. Thalamus ● Flower is a specialised reproductive shoot which possesses a highly condensed axis called thalamus or torus.● It forms a broadened tip of pedicel or floral stalk. ● Nodes and internodes are not distinct.● Thalamus is supplying nutrients to flower.● Thalamus bears four types of floral organs (sepals, petals, stamens and carpels), each from their own nodes.● In certain cases the thalamus nodes become clear due to elongation of internodes between sepals and petals (anthophore, e.g., Silene), petals and stamens (androphore, e.g., Passiflora) or stamens and carpels (gynophore, e.g., Cleome).●
Thalamus
● B: Artificial methods of vegetative reproduction. Vegetative propagation or vegetative reproduction is the growth and development of a plant by asexual means. This development occurs through the fragmentation and regeneration of specialized vegetative plant parts. Many plants that reproduce asexually are also capable of sexual propagation. The Process of Vegetative Propagation● Vegetative reproduction involves vegetative or non-sexual plant structures, whereas sexual propagation is accomplished through gamete production and subsequent fertilization.● In non-vascular plants such as mosses and liverworts, vegetative reproductive structures include gemmae and spores. ● In vascular plants, vegetative reproductive structures include roots, stems, and leaves.● Vegetative propagation is made possible by meristem tissue, commonly found within stems and leaves as well as the tips of roots that contain undifferentiated cells. ● These cells actively divide by mitosis to allow widespread and rapid primary plant growth. ● Specialized, permanent plant tissue systems also originate from meristem tissue. ● It is the ability of meristem tissue to continually divide that allows for plant regeneration required by vegetative propagation.● Vegetative propagation is a form of asexual reproduction,● Plants produced through this system are genetic clones of a parent plant. This uniformity has advantages and disadvantages.● Advantages of vegetative reproduction.● One advantage of vegetative propagation is that plants with favourable traits are repeatedly reproduced. ● The plants which do not produce viable seeds are propagated by this method.● Commercial crop growers can employ artificial vegetative propagation techniques to ensure advantageous qualities in their crops.● Plants with reduced power of sexual reproduction, long dormant period of seed or poor viability are multiplied easily through this method. Disadvantages of vegetative reproduction● A major disadvantage, of vegetative propagation is that it does not allow for any degree of genetic variation. ● Plants that are genetically identical are all susceptible to the same viruses and diseases and crops produced through this method are, therefore, easily wiped out. Artificial vegetative propagation is a type of plant reproduction that involves human intervention. The most common types of artificial vegetative reproductive techniques include 1. Cutting 2. Layering 3. Grafting 4. Suckering 5. Tissue culturing (Mcropropagation) These methods are employed by many farmers and horticulturists to produce healthier crops with more desirable qualities. 1. Cutting:● A part of a plant, typically a stem or leaf, is cut off and planted.● Adventitious roots develop from the cuttings and a new plant forms.● Cuttings are sometimes treated with hormones before being planted to induce root development.● For this root promoting chemicals like IBA, NAA are used.● After placing in moist soil, it is allowed to develop roots and that may grow as a complete new plant.● Eg: Rose , Bougainvillea On the basis of plant part , which is used for cutting, and relative position on plant, cutting is classified in to ●
Cutting
● a) Stem cutting b) Leaf cutting c) Root cutting a) Stem cutting:● It’s the common artificial method of plant propagation● 20 to 30 cm long stems which are of minimum one to two years old are cut and used for this.● Then before planting in soil, the lower part of the cut stem is dipped in diluted Auxin for few minutes.● After few days, the lower ends of the cutting develop adventitious roots.● Later buds sprout and form the shoot system● The shoots with high carbohydrate content usually root better.● Broadly, there are four types of stem cuttings, namely hardwood, softwood, semi-hardwood and herbaceous cuttings.● Eg: Rose, China rose, Croton●
Stem cutting
● b) Leaf cutting● In this method, propagation of leaf bud cutting is done.● This method is used when there is a shortage of planting material.● In such shortage conditions, leaf cutting material is helpful.● Leaves are cut in to two or three parts, and planted in the vertical position in the soil or vermicompost.● For successful leaf cutting, adventitious bud and rooting will start.● During the growing season of plant leaf bud cutting preparation should be done.● If the bud is entering in to a dormant stage, it is very difficult to bring in to active stage. ● If the bud is in dormant stage, rooting won’t take place.● Eg: cactus and Begonia.●
