Samacheer Class 12 Bio Botany - Asexual and Sexual Reproduction in Plants

Reproduction is the biological process of producing young ones of their own kind. It is a vital process for the existence of a species and it also brings suitable changes through variation in the offsprings for their survival on ear

Subaerial stem modifications.
The stem is partly aerial and partly underground.
a) Runner. (Ex. oxalis, Centella Asiatica)
* It is running horizontally on the soil surface.
* Nodes have axillary buds, scale leaves, and adventitious roots.
* Runner arises from the axillary bud.
* Mother plant produces many runners in all directions.
* They break off and grow into individual plants.
b) Sucker. (Ex. Musa (banana), chrysanthemum)
Grows horizontally for a distance under the soil. Then it emerges obliquely upwards.
c) Stolon (Ex. Strawberry, Vallisneria)
Develop from underground stems.
They grow horizontally outwards.
d) Offset (condensed runners)
Unlike runners, they produce tilt of leaves above and duster of roots below Ex. Pistia, Eichhornia.

• It is an artificial method of vegetative propagation.
• The stem of the parent plant is allowed to develop roots while still intact.
• The root develops. The rooted part is cut. It is planted to grow as a new plant.
• Ex. Ixora, Jasminum.

• Bryophyllum undergoes vegetative reproduction in the leaf.
• The succulent leaf is notched in its margin.
• Adventitious buds develop at these notches. They are called epiphyllous buds.
• These buds develop a root system. When the leaf decays, they become independent plants.

Grafting:
* In grafting, two different plants (stock & scion) are used to develop new plants.
* The new plant will support to possess the characters of both the parents or new variation can be noticed.
Layering:
* In layering, only one plant is used to develop a new plant.
* Variation cannot be expected. The new individual is exactly similar to the parent plant.

Micropropagation.
The growth of plant tissue in special culture medium under suitable controlled conditions is known as “tissue culture”.
it is the regeneration of a whole plant from a single cell or tissue.
Advantages.
* Rare, Endangered plants are propagated.
* In a short duration, plants with desirable characteristics can be multiplied.
* Produce Genetically identical plants.
* Done in any season.
* Plants without viable seeds (or) difficult to germinate can be propagated.
* Meristem culture produces disease-free plants.
* Cells can be genetically modified or transformed.

Mound Layering:
In mound layering, a lower flexible branch with leaves is bent to the ground and a part of the stem is buried in the soil and the tip of the branch is exposed above the soil. After the roots emerge from the buried stem, a cut is made in the parent plant so that the buried plant grows into a new plant.

Conventional methods of vegetative propagation.
a) Cutting (Ex. Hibiscus)
* Plant parts like stem, leaf are cut from the parent plant.
* Cut part is placed in suitable medium,
* It produces root and grows into a new plant.
b) Grafting (Ex. Citrus, Mango)
* Two different plants are joined.
* They grow as one plant.
* Plant in soil is called stock.
* Plant used for grafting is the scion.
* It is of 5 types.
i) Bud grafting – scion is placed in the incision of stock.
ii) Approach grafting – Cut surfaces of stock scion are tied together.
iii) Crown Grafting – Wedge-shaped scion is inserted into the cleft of stock.
iv) Tongue grafting – Stock and scion are cut obliquely scion is fit into stock and bound with tape.
v) Wedge grafting – Twig of the scion is inserted into slot in the stock.
c) Layering
Stem of parent plant is allowed to develop roots while still intact. The root develops. The rooted part is cut and planted to grow as a new plant.
I) Mound Layering
* Flexible branch is buried in soil.
* Roots emerge from buried stem. It grows into a new plant.
ii) Air Layering
* Nodal region is girdled.
* Hormones are applied.
* Rooting is promoted.
* This area is covered by moist soil.
* Roots emerge in 2-4 months.
* Roots branches are removed from parent. They are grown separately.

