Pollination Detailed Explanation with examples

Pollination and Its types with examples.Contrivances of self - Pollination and Cross - Pollination.Agents of Pollination is also clearly mentioned.The topic is clearly explained with relevant images for better understanding.

1. Prepared By: Sumita S inha (M.Sc-LS,B.Sc.B.Ed )

2. POLLINATION LEARNING OBJECTIVES: To know about pollination. To develop understanding about the types of pollination. To make students aware about the contrivances of self -pollination and cross-pollination. Identify the agents of pollination.

3. INDEX Introduction Types of pollination Self pollination Contrivances for Self-Pollination B. Cross pollination Contrivances for cross-Pollination 3. Agents of pollination

4. INTRODUCTION Pollen is a fine to coarse powdery substance comprising pollen grains which are male microgametophytes of seed plants, which produce male gametes. Pollination is the transfer of pollen grains from the anther of one flower to the stigma of the same or another flower.  later enabling   fertilization and the production of seeds.

5. TYPES OF POLLINATION

6. SELF-POLLINATION 1.Self Pollination- The transfer of pollen from the anther of a flower to the stigma of the same flower or sometimes to that of a genetically identical flower (as of the same plant or clone). (a) Autogamy : It is the kind of pollination in which the pollen from the anthers of a flower is transferred to the stigma of the same flower, e.g., wheat, rice, pea , etc. (b) Geitonogamy : It is a kind of pollination where the pollen grains from the anther of the flower are transferred to the stigma of another flower borne on the same plant but at different branches. It usually occurs in plants, which show monoecious condition, e.g., Cucurbita .

7. Contrivances for Self-Pollination: The major adaptations which favours self pollination are; Bisexuality- Flowers should be bisexual or hermaphrodite, e.g., Hibiscus etc. Homogamy- In this method, both the anthers and the stigma mature at the same time, e.g ., Mirabilis, Potato ,wheat ,Rice , etc . Cleistogamy - In some plants, flowers never open up and the anthers dehisce inside these closed flowers to ensure pollination. Thus, cleistogamous flowers are invariably autogamous as there is no chance of cross-pollination. These flowers produce assured seed sets even in the absence of pollinators, e.g., Oxalis, Viola, etc. Viola Homogamy

8. CROSS-POLLINATION 2.Xeno-gamy (Cross-Pollination): It involves the transfer of pollen grains from the flower of one plant to the stigma of the flower of another plant. This is the only type of pollination which brings genetically different types of pollen grains to the stigma during pollination, e.g., papaya, maize, etc.

9. Contrivances for Cross-Pollination : Nature favours cross- pollination. All uni­sexual flowers and a large majority of bisexual flowers are naturally cross-pollinated . ( i ) Diclincy or unisexuality : Cross-pollination is the rule among diclinous plants , i.e., those bearing unisexual flowers. In dioecious (male and female flower borne on different plants) plants nothing else can take place. In monoecious plants (male and female flower borne on same plant) the only alternative is geitonogamy which, however, has the same effect as self-pollination . (ii) Self-sterility or Incompatibility : When pollen grain of an anther do not germinate on the stigma of the same flower or a flower of the same strain of plants. In some orchids, flowers wither away if pollinated by its own pollen. Many species of Sola­num ( potato, tobacco, etc .) and the tea plant are self-sterile because of genetic reasons. Cross-pollination is obligatory in such plants. Cucurbita - zucchini

10. (iii) Dichogamy : When stamens and carpels of a bisexual flower mature at different times, pollination between them becomes ineffective. Sometimes, however, it is found that self-pollination may take place at a later stage if cross-pollination fails.  Dichogamy may be of two types : - Protandry : The anthers ripen first as in most Compositae , many Umbelliferae , Malvaceae , etc. As a result, when the anther bursts, it pollinates stigmas of other flowers but not its own stigma which is not yet ripe. -Protogyny : The carpel matures first as in many members of Annonaceae (e.g., Annona, Polyalthia )and Magnoliaceae (e.g., Magnolia, Michelia ) as well as in Arum maculatum . When the stigma is receptive, its own pollen is riot ripe so that it has to depend on foreign pollens. Altomata procumbens protogyny Aeonium Protandry

