pollination - process by which pollen is placed on the stigma

• can by carried by wind, animals, or flower itself
• early seed plants pollinated by wind
  • large quantities of pollen shed, blown about
  • must grow close together to work efficiently
  • pollen travels less than 100 meters
• earliest angiosperms pollinated by insects
• bees - pollinates the majority of insect-pollinated angiosperms
  • tend to visit blue/yellow flowers
  • locates food first by odor, then by shape/color/texture
  • use nectar as food for adult bees
  • uses pollen as food for developing larvae
  • mostly solitary
• insect pollinators other than bees
  • butterflies - perch on the landing platforms of phlox flowers
  • target heavily scented flowers (easier to find in the dark)
• birds - especially hummingbird/sunbird
  • targets flowers w/ lots of nectar (not attractive to insects)
  • attracted by the red color
• wind-pollinated angiosperms have small/greenish/odorless flowers
  • reduced/missing corolla

self-pollination - mostly in flowers w/ small flowers in temperate regions

• don’t need pollinators to produce seed >> uses less energy, able to grow where animals are scarce
• creates more uniform populations
• outcrossing - necessary for adaptation/evolution
  • dioecious plants - produce only ovules or pollen, cannot self-pollinate
  • monoecious plants - produce both ovules/pollen, must produce gametes at different times to prevent self-pollination (dichogamous plants)
  • self-incompatibility >> locus prevents self-pollination, pollen tube gets blocked

angiosperm double fertilization - creates fertilized egg, endosperm to nourish embryo

• pollen tube - grows after pollen adheres to stigma
  • pierces the style
  • reaches embryo sac >> nuclei around egg cell disintegrates >> tube tip enters egg
  • tube tip bursts >> 2 sperm cells released (1 fertilizes egg to form zygote, other forms w/ polar nucleus to form triploid endosperm)
• endosperm completely transferred to cotyledons in dicots (disappears after maturing)
• seed enclosed in fruit