• 1682 – Nehemiah Grew mentioned stamens as the male organ of a flower.
• 1694 – R.J. Camerarius described the structure of a flower, anther, pollen, and ovule
• 1761 – J.G. Kolreuter gave a detailed account of the importance of insects in pollination.
• 1824 – G.B. Amici discovered the pollen tube.
• 1848 – Hofmeister described the structure of pollen tetrad.
• 1870 – Hanstein described the development of embryos in Capsella and Alisma.
• 1878 – E. Strasburger reported polyembryony.
• 1884 – E. Strasburger discovered the process of Syngamy.
• 1899 – S.G. Nawaschin and L. Guignard independently discovered Double fertilization.
• 1904- E. Hanning initiated embryo culture.
• 1950 – D.A. Johansen proposed classification for embryo development.
• 1964 – S. Guha and S.C. Maheswari raised haploids from Datura pollen grains
• 1991 – E.S. Coen and E.M. Meyerowitz proposed the ABC model to describe the genetics of initiation and development of floral parts
• 2015 – K.V. Krishnamurthy summarized the molecular aspects of pre and post-fertilization reproductive development in flowering plants.

The genetic ability of a plant cell to produce the entire plant under suitable condition is said to be totipotency.
* This characteristic feature of a cell is utilized in horticulture, forestry and industries to propagate plants.
* The mature phloem parenchyma cells removed from the carrot were placed in a suitable medium under controlled conditions.
* It stimulate to start dividing again to produce a new carrot plant.
Importance of modern methods of reproduction in plants.
* Rapid Multiplication of desired plants in short duration.
* Genetically identical plants are produced.
* Tissue culture can be done at any season
* Plants without viable seeds (or) difficult to germinate can be propagated.
* Rare, Endangered plants are propagated.
* Meristem culture produces disease-free plants.
* Cells are genetically modified or transformed.

• It is the cross-pollination of flowers by beetles. They feed on pollen or juicy tissues of their flower.
• The plants using this mode of pollination
• Er. Nymphaea species of plants – Rhinoceros beetle.
• Giant Water lily – Scarab beetle
• Illicium plant – Diptera files.

1) Dichogamy
Anthers and stigmas mature at different times.
* Protandry – Stamens mature earlier.
* Protogyny – Stigmas mature earlier.
2) Herkogamy
* Self pollination is impossible by the arrangement of stamens and stigmas.
* Ex: In Hibiscus, stigmas project above the stamens.
* In some plants, when the pollen grain of a flower reaches the stigma of the same.
* It is unable to germinate or prevented to germinate on its own stigma.
* It is a genetic mechanism.
Example: Abutilon, passiflora.

Endosperm of Angiosperms
* Triploid Endosperm
* Endosperm is formed by triple fusion.
* Endosperm surrounds the embryo.
Endosperm of Gymnosperm
* Haploid endosperm.
* The endosperm is formed before fertilisation.
* Gymnosperms (Ex; pine) produce embryos. It provides nutrition as starch. with many cotyledons. Primary Endosperm is used as food.

Polyembryony
* The occurrence of more than one embryo in a seed is called poly embroyony.
Practical Applications.
* Seedlings from nucellar tissue of citrus are better clones for orchards.
* Embryos from polyembryonic are virus-free.

The inner tangential wall develops bands (sometimes radial walls also) of cellulose (sometimes also slightly lignified). The cells are hygroscopic. The cells along the junction of the two sporangia of an anther lobe lack these thickenings. This region is called stomium. This region along with the hygroscopic nature of endothecium helps in the dehiscence of anther at maturity.

• Supplies nutrition to developing microspores.
• Contributes sporopollenin through ubisch bodies. They play role in pollen wall formation.
• Pollenkitt material is contributed by tapetal cells. It is layer transferred to pollen surface.
• Exine proteins for rejection reaction are derived from tapetal cells.

Pollenkitt is contributed by the tapetum and coloured yellow or orange and is chiefly made of carotenoids or flavonoids. It is an oily layer forming a thick viscous coating over pollen surface. It attracts insects and protects damage from UV radiation.

Tenuinucellate ovule
* The sporogenous cell is hypodermal
* It has single layer of nuclear tissue.
* It has very small nucellus
Crassinucellate ovule
* These ovules have sub-hypodermal sporogenous cell
* They have large nucellus.
* Many layers of cells are seen.

In gymnosperms, the ovules are exposed and the pollens are deposited directly on it. Hence the pollution is direct in a gymnosperm. Whereas in angiosperms it is said to be indirect, as the pollens are deposited on stigma or the pistil.

