Class 12||Chapter 2|| Sexual Reproduction in flowering plants

This chapter includes flowers, their detailed structure and developmental processess which took place durin sexual reproduction. Helpful for Board and NEET students.

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1. Chapter 2 Sexual reproduction in flowering plants M.Sc. Zoology 9931787676

2. flower A  flower , sometimes known as a   bloom  or  blossom , is the reproductive structure found in flowering plants. The flower may be defined as a condensed shoot which has become specialized as reproductive organ. It is a condensed modified shoot or branch in which the leaves are extremely altered to form its parts. Flowers develop from a stem branch either in a terminal or axillary position.

3. Parts of a typical flower Flowers present a great diversity in their structure. A typical flower consists of four distinct whorls of floral leaves and These may be divided in to two main g roups. Non essential Parts or Outer whorl Calyx and Corolla Protection during reproduction Essential Parts or Inner whorl androecium and gynoecium They take part in reproduction

4. Sepals :- The outermost green leaf like parts that cover the unopened flower or bud are sepals . Taken collectively they form the calyx . Petals :- The inner leaf like structures are brightly coloured. Taken collectively they are called corolla. NOTE:- The sepals and petals, when not differentiated into calyx and corolla, are called perianth . Stamen :- It is the third inner part that produces pollen in which sperm or male cell originate. Collectively the stamens from androecium. Each stamen consist of a slender stalk or filament, supporting a knob like sac called the anther. It produces yellow or reddish powdery grains called pollen grains which play an important part in reproduction . Pistil :- It is the innermost organ that produces ovules within which female gamete originate. It has following parts:- Stigma :- Sticky structure for receiving the pollen . Style :- slender tube that supports stigma . Ovary :- The basal bulged part of the pistil is ovary. Inside ovary lies the ovarian cavity (locule). The placenta is located inside the locule. Ovule :- From the placenta megasporangia arises, commonly called ovules.

5. Male reproductive organ Stamen :- Stamens are composed of anther and filament. The anther lobe may be of two type: Monothecus (one lobe) Ex- China rose, cotton. Dithecus (two lobe) Ex- Datura. On the basis of attachment of anther lobe with filament stamens are of four types : Basifixed Adnate Dorsifixed Versatil e

6. Transverse section of anther(young)

7. This structure helps in microsporogenesis (a process of development of male gamete). Between both the lobes there is a layer of connective sterile tissue which does not participate in reproductive process. The area between microsporangia and outer anther layer is called anther wall which is made up of four layers: Epidermis - Outermost layer which helps in protection. Endothecium - This layer has radially arranged cells and these cells have callose thickening. Middle layer - Three to four layers of loosely arranged thin walled parenchyma cells. These three layers helps in dehisence.When anther matures, these three layer become rigid except the point of dehisence from where the anther ruptures. 4) Tapetum - It is innermost layer, cells are pyramid shaped and multinucleated with thick cytoplasm. Tapetum is a nutritive layer which provide nourishmment to the developing microspore. Tapetum also secrete callase which dissolve callose of microspore tetrad. Tapetum produces Ubisch bodies which are coated with sporopollenin which makes exine of the pollen grain. Sporopollenin is the most resistable substance found in the living world . Tapetum helps in formation of pollenkit and normally found as powdery substance. Ex- Hibiscus.

8. microsporogenesis The process of formation of microspores (male gamete) in microsporangium is called microsporogenesis . As the anther is young all these four microsporangia are filled with sporogenous cells called archesporial cells but as anther grows : 1)Its size also increases. 2)The size of microsporangium increases 3)The space between the cells increases and microsporangium now called pollen sac . Sporogenous cells are capable of forming microspores. Not all the sporogenous cells converts in to microspores rather few degenerates which is utilized by these sporogenous cells and it is now called microspore mother cell (MMC)/(PMC) which will undergo meiosis to form microspore. The pollen grains of a tetrad grow and separate from one another. Usually the arrangement of microspores in a tetrad is tetrahedral or Isobilateral . However, decussate , linear and T shaped are also found.

