1. Modified Flowers and Sexual Reproduction
Flowers II
Modified Flowers and Sexual Reproduction

2. Bracts Additional floral structures outside the calyx
May be leaflike or petal-like
The showy white or pink "petals" of dogwood are bracts

3. Tepals
Sepals are brightly colored and identical to the petals

4. Complete and Incomplete flowers
Flowers containing all four floral appendages are known as complete flowers
Flowers lacking any of the four floral structures are known as incomplete flowers
Flowers of grasses possess neither sepals nor petals

5. Perfect and Imperfect Flowers
Perfect flowers have both stamens and carpels
Imperfect flowers lack either stamens or carpels
Unisexual flowers
Male flowers called staminate
Female flowers called pistillate or carpellate

6. Plants with Unisexual Flowers
Monoecious plants have both male and female flowers on a single individual
Dioecious plants are either male or female with only unisexual flowers on a single individual

7. Ovary Position
Superior ovary - sepals, petals, and stamens are inserted beneath the ovary
Inferior ovary - sepals, petals and stamens are inserted above the ovary

8. Flower symmetry Regular flower displays radial symmetry
Irregular flowers display bilateral symmetry

9. Inflorescence Flowers grouped in clusters
Sometimes what appears as a single flower is actually an inflorescence
Sunflower, daisies, and dogwood flower common examples
The arrangement of flowers in the inflorescence varied with many patterns possible: spike, umbel, head, and catkin

10. Inflorescence Types
Spike Umbel Catkin Head

11. Sexual Reproduction in Flowers

12. Meiosis occurs: Stamens Carpels in pollen chambers of anther
in developing ovules in ovary

13. Pollen development -1
Microspore mother cells become distinct in the pollen chambers
Each MMC undergoes meiosis to produce 4 microspores
Each microspore develops into a pollen grain, the male gametophyte

14. Pollen chamber in anther

15. Pollen development - 2 Microspore nucleus undergoes mitosis to produce
generative nucleus
tube nucleus
Microspore wall modified into pollen wall
When mature pollen are released from the anthers

16. Pollen wall Intine - inner layer Exine - outer layer
Exine may be ornamented with spines, ridges, or pores

17. Pollen - Male gametophyte
Tube nucleus
Exine
Intine
Generative nucleus

18. Pollen Types
Ragweed Thistle Oak

19. Ovule One or more ovules develop within the ovary
Ovule is surrounded by integuments
Opening in integuments is known as the micropyle

20. Ovule development - 1
One cell becomes distinct as a megaspore mother cell
The megaspore mother cell undergoes meiosis to produce four megaspores
Three degenerate leaving one surviving megaspore

21. Ovule development - 2
Surviving megaspore undergoes three mitotic divisions to producing 8 nuclei
These 8 nuclei are distributed with 3 near the micropyle end of the ovule, 3 at the opposite end and 2 (polar nuclei) in the center
One of the nuclei at the micropyle end is the egg
This mature female gametophyte is often called the embryo sac

22. Ovule - Female Gametophyte
Polar nuclei
Integuments
Egg
Micropyle

23. Pollination Transfer of pollen from the anther to the stigma
Self-pollination - same flower
Cross- pollination - from one flower to another
Pollen transfer occurs mainly by animals or wind

24. Animal Pollinated Flowers
Flowers brightly colored and fragrant
Essential oils attract
Nectar produced
Color patterns may be nectar guides
Pollen larger, sticky, and not abundant

25. Wind Pollinated Flowers
Flowers small and inconspicuous often an inflorescence
Often lacking sepals and petals; no nectar
Pollen small, dry, light, and abundant
One ragweed plant can release one billion pollen grains (1 million tons/yr in NA)
Stigma
Ovary

26. POLLEN
Study of pollen called palynology has applications in many diverse fields: petroleum geology, anthropology, archeology, criminology, and medicine
When pollen is released by wind-pollinated plants, only a very tiny percentage reaches the stigma - remainder settles back to earth.

27. Pollen tube growth Pollen grain germinates on compatible stigma
Pollen tube begins growing down into the style towards the ovary
Generative nucleus divides mitotically producing two non-motile sperm.
Pollen tube continues to grow until it reaches the micropyle of an ovule

28. Pollen tube growth
Pollen
Pollen tube
Ovary
Ovule

29. Pollen tube growth
Pollen
Pollen tube
Sperm *
Ovary
Ovule

30. Double fertilization A distinctive feature of angiosperms
Both sperm involved in fertilization.
One sperm fertilizes the egg to produce a zygote
Second sperm fuses with the two polar nuclei producing the primary endosperm nucleus which develops into endosperm

31. Fertilization
Polar nuclei
Egg
Pollen tube
Sperm * *

32. Double fertilization Sperm + Egg -----> Zygote
Sperm + 2 polar nuclei > Primary
Endosperm Nucleus

33. Endosperm A nutritive tissue for the developing embryo.
Major food source for the human population
Endosperm reserves in wheat, rice, and corn are especially important food sources

34. Following fertilization
Sepals, petals, and stamens drop off
Ovary greatly expands becoming a fruit
Each fertilized ovule becomes a seed
Integuments of the ovule develop into the seed coat

35. Summary
1. Meiosis reduces the number of chromosomes from diploid to haploid
2. The flower is the unique reproductive structure of angiosperms
3. Pollination is the transfer of pollen from anther to stigma occurring through the action of wind or animals
4. In angiosperms reproduction is accomplished through the process of double fertilization.