* Heterostyly is a mechanism to promote cross-pollination.
* Different forms of flowers with different lengths of stamen and style.
* Pollination takes place between organs of same length.
a) Distyly. (Ex. Primula)
* Thrum-eyed flowers have short styles. Anthers of pin have short stamen.
* Anthers of thrum-eyed flowers and stigma of the pin are of the same height (both are long). This helps in effective pollination.
b) Tristyly (Ex. Lythrum)
3 kinds of flowers are there, with respect to the length of style and stamens. Flower of one type can’t pollinate their own type. They pollinate the other 2 types.

The characteristic features of entomophilous flowers are as follows:
* Flowers are generally large or if small they are aggregated in dense inflorescence. Example: Asteraceae flowers.
* Flowers are brightly coloured. The adjacent parts of the flowers may also be brightly coloured to attract insects. For example in Poinsettia and Bougainvillea, the bracts become coloured.
* Flowers are scented and produce nectar.
* Flowers in which there is no secretion of nectar, the pollen is either consumed as food or used in building up of its hive by the honeybees. Pollen and nectar are floral rewards for visitors.
* Flowers pollinated by flies and beetles produce foul odour to attract pollinators.
* In some flowers, juicy cells are present which are pierced and the contents are sucked by the insects.

Formation of haploid microspores from diploid microspore mother cell by meiosis.
* The primary sporogeneous cells undergo mitosis to form sporogenous tissue. ‘
* Sporogenous tissue functions as microspore mother cells.
* Microspore mother cell divides meiotically to form a tetrad (4 haploid microspores)
* Microspores get separated. They remain free in the anther locule. They develop into pollen grains.
* Microspores are held together by pollinium. Filament (or thread) like part form pollinium is called retinaculum. Through retinaculum pollinia are attached to clip like corpusculum. This structure is called Translator (Y shapled).

• Ovule of ovule (Megasporangium)
• It has a stalk and a body.
• stalk (funiculus) is at the base of ovule. It attaches ovule to the placenta.
• Hilum is the junction (point of attachment) between ovule and funicle.
• In an inverted ovule, the funicle is fused to the body of ovule. Thus a ridge called raphe is formed.
• Body of ovule has central mass of reserve food called nucellus.
• Nucellus is covered by 2 layers, called integuments.
• Integument covers the nucellus completely except at the top. This forms a pore called micropyle.
• Ovule with single integument is called unitegmic.
• At the base of body, nucellus, integument and funicle meet. This is called chalaza.
• Sac like structure in nucellus towards micropylar end is called embryosac (or) female gametophyte. It is formed from functional megaspore of nucellus.
• The nutritive inner intergument layer is called integumentary tapetum or endothelium.
• Tenuinucellate type ovule has hypodermal sporogenous cell. It has single layer of nucellar tissue.
• Crassinucellate type, ovule has subhypodermal sporogenous cell.
• Group of cells between chalaza and embryosac is called hypostase.
• Thick walled cells above micropyle are called epistase.

Steps in the fertilization of Angiosperms
1. Germination of pollen to form pollen tube in the stigma.
* Pollens fall on receptive stigma.
* Compatible pollen germinates to form a tube.
* This is helped by stigmatic fluid in wet stigma and pellicle in dry stigma.
* Compatibility is decided by recognition, rejection protein reaction, between pollen and stigma surface.
* Pollen undergoes hydration. Pollen wall proteins cire released.
* The entire content moves into pollen tube.
* Growth is at the cytoplasmic contents at the tip.
* The remaining part of pollen tube is occupied by a vacuole.
* It is cut off from tip by callose plug.
* The hemispherical, transparent pollen tip of pollen tube is called ‘cap block.
* The “cape block” disappears and the growth of the pollen tube stops.
2. Growth of pollen tube in the style.
* Hollow style glandular canal cells secrete mucilaginous substance. These secretions are nutrition for growing pollen tube. They control compatibility of style and pollen tube.
* In solid style the pollen tube grows through the intercellular space of transmitting tissue. Semisolid style is intermediate between solid and open type.
3. Entry of the pollen tube into the ovule.
* Propgamy – Pollen tube enters through the micropyle.
* Chalazogamy – Pollen tube enters through chalaza.
* Monogamy – Pollen tube enters through integument.
4. Entry of pollen tube into the embryo sac.
* Pollen tube enters embryosac at the micropylar end. It is guided by an obturator.
* Pollen tube enters into one of the synergids.
5. Double fertilization and Triple fusion.
* In Angiosperms, both the male gametes are involved in fertilization, it is called double fertilisation.
* One of the male gametes fuses with the egg nucleus (syngamy). Thus zygote is formed.
* The second gamete migrates to central cell. It fuses with polar nuclei (or) secondary nucleus. Thus primary Endosperm nucleus is formed. This involves the fusion of 3 nuclei so it is called Triple fusion.