9. Tetrahedral Isobilateral Decussate T Shaped Linear Arrangements of microspore tetrad.

10. Pollen Grain The pollen grains represents the male gametophyte. Now, this pollen grain undergoes one mitotic division in which karyokinesis takes place first which is followed by cytokinesis. So, now nucleus will divide first and two nuclei would form and this is followed by cytokinesis which is not equal to both the nuclei. The separation of cytoplasm (cytokinesis) is not equal. One part of cell would get more cytoplasm while other will get less cytoplasm. The larger part will be called as vegetative cell or tube cell while the smaller cell is call generative cell. In most of the angiosperms , the pollen grain released at two celled (tube cell + generative cell) stage. Anther wall get fibrous and from point of dehiscence the anther get rupture and pollen grains are released. Allergy to pollen grains is called Hay fever .

11. Structure of Pollen grain

12. The hard outer layer is called exine which is made up of sporopollenin . It can withstand high temperature, strong acids and alkali. The inner wall of pollen grain is called intine which is made up of cellulose and pectin . When pollen grain matures it contains two cells vegetative cell and generative cell . The vegetative cell is bigger, has abundant food reserve and large irregular shaped nucleus. The generative cell is small and floats in the cytoplasm. Pollen grains are normally shed at 2 celled stage but in some species they may shed at 3 celled stage (generative cell divides mitotically to give rise to the two male gametes). Pollen grains are rich in nutrients. Pollen grains have to land on the stigma before they lose viability if they have to bring about fertilization. Pollen grains are stored at liquid nitrogen (-196 degree Celsius) which can be used as pollen banks.

13. The Pistil, Megasporangium (Ovule) and Embryosac The pistil is centrally situated female reproductive organ of the flower. The free unit of gynoecium is called pistil. The pistil may be made of single or many ovules. It may be simple or compound. A simple pistil is always is always monocarpellary . Such a pistil is found in the flowers of pea, bean, Gold mohur etc. In monocarpellary or simple pistil the ovary is single chambered. The compound or polycarpellary pistil may be of two types: a) Apocarpous :- In this condition, there are many carpel's but they are all free and each carpel forms a separate ovary. Ex- Rose, Lotus, Strawberry. b) Syncarpous :- In this condition, there may be two or more carpel's but they are always more or less fused with one another to form a single ovary. Ex- Mustard, Lady’s finger. In Angiosperms the ovule found is Anatropous and Bitegmic

14. Anatropous &Bitegmic ovule Funicle : It helps in the attachment of ovule with placenta. Ovule is attached to ovary with placenta. Hilum : The body of the ovule fuses with Funicle and the point of attachment is called Hilum. Nucellus : It provide nourishment to the developing embryo. Sometime the nucellus is less = Tanuinucellate and if nucellus is plenty = Crassinucellate . Micropyle end : The integument leaves a narrow passage known as Micropyle at one end of ovule. Pollen tube enters to the embryosac through Micropyle aperture. Chalazal end : The place of origin of the integuments usually lies at opposite end of Micropyle, known as chalaza . Integuments : Protects the inner tissues of ovule. Embryosac : Contains embryo which develop in to seed. Cells of nucellus towards Micropyle end get change into MMC (2n) and undergoes meiosis to give rise to megaspore.

15. megasporogenesis The process of formation of haploid megaspores from the diploid megaspore mother cell is called megasporogenesis. Generally, a single megaspore mother cell (MMC) differentiate in the micropylar region of nucellus. The MMC undergoes meiotic division which results in the production four haploid megaspore. In majority of angiosperms, only one of the megaspores is functional while the other three degenerates. During Megasporogenesis, one nucellar cell at Micropyle end form archesporial cell. This archesporial cell divides to form a primary parietal cell ( stops further division) and primary sporogenous cell which leads to the formation of MMC (2n) which undergoes 2 successive meiotic division to form 4 haploid megaspore which are arranged in linear tetrad.