Leaf cutting
 c) Root cutting:● Propagation by means of root cuttings is also a simple and cheap method of vegetative propagation.● This method is used in species, which are difficult-to-propagate by other methods.● In this method long pieces of roots are used for artificial propagation.● In general, the plants, which produce suckers freely, are easily propagated by root cuttings.● Eg: Blackberry and raspberry are commercially propagated by this method● The common plants which are propagated through root cutting are, Lemon and Tamarind● ● 2. Layering● Layering is a common method used for plant propagation.● This is the common asexual reproduction method in runner plants like climbing rose, jasmine, bougainvillea● Mainly used for the propagation of rose, jasmine, grape vine, lemon, rhododendrons and magnolias.● In this method roots are developed on a stem when it is still attached to the parent plant. ● The stem or branch that develops adventitious roots while still attached to the parent plant is called a layer. ● In black raspberries and trailing blackberries this is a natural means of reproduction.● Layering can be artificially induced in many plants by bending the branch to the ground and covering a medium portion of it below the soil. ● The apical portion of the branch is left exposed to the air to form the leaves.● The part below the soil develops adventitious roots. ● After root formation, the connection of the layered branch can be cut from the parent plant and grown independently.
Layering
Different types of layering area) Simple or Tongue layeringb) Compound or serpentine layeringc) Tip layeringd) Mound layeringe) Air layering a) Simple or Tongue layering:
Simple or Tongue layering
 ● In simple layering method, a low growing stem of more than one year age is bent downward and the target region is buried in the soil.● A few inches of the leafy stem must remain above the ground for the bent stem to grow into a new plant.● The buried portion of the stem develops roots after 2-3 months when watered regularly.● When the stem develops roots, it is separated from the parent plant and kept in nurseries.● Plants like lemon, citrus, climbing rose etc. are propagated by this method. b) Compound or serpentine layering:
Compound or serpentine layering
 ● This is almost similar to simple layering.● Only difference is the flexible branch which is selected for layering is covered with soil in multiple locations.● The branch is bending many times, and at each bending it is covered with soil.● Under each covering root development starts.● The advantage of this is, from the same branch, more plantlets can be made.● This method is mainly useful in the case of creepers or plants with longer branches.● This method is used for Clematis, Heart leaf philodendron, Wisteria etc. c) Tip Layering:
Tip Layering
 ● The tip of the stem of a plant is buried in the soil to develop new plants in this method.● About a 5 to 8 cm long tip of the stem is buried in the soil and watered regularly.● When the tip develops roots, the portion of the stem is separated from the parent plants after 3-4 months.● This method is commonly applied in raspberry, blackberry, etc. d)Mound layering:
Mound layering
 ● It is also called as stool layering.● Mound layering is useful with heavy-stemmed, closely branched shrubs, like Spirea, Flowering Quince, or Magnolia. ● It is also useful for fruit root stock production.● The original plant may be cut back to encourage many new shoots to grow from the base. ● Then, the following spring after the new shoots have grown approximately 8-10 inches, mound soil containing sphagnum peat moss about 7-9 inches deep around the shrub .● Roots will grow into the surrounding soil from the new growth. ● The following autumn or spring, gently dig into the mound, separate and transplant the new plants. e) Air layering (Gootee):
Air layering
 ● The target region of the stem is wounded or a strip of bark is removed and then encased in a moisture retaining medium, such as a moss or cloth.● It is further surrounded in a moisture barrier such as a plastic film.● Rooting hormone i.e. IBA (Indole -3- butyric acid), IAA, NAA is often applied to encourage the growth of roots.● The wounded portion develops roots within 4-8 weeks.● Then, the portion is separated from the parent plant and planted.● Air layering is the most popular method of artificial vegetative propagation.● Eg: Litchi, Pomegranate 4. Grafting:
Grafting