Structure of Dicot seed
* Two cotyledons
* Two seeds may be seen
* The seed coat has outer coat testa and inner tegmen.
* In pea the cotyledons store the food. In castor the endosperm, stores reserve food.
* Coleoptile (sheath of plumule) coleorhiza (sheath of radicle) are absent.
Structure of Monocot seed:
* Only one cotyledon
* Paddy is one-seeded.
* Seed is enclosed by husk. The brown membranous seed coat closely adheres to grair
* Scutellum supplies embryo with food from endosperm through epithelium
* Coleoptile and coleorhiza are seen.

In some plants, fruit-like structures may develop from the ovary without the act of fertilization. Such fruits are called parthenocarpic fruits. Invariably they will not have true seeds. Many commercial fruits are made seedless.
Examples: Banana, Grapes, and Papaya. Nitsch in 1963 classified the parthenocarpy into the following types:
* Genetic Parthenocarpy: Parthenocarpy arises due to hybridization or mutation.
Examples: Citrus, Cucurbita.
* Environmental Parthenocarpy: Environmental conditions like frost, fog, low temperature, high temperature etc., induce Parthenocarpy. For example, low temperature for 3-19 hours induces parthenocarpy in Pear. Chemically
* induced Parthenocarpy: Application of growth-promoting substances like Auxins and Gibberellins induces parthenocarpy.
* Significance: The seedless fruits have great significance in horticulture.
* Seedless fruits have great commercial importance.
* Seedless fruits are useful for the preparation of jams, jellies, sauces, fruit drinks, etc.
* A high proportion of edible parts is available in parthenocarpic fruits due to the absence of seeds.
12th Bio Botany Guide Asexual and Sexual Reproduction in Plants in Animals Additional Important Questions and Answers
I. Choose the correct answer

• It is a third type of tapetum.
• The cell wall is not lost.
• Cells protrude into the anther cavity, by amoeboid movement.
• It is connected to male sterility. It is not periplasmodial type.

Exine Intine:
* Outer wall layer of pollen
* Thick
* Not uniform. Made of cellulose, sporopollenin, pollenkitt.
Intine:
* Inner wall layer.
* Thin
* Uniform made of pectin, hemicellulosc, cellulose, callose.

Pollen is preserved in liquid nitrogen (-196°C) in viable condition for prolonged duration. It is called cryopreservation. This pollen of economically important plants are stored in pollen bank.

In the ovule, a single hvpodermal cell in the nucellus become enlarged. “I his functions as Archesporium. In some plants it functions as megaspore mother cell directlv. It mev divide.

Pollination in Gymnosperms
* Direct
* Pollens are directly deposited on the exposed ovules.
Pollination in Angiosperms:
* Indirect
* Pollens are deposited on the stigma of pistil.

• During the developement, the two cells of the basal cell undergoes several transverse division into form a six to ten called suspensor.
• The suspensor helps to push the embryo deep into the endosperm.

• The seeds of paddy is one seeded and is called Caryopsis.
• The embryo is small and consists of one shield shaped cotyledon known as scutellum.
• It is present towards lateral side of embryonal axis.

• The activation of micellar tissue or an\ other cells (sporopln lie ceils of the ovule) can produce more’ Ilian one embryo, known as poly embryonv.
• The seedlings formed from the nucellar tissues in citrus are found belter clones lor orchards.
• They are Disease resistant (virus free) and are preferred by Agriculturists than the normal seedlings.

Pineyed flower:
Pin or long stv!e, long stigma tic pa iliac, short stamens and small pollen grains.
Ex: primula
Thrum eyed flower:
Thrum-eved or short style, small stigmatic papillae, long stamens and large pollen gains.