16. Out of these four megaspore, three megaspore towards Micropyle degenerate and one towards chalaza enlarges to form functional megaspore. The functional gametophyte forms female gametophyte or Embryosac. Nucleus of megaspore divides mitotically (only karyokinesis, 3 times) to form 8 daughter nuclei and all haploid . Three nuclei migrate to the Micropyle end and get surrounded by cytoplasm to form egg apparatus (middle cell forms the egg and other two forms synergids or helping cell). The other 3 nuclei migrate towards chalazal end and get surrounded by cytoplasm and form 3 antipodal cells. 2 nuclei migrate to the middle and form 2 polar nuclei (both are haploid or may fuse to form a secondary nucleus (2n) with a central cell). Thus, 8 nucleated, 7 celled embryosac is formed. This is Monosporic (as it develops from one megaspore), 7 celled (3 antipodals+1 egg) and 8 nucleated embryosac is called polygonum type of embryosac .

17. Development of female gametophyte

18. Types of ovule There are following distinct types of ovules: A) orthotropous ovule : It is a straight or erect ovule. In this type the micropyle lies at one pole while the chalaza and Hilum lies at opposite pole. Thus, the micropyle, chalza and Hilum lies at same vertical plane. Ex- betel, long pepper, etc.

19. B) Circinotropous ovule : This upright position of ovule is achieved by complete rotation of the body. C) Anatropous ovule : This is an inverted type of ovule so that the integuments on one side is partly fused with the Funicle, forming a region known as Raphe . This type of ovule is more common and found in Pea, Gram, Castor etc. D) Hemianatropous ovule : It is transverse type of ovule where chalazal and micropyle are at perpendicular to Funicle. E) Amphitropous ovule : This is intermediate between orthotropous and anatropous ovule. The ovule is bent half way so that the long axis of the ovule comes to lie at right angel to the funiculus. Ex- Poppy. F) Campylotropous ovule : The body of the ovule get curved or bent round like a horse shoe shape so that the micropyle Funicle and chalaza come to lie at one pole but there is no fusion of the Funicle with the integument. Ex- Mustard.

20. The transfer of pollen grains from the anther to the stigma is termed as pollination . It may be of two types: A) Self pollination B) cross pollination In case of self pollination the pollen grains are transferred from the anther to the stigma or stigmas of the same flower. It is also termed as autogamy. In case of cross pollination the pollen grains are carried in various ways to the stigma or stigmas of another flower either on the same plant or on the different plant of same species. It is also known as allogamy/ Xenogamy.

21. Adaptations for self pollination Homogamy : Maturation of anther and stigma simultaneously. To ensure that self pollination takes place, the anther and stigma of the bisexual flower or those of the unisexual flower must mature at the same time. Ex- Mirabilis . CLEISTOGAMY : This is a condition in which flower remains closed . There are some bisexual flower which never open. As a result, the pollen grain are distributed on the stigma of the same flower. Such flowers are small, inconspicuous and lacks colours and fragrance . Ex- Oxalis, Viola, Commelina . These plants produce two types of flowers : Cleistogamous flower : (closed) adaptation for self pollination. Chasmogamous flower : (open) adaptation for cross pollination. HOMOGAMY CLEISTOGAMOUS CHASMOGAMOUS

22. GEOCARPY : As soon as fertilization takes place in ground nut plant , the stalk of the ovary elongates and starts growing towards the surface of the ground. Pedicle burries its tip containing ovary in ground and ovary give rise to underground fruit. In vinca rosea, anther are present at the mouth of tubular corolla and at maturity the stigma passes through the mouth of corolla tube resulting in self pollination. Arachis hypogea

23. Vinca rosea

24. In Mirabilis Jalapa (4o’clock plant), stamen bend on stigma on maturation of anther . In Solanum tuberosum , curving/coiling of style on anther. In sunflower, self pollination occurs if cross pollination fails .

25. Adaptation for cross pollination In majority of cases self pollination is prevented in a number of different ways which are as follow : Unisexuality / Dicliny : Dioecious flowers : In this case the flower are always unisexual but male and female flowers are borne on two different plants. Ex- Betel, Pepper vine, Mulberry. Unisexual flowers : In these also there are male and female flowers, but they are both borne on same plant. Thus in unisexual flower self pollination cannot take place. Ex- castor, cucumber, pumpkin. Bisexuality/Dichogamy : Maturation of stamen and pistil takes place at different time. This condition is known as Dichogamy due to which self pollination is prevented. Protandrous : Those flowers in which stamens mature earlier than the pistil. Ex- Jasmine, Coriander, Sunflower. Protogynous : Those flowers in which pistil mature and stigma become receptive earlier than the stamen in the same flower. Ex- Tobacco, Rose, Grasses.