11. 4.  Herkogamy ( herkos = barrier): In some flowers there may be some physical barrier between the anther and the style so that pollination between them is rendered difficult or even impossible. The male and female sex organs lie at some distance from each other. In some flowers corolla has peculiar forms which act as barrier in self pollination.e.g., Aristolochia . In some other flowers, the pollen are held together to form pollinia which can only be carried away by insects. e.g., Orchids and Calotropis . 5. Heteromorphism : In certain plants there are flowers of two ( dimorphic ) or three ( trimorphic ) different forms with anthers and stigmas at different levels. This dimorphism or trimorphism usually involves heterostyly (styles of different lengths) and heteroanthy (i.e., different types of anthers). Thus facilitate cross pollination. Some of them posses a long style but short stamens and are known as pin-eyed while other have short style and long stamens. These are known as thrum- eyed .e.g ., Oxalis .   Herkogamy

12. AGENTS OF POLLINATION

13. ABIOTIC AGENTS Non living methods Energy spent on pollen not on attracting pollinators By wind : Anemophily 98% of abiotic pollination Arose due to changes in environment and availability of pollinators Plant characteristics- specific height. Flowers are small, colourless , inconspicuous, nectar less and become arranged as inflorescence. The stigmas are large, hairy and feathery or branched to catch the air borne pollen grains. The anthers are well exposed for the easy dispersal of pollen grains. Pollen grains are small, light, dry, dusty, non-sticky and sometimes even winged. Example- Dandelions Dandelions

14. 2. By water: Hydrophily Rare, limited to 30 genera, mostly monocotyledons Uses water to transport pollen or whole anthers Plant characteristics- Flowers are small, colourless , inconspicuous, odourless and nectar-less and pollen grains and stigmas are generally unwettable ( algae, bryophytes and pteridophytes) . In Vallisneria , the female flower reach the surface of water- stigmas are long and sticky and pollen grains released- on surface of water- carried by the passive water currents In a majority of aquatic plants, the flowers emerge above the level of water and are pollinated by insects or winds as in land plants, e.g., water hyacinth and lily Other examples - Hydrilla and Zostera Vallisneria

15. 3. By rain : Used by small % of plants. Heavy rain discourages insect pollination and damage unprotected flowers. Mechanism - suitably adapted plants, such as  Ranunculus flammula and  Caltha palustris - excess rain drains allowing the floating pollen to come in contact with the stigma.  In rain pollination- orchid  Acampe rigida , the rain allows for the anther cap to be removed, allowing for the pollen to be exposed. After exposure, raindrops causes the pollen to be shot upward, when the stipe pulls them back, and then fall into the cavity of the stigma. This allows the plant to self-pollinate, which is useful when biotic pollinators in the environment have decreased. Acampe rigida

16. BIOTIC AGENTS Pollination involves pollinators/pollen vectors 100,000-200,000 species of animals act as pollinators By insects: Entamophily Major pollinating agent insects such as, bees, wasps and occasionally ants  Plant characteristics-Insect- pollinated flowers are large, colourful , fragrant, conspicuous and rich in nectar. The pollen grains and stigmas are sticky. Nectar + pollen grains = floral rewards insect pollinators. In some species, floral rewards = safe place to lay eggs, e.g., for the tallest flower of Amorphophallus (about 6 feet in height). In plant Yucca , moth and the plant, cannot complete their life cycles without each other. The moth deposits its eggs in the locule of the ovary and the flower, in turn plant gets pollinated by the moth. Yucca

17. 2. By vertebrates : zoophily pollination is performed by vertebrates such as birds and bats, particularly, hummingbirds, sunbirds, spiderhunters, honeyeaters, and fruit bats. Birds- ornithophil y- prefer plant with copious nector rich in carbohydrate and red petals. Bats - chiropterophily- prefer plants with white petals, strong scent and flower at night Reptiles- found in island system; predator pressure-reptiles become herbivorous- eat nector and pollen; e.g. Podarcis lilfordi Mammals- some rodents, bats and marsupials- The flowers are borne near the ground, are yeasty smelling, not colourful , and sunbirds reject the nectar with its high xylose content. The mice apparently can digest the xylose and they eat large quantities of the pollen.