Coleoptile Coleorhiza:
The plumule is surrounded bv a proteetive sheath called coleoptile.
Coleorhiza:
The radicle including root cap is also covered bv a protects e sheath called coleorhiza.
III. Three Marks

• It is common among dicots. It is character¬ized by the presence of central core of elorgated highly specialised cells called transmitting tissue.
• This is equivalent to the lining cells of hollow style and does the same function.
• Its contents are also similar to the content of those cells. The pollen tube grows through inter-cellular spaces of the transmitting tissue.

Endospermous seeds:
* Seeds with endosperm
* It is also called ex-albuminous seeds
* Ex-Pea, Ground nut, bean
Non-Endospermous seeds:
* Seeds without endosperm
* It is also called albuminous seeds
* Paddy, Coconut, Castor.

• These are layers of specialized cells around the endosperm, in cereals.
• They have sphaerosomes (Ex. Barley, Maize) During germination, they secrete hydrolytic enzymes amylase,
• protease. They digest reserve food of endosperm.

• Eventhough Grafting is considered as artifica! method of vegetative reproduction, it is realtv used to produce plants combining favourable stem characteristics with root characteristics.
• The stem of the plant to be grafted is known as scion and the root is called stock.
• Here, one fnbrid is produced unlike in other method where manv number of plants are produced.

• In Bee orchid (ophyrus) the morphology of flower is similar to female wasp (colpa).
• Male wasp mistakes the flower for female wasp, and try to copulate. This pseudocopulation helps in pollination.
• In pea cotyledons store food.

• Fertilisation forms fruits and seeds.
• Pollination brings male and female gametes closer.
• Cross pollination produces variations, due to mixing of genes. Variations help the adaptation of plants to environment. It helps in specifiation.

* Coconut milk is a nutrient medium.
* It induces the differentiation of embryo (embryoids), Plantlets of various plant tissues.
* Coconut water is free nuclear endosperm. The white kernel part is cellular.
IV. Five Marks

• Seeds are attached to fruits by funiculus.
• The scar of funiculus is called hilum.
• Micropyle is the small pore below hilum.
• O2 and water enters seed for germination through micropyle.
• Each seed has outer thick seed coat.seed coat develops from the integuments of ovule.
• Testa is the hard outer coat.
• Tegmen is the thin membranous inner coat.
• In pea testa, tegmen are fused.
• Two cotyledons are laterally attached to embryonic axis.
• In castor endosperm has reserve food.
• One end of embryonal axis projecting beyond the cotyledons. It is called radicle (embryonic root)
• The other end of embryonal axis called plumule (embryonic shoot)
• Embryonic axis above the cotyledons is epicotyl.
• Cylindrical region between the cotyledons is hypocotyl.
• Epicotyle terminates in plumule. Hypocotyl ends in radicle

• Paddy is a one seeded caryopsis.
• The seed is enclosed by brown husk with 2 rows of glumes.
• The brown, membranous seed coat is attached to grain.
• Endosperm is the bulk of grain. It is the storage tissue.
• It is separated from embryo by epithelium.
• Embryo has one cotyledon called scutellum. It is later to embryonal axis.
• A short axis with plumule and radicle is protected by root ‘ cap.
• Coleoptile is a protective sheath of plumule.
• Coleorhiza is the protective sheath of radicle.
• Scutellum supplies food to embryo from endosperm through epithelium.

it is tile plant reproduction which does not involuo the union of male and female gametes.
A) Recurrent Apomixis.
Vegetative Reproduction and agamospernw.
B) Non recurrent Apomixis.
Alter meiosis, haploid embrvosoe is lormed.
It devleps into emhrvo without fertilization.
I) Vegetative Reproduction
Eiopagation of plants by parts other than seeds.
Ex. bulbil – I’riiiliaria imperialis.
Bulbs – Allium
Sucker – Chrysanthemum.
a) Agamospory
Embryos are rormed without syngamy and meiosis.
b) Advcntiver Embryony
Embrvo arises from diploid sporopln tic coll of nuceilus or integument, lt is called sporophytic budding, Gametophylic phase is completeh absent.
c) Diplospory (Generative apospory)
Megaspore mother ceils gives rise to diploid embrvosac without meiosis. ex. Eupatorium.
d.) Apospory
Nucellar cell develop into diploid emhryo sac. This is somatic apospory. Ex. Hieracium, parthenium.