26. Heterostyly Heterostylic flowers like primroses show very distinct adaptation to prevent self pollination. In this case stigma and stamen occur at two distinct positions and the pollen grain produced are adapted to stick to the stigma of the another flower. The length of stamen and style are different in different flowers. oxalis Evening prime rose Pin flower Thrum flower

27. Pre -potency - Pollen grains of another flower germinates rapidly than the pollen grains of the same flower over the stigma. Ex- apple, grape. self -incompatibility : This is a genetic mechanism that prevents self pollen (from the same flower or other flowers of the same plant) from fertilizing the ovules by inhibiting pollen germination or pollen tube growth in the pistil. Ex- Tobacco, Potato. Hercogamy : In certain flowers, stamens and pistil come to maturity at the same time, but still self pollination is avoided by means of following adaptation which form a kind of physical barrier to self pollination : The stamen and pistil may lie at some distance from each other. In Aristolochia the flowers are trumpet shaped and hang somewhat downwards and corolla act as a barrier. In many orchids and calotropis the pollen grains are held together by a delicate membrane which act as a physical barrier and the entire mass is known as pollinium , is formed at a place from where it can not reach the stigma by itself. The pollinia remain fixed in their position by adhesive disc and can only be carried away by insects. The anther may be inserted with in the corolla tube and the style is exerted or the vice versa and thus self pollination is avoided.

28. aristolochia calotropis

29. Advantages of cross pollination Cross pollination is more common in plants than self pollination because of following advantages:- It leads to the production of stronger and healthier seeds than self pollination. It provides mixing/blending of characters of two parents. so, it provides an opportunity for the production of the individuals with new and useful characters which is most likely to survive and produce well develop plants. It has been utilised by men to improve his crops and offer greater variety. Many different kinds of fruits and vegetables are primarily due to cross pollination. Ex- A strong, healthy, disease resistant crop is desired, and one which will produce good wheat grains for milling and making bread. Many other characters have been modified as a result of cross pollination.

30. Viability of pollen grains It is a period for which pollen (male gamete) possess the ability to fertilize the egg . Ex- Wheat, rice= 30 min. Most plant= few months Longest pollen= Zostera Larger pollen= Mirabilis Jalapa Smallest pollen= Myosotis . myosotis Smallest pollen Larger pollen

31. Anemophily (Wind pollination) It is a mode of cross pollination or transfer of pollen grains from a mature anther to the stigma of a pistil which is accomplished through the agency of wind. Pollen grains are produced very very large in numbers. Pollens are light weight, dry dusty so that they can be easily blown away by wind. In case of Pinus, the pollen grains may be winged which are found hundreds of kilometers away from the parent plants. The anther should be well exposed or we can say the flower should be well exposed above the leaf. In anemophilous flowers, anthers are versatile. Non-essential parts are either absent or reduced. Stigma is exposed, sticky, feathery or hairy. Flowers are not bright coloured and without nectar and fragrance. Anemophily is highly wasteful as it is non-directional. Ex- Maize, Wheat, Rice, Grass.

32. Hydrophily(water pollination) It is the mode of cross pollination or transfer of pollen grains from the mature anther of a flower to the stigma of another flower which is accomplished through the agency of water. In many aquatic plants with emergent flowers, pollination occurs by wind or insects, e.g., Lotus, Water Lily, Water Hyacinth. Flowers are small and inconspicuous. Floral parts are unwettable. Nectar and odour are absent. Pollen grains are light and unwettable due to presence of mucilage cover. Stigma is long, sticky but unwettable. Hydrophily is of two types— Hypohydrophily and Epihydrophily

33. Hypohydrophily Epihydrophily Pollination takes place under the water. Plants are submerged rooted. Zostera has the longest pollen grain needle like without exine. These pollen grains have same specific gravity as water so they remain in the water body. The stigmas are also long. The needle like pollen grains have great chances to touch the long stigmas and coil around the it to perform pollination. Ex- Zostera (Marine Angiosperms) or Sea grass. Plant is Dioecious and submerged rooted. The male flowers are arranged in a cluster called spadix while female flowers are produced on a long pedicel which grows until the flower reaches to the surface of water. After maturation, the male flower detaches from the cluster and moves up to the surface of water and the stamens are exposed. At the same time female flower are uncoils and reaches up to the surface of water. The pollens are released on the surface of water and pollination takes place and as soon as it happens the female flower again recoils. Ex- Vallisneria.

