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Lecture 10: flowers, pollination and fertilization (Type of flowers…

- - - - Insects
        
        Flowers attracts insects by color
        
        Sepals of Mussaenda modified to colored leaf
        
        Bracts of bougainvilleas highly colored and attractive
        
        Spathes in banana are brightly colored
        
        Head/ capitulum of sunflower consisting of many small florets
        
        Nectar
        
        Produced by a special gland (Nectary) or in sac or tube-like structure (Spur)
        
        Found at the base of one of the floral whorls
        
        Scent
        
        Nocturnal flowers emit sweet scent
        
        Or Stinking smell to attracts flies
        
        Pollen grains sticky or spiny
        
        Stigma sticky
        
        Pollen grains provide food
        
        Shelter for insects from rain and sun
      - Animals
        
        Birds, squirrels, bats and snails, etc.
      - Wind
        
        Small and inconspicuous flowers
        
        Do not emit scent or nectar
        
        Produce large amounts of pollen grains that are light, dry and with wings
        
        Stigmas comparatively large & protruding, sometimes branches and often feathery
      - Water
        
        For e.g. Vallisneria
        
        Minute male flowers get detached from the male plant and float on water
        
        Female flowers on a long stalks brought to the level of water
        
        On contact, the anthers burst and pollen grains are distributed on the stigma
        
        After pollination, the stalk of the female flower becomes closely coiled and the fruit develops under water
- - - - Vegetative/ tube nucleus
      - Generative nucleus: divides to give 2 male gametes