Heterostyly:
* Some plants produce two or three different forms of flowers that are different in their length of stamens and style
* Pollination will take place only between organs of the same length. Distyly: Eg Primula Herkogamy:
Herkogamy
* Stamens and stigmas are arranged in such a way preventing self pollination.
* Stigmas project for above the stamens Eg: Hibiscus

The genetic ability of a plant cell to produce entire plant in suitable condition is called Totipotency.
i) Tissue Culture
Growth of plant tissue in special cutture medium under suitable conditions is called tissue culture.
Ex. F.C steward of Cornell University developed a new carrot plant from the phloem parenchyma cell.
ii) Micropropagation
Regenerationof whole plant from a cell or tissue of vegetative structures.
* Advantages of Modern methods.
* Plants with desired characteristics are multiplied rapidly in short duration.
* Genetically identical plants are produced.
* Done at any season.
* Plants without viable seeds, difficult to germinate can be propagated.
* Rare, endangered plants are propagated.
* Meristem culture produces disease free plants.
* Cells are transformed by genetic modification.
Disadvantages of modem methods
* Labour intensive. It requires skilled workers.
* Maintenance of sterile condition increases cost.
* Genetically identical clones are susceptible to new diseases.
* Genetical changes in callus is not desirable for commercial use.

1. Anther Wall
a) Epidermis
* Protective single layer.
* Cells undergo anticlinal division to cope up enlarging internal tissue.
b) Endothecium
* Single layer of radially elongated cells.
* Bands of cellulose (or) lignin are seen in tangetial wall.
* At the junction of 2 sporangia these thickenings are absent. This region is called stomium.
* Hygroscopic nature of endothecium helps in dehiscence of anther.
c) Middle layer
* 2 to 3 layers next to endothecium.
* These are ephemeral. Disintegrate or crushed during maturity.
d) Tapetum
* It is dual in origin (from peripheral wall layer and connective tissue of anther lining.
* It nourishes sporogenous tissue, microspore mother cell, microspores.
* Cells are uninucleate, multinucleate with polyploid nucleus.
* It contributes to wall material, sporopollenin, pollen kitt, tryphine.
* It controls fertility or sterility of pollengrains. It is of 2 tvpes i) Secretory tapetum ii) Invasive tapetum
2. Anther cavity.
* It is filled with young microspores or mature pollengrains.
* Microspore mother cells form microspore by meiosis.
3) Connective.
* It is a colume of sterile tissue. It is surrounded by anther lobe. It has vascular tissue.

• Haploid microspore is the first cell.
• Development takes place at microsporangium.
• Microspore nucleus divides into vegetative and generative nucleus.
• Large vegetative cell and small generative cell is formed.
• At this 2 celled stage, pollens are liberated from anther.
• In some plants generative cell form 2 male gametes.
• Male gametophyte grows when the pollen reaches the right stigma.
• Pollen absorbs moisture and swells.
• Intine grows as pollen tube through germ pore.
• At the 2 celled stage, generative cells divides into 2 male cells at stigma.

1. Orthotropous
* Micropyle is at distal end,
* Funicle and chalaza lie in one straight vertical line (Ex. Piperaceae)
2. Anatropous
* Body of ovule is inverted.
* Micropyle, funiculus lie close to each other Ex. Dicots, Monocots.
3. Hemianatropous
* Body is transverse
* It is at right angle to funicle. Ex. Primulaceae.
4. Campylotropous
* Body is curved at micropylar end. Embroysac is curved.
* Hilum, micropyle and chalaza are nearer. Ex.Leguminosae
5. Amphitropous
Less distance between hilum and chalaza. Nucellus is horse shoe shaped. Ex. Alismataceae.
6. Circinotropous. (Ex. Cactaceae)
Long funicle surrounds the ovule.

• Functional megaspore is the first cell of embryosac or female gametophyte.
• Megaspore elongates along micropylar – chalaza! axis.
• Nucleus undergoes mitosis without wall formation.
• A central vacuole expands and pushed the nuclei towards the opposite poles.
• Each nucleus divide mitotically twice. Thus 4 nuclei are formed at each pole.
• Eight nuclei are in common cytoplasm.
• Of the 4 nuclei at micropylar end, 3 nuclei form 3 antipodal cells. Fourth one is the lower polar nucleus.
• Two polar nuclei fuse into secondary nucleus.
• Thus 7 celled, 8 nucleated embrovsac is formed.