 ● Grafting is an ancient, vegetative, asexual plant propagation technique. ● It is accomplished most commonly by connecting two plant segments, the shoot piece known as ‘scion’ and the root piece called ‘rootstock’ (stock).● When more than two parts are involved, the middle piece is called the interstock.● Grafting is a union of scion stems over the stock plant.● The graft is NOT a hybrid.● Characters of stock & Scion are never mixed in flowers & fruits. ● The exhibited plant characters should always belong to Scion.● Union of internal tissues called cambium in both plants is imperative for successful grafting; when such union happens the stock and scion grow together as a single entity. ● In an ideal graft, roots & central main stem belong to stock, whereas all the growing branches, leaves, flowers & fruits belong to the scion.● Graft, in horticulture, the joining together of plant parts by means of tissue regeneration.● In modern horticulture grafting is used for a variety of purposes: to repair injured trees, to produce dwarf trees and shrubs, to strengthen plants’ resistance to certain diseases, to retain varietal characteristics, to adapt varieties to adverse soil or climatic conditions, to ensure pollination,to produce multifruited or multiflowered plants, and to propagate certain species (such as hybrid roses) that can be propagated in no other way.● Mainly this method is used to develop better variety of fruits like apple, Avocado, Mango, Citrus plant like orange, Rubber plants, Rose. Various types of Grafting are: a) Tongue (splice or whip) grafting: It is a term used in grafting of plants. For the whip and tongue graft, similar cuts are made on the stock and scion. These are made with a single draw of the knife and have a smooth surface so the two can develop a good graft union. b)Wedge graftingV- Shaped notch is given to stock while wedge like cut is given to scion. c) Crown graftingA method of grafting trees in which the base of one or (often) more scions of a small diameter are inserted under the bark around the stump of a stem or branch of much larger diameter. d)Approach graftingThe characteristic features of approach grafting are that two independent, self-sustaining plants are grafted together. After the formation of union, the top of rootstock plant is removed above the graft union and the base of the scion plant is removed below the graft union.Generally, it is performed with one or both of the plants to be grafted, which are growing in a container. Rootstock plants in containers may also be placed adjoining to an established plant, which is to furnish the scion part of the new grafted plant.It must be performed in the season when plants are in active growth because under such conditions, rapid healing of the graft-union will take place. e) Bud graftingBud grafting (also called chip budding) uses a bud instead of a twig. Grafting roses is the most common example of bud grafting. In this method a bud is removed from the parent plant, and the base of the bud is inserted beneath the bark of the stem of the stock plant from which the rest of the shoot has been cut. 5. Suckering● Suckering, Vegetative formation of a new stem and root system from an adventitious bud of a stem or root, either naturally or by human action. ● Such asexual reproduction is based on the ability of plants to regenerate tissues and parts. ● Examples of plants that spread by suckers include red raspberry, forsythia, and lilac. ● Suckering allows horticulturists and agriculturists to reproduce a desired plant over and over without significant variation. 6. Tissue culturing (Mcropropagation)● Plant tissue culture is a collection of techniques used to maintain or grow plant cells, tissues or organs under sterile conditions on a nutrient culture medium of known composition.● It is widely used to produce clones of a plant in a method known as micro propagation. ● Plant tissue culture relies on the fact that many plant cells have the ability to regenerate a whole plant (totipotency).● Single cells, plant cells without cell walls (protoplasts), pieces of leaves, stems or roots can often be used to generate a new plant on culture media given the required nutrients and plant hormones. Different techniques in plant tissue culture may offer certain advantages over traditional methods of propagation, including:★ The production of exact copies of plants that produce particularly good flowers, fruits, or have other desirable traits.★ To quickly produce mature plants.★ The production of multiples of plants in the absence of seeds or necessary pollinators to produce seeds.★ The regeneration of whole plants from plant cells that have been genetically modified.★ The production of plants in sterile containers that allows them to be moved with greatly reduced chances of transmitting diseases, pests, and pathogens.