34. Zostera (Hypohydrophily)

35. Entompphily (by insects) The flowers are brightly coloured but if flowers are not coloured then some other parts must be coloured. Like in Bougenvellia , the bract is coloured, in Euphorbia , the leaf is coloured, in Mussaenda , the sepal is coloured. Scent/ fragrance is present. Like Jasmine. Flowers are conspicuous, if small then in clusters. May produce edible pollen grains. Like pappaver, Rosa. Nectar glands are present at such positions that the insect encounters anther and stigma. Flower shape and color may match an insect. The male moth sits on a flower conceiving it as a female moth to copulate it, but inturn pollinates the flower. Like Orchid flower. In Yucca flower - Yucca moth (Pronuba Yuccasella) drills a hole in the ovary of flower to lay her egg. The moth seals the hole with pollen grains from different yucca flowers. Now this plant and moth has a mutual relationship, means they can not survive without each other. Moth will get a safe place to lay her eggs and their larvae can feed on material inside so that their survival is confirmed and in turn flower will get pollinated as pollen grains are just near to the ovule.

36. Yucca Flower Bougenvillia Euphorbia Mussaenda

37. Post pollination changes Fertilization was discovered by STRASBURGER. Pollen-Pistil Interaction/ Identification : Pollen grains of various plants may land over stigma. The pistil recognise the pollen grains, whether it is of the right type (compatible) or of the wrong type (incompatible). Pistil accepts the right pollen and promotes its growth leading to fertilization where as the wrong pollens are rejected from germination. The events from pollen deposition on stigma, pollen germination and entry of pollen tube into ovule for fertilization are referred as pollen-pistil interaction.

38. Secretion from stigma : Stigma secretes a liquid mainly consist of water and sugar. This liquid is absorbed by pollen grains through germ pore and at a result of the intine stretches but due to exine it cannot stretch, from germ pore pollen tube germinates. Normally, only one pollen tube emerges known as Monosiphonous and if there are many pollen tube emerges then known as Polysiphonous . Growth of Pollen Tube : In most of the Angiosperms, Pollen grains are released at two celled stage, one bigger vegetative cell and a smaller generative cell. After formation of pollen tube, the generative cell undergoes one mitotic division and results in formation of two male gametes. Now, the whole cytoplasmic content including vegetative cell and two male gamete will pass through the pollen tube.

39. The style from which pollen tube is going to pass may be hollow or solid . In case of solid style, it may chance that pollen tube get little squeezed and may result in back flow of cytoplasmic content. To avoid this situation callose plugs are formed so that even if it get squeezed no content will go back.

40. There are three possibilities that pollen tube enters in the embryosac – A) If pollen tube enters through micropylar end and reaches to embryosac- Porogamy . B) If pollen tube enters through chalazal end end and reaches to embryosac- Chalazogamy . C) If pollen tube enters through integuments and reaches to embryosac- Mesogamy . Porogamy is most common among Angiosperms.

41. Entry of pollen tube in to embryosac : One of these two synergids starts to degenerates and the filliform apparatus of degenerating synergid guides the pollen tube to enter in to embryosac. As soon as the pollen tube enters in degenerating synergid, it ruptures and two male gametes are released and wall of degenerating synergid also dissolves.

