Pollination • Occurs when pollen reaches the stigma • 2 types—cross-pollination and self-pollination • Cross-pollination—pollination by a different individual • Self-pollination—pollination by the same individual • Self-pollination has similar results as asexual reproduction • Cross-pollination is similar to reproduction in animals, in that it: • insures the mixing of genetic material • insures genetic diversity
Mechanisms to Insure Cross-pollination • Stamen and Style mature at different times • Stigma and pollen are incompatible—stigma prevents pollen growth if it’s from the same plant • Monoecious and Dioecious species • Monoecious (“one house”)—male / female flowers on the same plant • Example = corn • Dioecious (“two houses”)—male / female flowers on different plants • Example = dates, willows
Animals and Pollination • Wind pollination is inefficient and “expensive” • Angiosperms and insects begin association 120 mya • Angiosperms and Insects evolved together—co-evolution • Plants developed flowers that attracted pollinators • Insects developed body parts to reach nectar • Some flowers developed bilateral symmetry to match the pollinator • Co-evolution also occurred with birds and bats • Some bizarre adaptations for pollination can be found at:http://www.life.uiuc.edu/plantbio/260/Attenborough1.pdf • Other animals can also pollinate: • Birds, bats, etc.
Some plants developed to protect the ovary from damage by animals. • The bases of the stamens, petals and sepals fuse around the ovary, and the “flower” begins above the ovary. • This is an “inferior ovary” • Some did not develop this way, and the ovary is above the petals, sepals and stamens. • This is a “superiorovary”.
How fertilization happens (angiosperms) • Pollen arrives on the stigma • Pollen begins to grow into the pistil • This creates a “pollen tube” that reaches the ovary • The gametes move down this tube • Gametes fuse with the ova to form a zygote • The zygote develops into seed that will grow into the sporophyte
Seed Dispersal (and examples)—the “big 5!” • Wind (Dandelion) • Water (Coconut palm) • Thrown from the parent plant (Poppy) • Attaches to an animal and is carried away (Beggars Lice, Cockle bur) • Eaten by animals and deposited elsewhere (Apple)
Fruit Development • Ovary develops into a fruit that contains the seed(s) • Flower parts may persist (apple) or die and fall off (orange) • Fruits have 3 distinct layers • Exocarp—outermost layer (skin or peel) • Mesocarp—middle layer (flesh) • Endocarp—inner layer (pit or stone) • Pericarp = exocarp + mesocarp + endocarp
FRUIT TYPES • FLESHY FRUITS • Berry—all 3 layers (exocarp, mesocarp, endocarp) are soft • Grape, Tomato • Pome—similar to berry, but endocarp is papery or leathery • Apple • Drupe—similar to berry, but endocarp is hard • Peach, Cherry, Plum • Pepo—fleshy but the exocarp is a tough, hard rind; inner tissues may not be distinguishable • Pumpkin, Squash • Hesperidium—exocarp is leathery • Orange, lemon, lime
Dry FruitsIndehiscent (not opening up at maturity) • Caryposis—small, simple. Seed coat fused to fruit • Grasses: rice, oats, wheat, corn • Achene—like caryopsis, but seed and fruit are distinct. Fruit wall is papery • Sunflower • Samara—one seed fruit with wing like outgrowths • Maple, ash, alder • Nut—pericarp is hard • Walnut, pecan, almond • Dehiscent (does open up at maturity) • Legume—fruit breaks along both sides • Beans, peas • Follicle—fruit breaks open on one side • Columbine, milkweed • Capsule—opens many ways • Primrose, poppy, iris
Compound Fruits • Aggregate fruit—carpels of flower NOT fused but grow together during fruit maturation • Raspberry, blackberry • Multiple fruit—all the fruits grow together during maturations • pineapple