★ The production of plants from seeds that otherwise have very low chances of germinating and growing, i.e. orchids and Nepenthes.★ To clean particular plants of viral and other infections and to quickly multiply these plants as 'cleaned stock' for horticulture and agriculture. Steps in plant tissue cultureSTAGE 1: Initiation phase● The initiation phase is the first phase of tissue culture. ● Here, the tissue of interest is obtained and introduced and sterilized in order to prevent any microorganism from negatively affecting the process.● It is during this stage that the tissue is initiated in to culture. STAGE 2: Multiplication stage● The multiplication phase is the second step of tissue culture where the in vitro plant material is redivided and then introduced in to the medium. ● Here, the medium is composed of appropriate components for growth including regulators and nutrients. ● These are responsible for the proliferation of the tissue and the production of multiple shoots. STAGE 3: Root formation● It is at this phase that roots are formed. ● Here, hormones are required in order to induce rooting, and consequently complete plantlets. General procedure for plant tissue culture:Medium preparation: The appropriate mixture (such as the MS mixture) is mixed with distilled water and stirred while adding the appropriate amount of sugar and sugar mixture. Here, the pH of medium is adjusted. Agar is added to the mixture. After cooling, the warm medium is poured into polycarbonate tubes. The tubes are placed in a pressure cooker and sterilized for 20 minutes. Plant preparation: Cut the plant part in to small pieces (about 1cm across). Using detergent and water, wash the plant part for about 20 minutes. Transfer the plant part in to sterilizing Clorox solution, shake for a minute and leave to sock for 20 minutes. Gently discard the Clorox and retain the plant part in the ontainer and then cap the container. Transferring the plant material to a tissue culture medium: 70 percent alcohol should be used for the sterilization of the equipment used and containers.Using sterilized gloves, remove the plant part from the container and on to a sterile Petri dish.Using a sterile blade cut the plant material to smaller pieces of about 2 to 3 mm across avoiding the parts that have been damaged by bleach. Using sterile forceps, place a section of the plant in to the medium. Replace the lid/cap and close tightly. This procedure will result in the development of a callus, which then produces shoots after a few weeks. Once the shoots develop, then the plant section may be placed in the right environment (well lit, warmth etc.) for further growth. Sexual reproduction● The reproduction in which the gametes of two parents fuse to give rise to a zygote is called sexual reproduction.● Male and female gametes are formed either by the same individual (uniparental) or different individual (Biparental) of the opposite sex.● Because of the fusion of male and female gametes, sexual reproduction results in off springs that are not identical to the parents.● This involves fusion of gametes or syngamy The entire sexually reproductive organism has three phases in their life cycle.Phases in life cycle:Juvenile phase-● The period of growth from birth to reproductive maturity in animals is called juvenile phase ● In plants this inter flowering period is known as vegetative phase. Reproductive phase-● The phase in which the organisms reproduce sexually is called reproductive phase. Senescent phase-● The phase between reproductive maturity and death of an organism is called senescent phase, ● This is characterized by gradual deterioration in the body leading to the death of an organism. Based on the life span of plants, plants can be differentiated into 3 typesAnnual plants- live for one year and start flowering at the end of the year.Biennuals plants- live for two years and start flowering in the second year.Perennial plants- live for several years but flower only once in their life time. Example- bamboo species flower only once in 50-100 years. Strobilanthus kunthiana flowers once in 12 years. Events in sexual reproduction: Typically there are three stages of reproduction in humans, namely – pre-fertilization, fertilization, fertilization and post-fertilization. Pre-fertilization: Gametogenesis, which is the the formation of gametes and transfer of gametes are two of the main events of pre-fertilization stage. In gametogenesis, two types of gametes i.e. male and female haploid cells are formed. These morphologically distinct gametes are known as heterogametes. The male gamete is called sperm or antherozoid, and ovum or egg is the female gamete. In case of some algae, these gametes are often quite similar. This, however, makes it challenging to categorise them as male and female. Usually, these gametes are called homogametes or isogametes.