1) Dicliny or Unisexuality. ’
In unisexual flowers, only cross pollination is possible,
i) Monoecious (Ex. coconut)
* Male and female flowers on same plant
* Autogany is prevent in castor, maize. Geitonogamy takes place.
Dioecious.
* Male and female flowers are on different plants.
* Both autogamy, geitonogamy are prevented.
2) Monocliny or Bisexuality.
i) Dichogamy.
Anther and stigma mature at different times.
* Protandry (Ex. Helianthus)
Stamens mature earlier than stigma
* Protogymy (Ex. Aristolochia)
Stigmas mature earlier than stamen.
ii) Herkogamy.
Arrangement of stamen, stigma are different. Thus self pollination is prevented.
Ex. Hibiscus – Stigma project above stamen.
iii) Heterostyly,
Flowers differ in the length of stamen and style.
Pollination takes place between organs of the same length.
a) Distyly.
Pin flowers have long style. Thrum eyed flowers have long stamens. This same height helps in pollination.
Pin flowers have short stamens. Thrum eyed flowers have short style.
This helps in pollination.
b) Tristyly (Ex. Lythrum)
Plant produces 3 kinds of flowers with respect to length of style and stamens.
iv) Self sterility / Self incompatibility. Pollengrain of one flower is unable to germinate in the stigma of the same.
Ex. Passiflora

• Flowers in pendulous, catkin like, spike inflorescence.
• Inflorescence axis elongates. So, flowers are brought above leaf level.
• Reduced perianth (or) Absent.
• Small, colourless flowers do not / secrete nectar. The are not scented
• Long, exerted, versatile filaments.
• Enormous quantitv of pollen grains.
• Minute, light, dry pollen easily cart ied by wind to long distances.
• Violent bursting of anthers release the pollengrains. Ex. Urlica.
• Protruding, feathery, branched stigma catch pollengrains.
• Flowers are produced before leaves. So, they are carried without hindrance.

• Maize is monoecious and unisexual.
• Male inflorescence is at the terminal.
• Female inflorescence is at the lateral lower level.
• Heavy pollens cannot be carried by breeze.
• Male inflorescence is shaken by wind. The released pollens fall vertically below
• Male inflorescence (Tassel) Female inflorescence (Cob)
• The long stigma (23 cm) projects beyond the leaves.
• Pollens dropping from tassel is caught by the stigma.

• Salvia is adapted for bee pollination.
• Bilabiate corolla has 2 stamens.
• Each anther has upper fertile lobe and lower sterile lobe separated by long connective. The anthers swing freely.
• The bee strikes against the sterile end of connective. So, fertile part of stamen descend. It strikes at the back of the bee.
• When the bee visits another flower, the pollen is rubbed on stigma. Thus pollination is

• The embryo develops at micropylar end of embryo sac.
• The zygote undergoes transverse division.
• An upper terminal cell and lower basal cell is formed.
• Divisions in zygote during development lead to the formation of embryo.
• Before mature stage, embryo undergoes globular, heart shaped stages.
• Mature embryo has a radicle, 2 cotyledons and a plumule.

Pollination occurs at water level Pollination in vallisneria.
* It is submerged rooted hydrophyte.
* At the time of pollination, the flowers come to water level by long coiled stalk.
* Cup shaped depression is formed in female flower.
* The detached male flower floats on water surface.
* Male flower gets settled on the depression of female flower. It contacts stigma and bring out pollination.
* Stalk of female flower coils. Thus the flower comes under water from surface. Then fruits are produced.

Advantages of conventional Methods.
* Plants are genetically uniform.
* Plants are produced quickly.
* For plants with little or no seeds (or) when seeds do not germinate.
* Economical vegetative propagation. Ex. Solanum tuberosum,
* Plants with desirable characters like disease resistance, high yield can be grafted.
Disadvantages.
* Virus infected plants produce virus infected new plants.
* Bulky vegetative structures are difficult to handle.

Biosporic megaspore:
* of the four megaspores if two are involved in Embryo Sac formation the development is called bisporic.
* Example: Allium
Tetrasporic megaspore
* If all the four megaspores are involved in Embryo Sac formation the. development is. called tetrasporic.
* Example: peperomia