42. Fertilization : 1 st male gamete (n)+Egg (n)= Zygote (2n) (Embryo) Triple Fusion : 2 nd male gamete+2 polar nuclei=Primary Endosperm Nucleus (PEN) [3n]. The developing embryo will get nutrition from endosperm. Fertilization and Triple fusion together known as Double fertilization . Double fertilization was explained by Nawaschin. Fertilization takes place first, hen triple fusion takes place i.e. if embryo is formed then only nourishment is required. If fertilization fails then endosperm will not form. FERTILIZATION FORMATION OF ENDOSPERM NUCLEUS(3n) DEVELOPMENT OF EMBRYO FORMATION OF NUTRITIVE TISSUE

43. Post fertilization changes The process of fertilization results in formation of diploid zygote and triploid PEN respectively. The diploid zygote represents the first cell of sporophytic generation and it develops in an embryo. The triploid PEN forms the endosperm for the nourishment of the embryo. The ovule changes into seed, the integument changes into seed coat and ovary forms the fruit. Normally, till these changes takes place all these nucellus get used up, but sometimes after formation of seed some part of nucellus still remains i.e., persistent nucellar containing seed is called perispermic seed. Ex-Beet root,Black pepper.

44. Formation of endosperm In angiosperms, the endosperms develops in three different ways: Free nuclear type : This is the most common type of endosperm development. The endosperm nucleus give rise to a number of free nuclei. The coconut water from a tender coconut id free nuclear endosperm having thousands of free nuclei(only Karyokinesis). Cellular Type : Division of PEN is immediately followed by wall formation so that endosperm is cellular. Ex- white part of coconut. Helobial Type : It is intermediate between nuclear and cellular and is common in monocots. The first division of PEN is followed by wall formation and after that free nuclear division continues. Ex- Asphodelus.

45. Formation of embryo DEVELOPMENT OF DICOT EMBRYO The zygote divides by a transverse division producing a Basal cell towards micropyle and a Terminal cell towards chalaza. Basal cell undergoes many transverse division to form a long suspensor (6-10 celled). The function of suspensor is to push the proembryo deep in to the endosperm. The terminal cell divides in various planes to form proembryo. The cell of suspensor towards proembryo functions as hypophysis , which divide to form 8 cells. 4 cells towards proembryo form root cortex and other 4 cells towards suspensor give rise to root cap and root tip . The terminal cell of suspensor towards micropyle swells and forms haustoria. The proembryo forms an octant (8 celled stage), of this octant 4 lower cells towards the suspensor forms hypocotyl and 4 cells towards chalaza give rise to plumule (shoot tip) and cotyledons. In beginning the embryo is globular , as it grows it become heart shaped and then get curved into a horse shoe shaped .

46. A typical dicotyledonous embryo consist of an embryonal axis and two cotyledons . The portion of the embryonal axis above the level of cotyledons is the epicotyl , which terminates with plumule or stem tip . The cylindrical portion below the level of cotyledons is hypocotyl that terminates at it lower end in the radicle or root tip . The root tip is covered with root cap. The seed is the final product of sexual reproduction in angiosperms . 1)Radicle develops from hypophysis. 2)Hypocotyl develops from the lower half of proembryo. 3)The two cotyledons and plumule develops from upper half proembryo.

47. .

48. Development of Monocot Embryo The zygote greatly enlarges in size and divide by two transverse division to form 3 celled proembryo. These 3 cells are- Basal cell (towards Micropyle end), Middle cell , Terminal cell (towards chalazal end). The large basal cell does not divide and is transformed in to a large basal cell. Terminal cell undergoes number of divisions in various plains and form a single cotyledon (Scutellum) . The middle cell undergoes transverse and vertical division and give rise to suspensor cells , Coleorrhiza (Radicle covered with scaly structures), Coleoptile (Plumule covered with scaly structures) and hypocotyl . In Monocots like Colocasia no suspensor is formed .

49. The cotyledon here is very thin & Papery and almost negligible reserve food material, but still we are saying it cotyledon. Why? Normally, Cotyledons have reserve food material but here the reserve food material has to pass on the developing embryo. Whenever the endosperm is digested, the digested endosperm first comes to cotyledon then through cotyledonary node it is passed on to the developing embryo.