Homogametes
 Transfer of gametes: The fact female gamete is immovable makes it essential to transfer male gametes to initiate the process of fertilization. In unisexual animals, gametes are transferred through sexual intercourse whereas, in case of plants, the said transfer is facilitated through pollination. Fertilization: Fertilization is one of the most significant events in sexual reproduction and is also known as syngamy. It is a process where a male and female gametes fuse to form a diploid zygote. Typically, fertilization tends to occur either inside (internal fertilization) or outside the body of an organism (external fertilization). Notably, in certain organisms like honeybees, rotifers, turkey and some lizards, the female gametes can form a new organism without being fertilized. Such a phenomenon is known as parthenogenesis.E.g. honeybees, some lizards etc. Post-fertilization It is the last of the sexual reproduction steps after zygote formation. Zygote is the vital link between two successive generations. The main highlights of this said stage are – embryogenesis and cell division. In simple words, embryogenesis is the process in which a zygote develops into an embryo. It is during embryogenesis that the zygote goes through both cell division and cell differentiation. Additionally, they are responsible for the modification and formation of tissues and organs and facilitate the formation of an organism. Based on the site of zygote’s development, animals are - viviparous and oviparous. An oviparous animal is an animal that produces eggs that later hatch to produce the young ones after being propelled out of the body of the female. ● Oviparity is the property of these animals where the fertilization may be external or internal, but the young ones are always hatched out of the body.● Oviparous animals include most fishes, amphibians, reptiles, and even birds. Some invertebrates like insects are also oviparous.● Ovoviviparous is another group where the eggs hatch inside the body of the animals, and the young ones come out. This is common in some snakes, sharks, and other animals.● Oviparity has been an evolutionary strategy in many animals where some produce many small and fragile eggs while others produce few but strong and large eggs. Thus, the production of many eggs increases their chances of survival and thus works as a strategy for reproductive fitness.Some animals like frogs might undergo external fertilization where the female first lays the eggs, and the male comes to spread its sperm to fertilize the egg. The fertilized egg then develops until a tadpole hatches out of it.However, in other animals like hen, the male inseminates the female, resulting in internal fertilization. The female then lays and looks after the fertilized egg hatches into a chick. ● The eggs of oviparous animals are covered with hard or soft shells, depending on the animals. The size of the eggs is also characteristic of the animal.● After laying the eggs, some animals sit on the eggs to keep them warm while others bury the eggs in the sand.● In reptiles, the temperature of the egg is critical during embryonic development as it determines the sex of the offspring.● Oviparous animals usually produce eggs at a particular time of the year depending on the availability of food as they provide nutrients to the egg through the yolk sac.● Chickens lay eggs that might or might not be fertilized. In the case of the unfertilized egg, the egg doesn’t hatch to produce a young one but instead is taken by humans as a source of the nutrient.● Examples of oviparous animals include frogs, snakes, lizards, hens, duck, fishes, shark, penguins, butterflies, octopus, etc. A viviparous animal is an animal that develops an embryo inside the body of the female, resulting in the live birth of a young one.● The embryo develops in special organs within the body of the female where the mother provides necessary nutrients to the embryo.● Viviparous animals are present in all groups of vertebrates except birds. Fish, amphibians, reptiles, and mammals all have members that are viviparous even though none of the groups is exclusively viviparous.● It has been assumed that viviparity developed from oviparity where the egg stayed inside the female for longer, causing it to hatch into a young one. Nutrition in different viviparous animals differs as some primitive animals have a yolk sac that provides nutrients to the embryo. In contrast, in others, the embryo develops into larvae inside the mother feeding on secretions from the reproductive parts of the mother. ● In mammals, however, the mother provides nutrients to the new-born via the secretions of the mammary glands.● Viviparous animals reproduce sexually via internal fertilization as the embryo develops inside the body of the mother.● Viviparous animals are also advanced in that they can carry the developing young ones with the mother from areas with many predators.● Similarly, viviparous animals can also reproduce any time of the year as they can feed the embryo with the fat reserves in the body.● However, viviparity might be very tiring for the mother as it might cause severe damage to the reproductive parts during birth.● Parental care after birth differs in different viviparous animals where some mammals like humans look after the young ones while some salamanders show no parental care at all. Examples of viviparous animals include humans, bears, giraffes, cattle, some sharks, salamanders, some frogs, etc. Also, in flowering plants, the ovary starts developing after fertilization. Subsequently, the ovules mature, which contain the embryo.