50. Development of Seed Zygote develops into embryo. Triploid PEN give rise to nutritive endosperm which provides nourishment to embryo. Nucellus is used up during development of embryo. Integuments of Ovule dries up. The outer integument become hard and form Testa , while the inner forms membranous Tegmen . Micropyle remains in form of a small pore on the surface of seed. Oxygen and water enters the seed through this pore at the time of germination. Hilum marks the point of attachment of ovule to Funicle/Stalk. Dormancy of seed - Dormancy, is that phase in the lifecycle of a seed , when it fails to germinate even though the environmental condition which are normally considered favourable at present. Seed Viability - It is the capacity of germination under suitable conditions. It varies in different kinds of seed. In few species, seeds loose their viability with in a few month but large number of plants have several years of seed viability. Ex- Lupinus arcticus – Its seeds are excavated from Arctic tundra. They remain in dormancy for 10,000 years. Phoenix dactylifera (date palm) recently 2000 years old viable seeds excavated near dead sea.

51. Albuminous Seed/Endospermic Seed : If after formation of embryo, endosperm still remains as food storage tissue. Ex- Wheat, Barley, Maize, coconut etc. Ex-Albuminous/Non-Endospermic Seed : Endosperm is completely used up by growing embryo. For further development of embryo during germination, nutrition is stored in cotyledons. Ex-Gram, Pea, Bean etc. Occasionally, in some seeds such as black pepper, remains of nucellus also persistent. This residual persistent nucellus is the perisperm and such seeds are called perispermic seed .

52. Classification of fruits Fertilized ovary changes in to fruits and their study is called Pomology . They can be classified as follow: SIMPLE FRUITS : Single ovary of single flower. ( Unicarpellary, Multicarpellery Syncarpous ) AGGREGATE FRUITS : Multiple pistil of single flower. ( Multicarpellery Apocarpous ) COMPOSITE FRUITS : Fruits develops from complete inflorescence. Fruits can also be classified as: TRUE FRUIT / EUCARPS : Simple fruit. Ex-Mango, Pea. FALSE FRUIT / PSEUDOCARPS : Aggregate and Composite fruits. Ex- Apple, Pear, Brinjal etc.

53. The process of formation of embryo without the fusion of gametes is known as Parthenogenesis. Fruits are formed without fertilization is called Parthenocarpic fruits. Such fruits are either seed less or contain non-viable seeds. Parthenocarpy can be induced by the application of low concentration of Auxins and Gibberellins. The best varieties of Banana, Pineapple, grapes etc are Parthenocarpic. Parthenocarpic fruits have higher proportion of edible parts than normal fruits. Ethylene is a ripening hormone while Abssicic Acid (ABA) is a dormant hormone.

54. Apomixis A few flowering plants have evolved a mechanism to produce seeds without fertilisation called Apomixis . Apomixis is a form of asexual reproduction that mimics sexual reproduction. The term Apomixis was first coined by Winkler in 1908. Plant which shows Apomixis are known as Apomictic plants . There are several methods of apomictic development of seeds are as follow: Agamospermy : Formation of embryo from an unfertilized ovule i.e. Haploid gametes are not formed . Seeds and embryo are formed without meiosis and fertilisation. Adventive Polyembryony : Extra embryo develop from a diploid cell of nucellar tissue or integument. Ex-Citrus, Opuntia. Recurrent Agamospermy : A diploid embryosac is formed with diploid egg. All the cells of the embryosac are diploid as it is formed directly either from nucellar cell ( Apospory ) or diploid megaspore mother cell ( diplospory ). Non-Recurrent Agamospermy : Embryo develops from haploid female gamete without fertilisation.( Parthenogenesis ) Polyembryony: Development of more than one embryo in a seed. It was discovered by Leeuwenhoek in 1729 in Orange.

55. Artificial Hybridization It is useful to enhance quality of plants in plant breeding . Its purpose is to combine characters of two plants. Selection of plants. Selection of plants for male and female gametes. After selection the male reproductive part is removed and the process is called emasculation . Emasculation is only required when flower is bisexual. If flower is big than it is done manually and if flower is small than it is done by suction pump. Bagging is done to prevent any undesirable pollen grain to fall on stigma. So, female part is covered with a bag. Collection of a desired pollen grains through bagging. Dusting of desired pollen grains on stigma of emasculated flower. Fertilisation and seed formation. Testing of seeds by germinating in soil. If seed satisfies the new character then it is sold commercially.

56. THE END DOUBTS?? QUESTIONS??