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Plants II

Plants II. THE SEED PLANTS I. The Vascular Plants. Hypericum sp. Photo by Alan Mulvey. Gymnosperms. Evolution of the Seed Plants. Heterosporous Seed: (embryo & stored food) Evolution of pollen Megagametophyte develops within ovule * Microgametophyte develops within pollen grain *

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Plants II

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  1. Plants II THE SEED PLANTS I The Vascular Plants Hypericum sp. Photo by Alan Mulvey Gymnosperms

  2. Evolution of the Seed Plants • Heterosporous • Seed: (embryo & stored food) • Evolution of pollen • Megagametophyte develops within ovule* • Microgametophyte develops within pollen grain* • Pollen grains evolved by reduction of male gametophyte & protection by pollen walls • Both the male & female gametophytes were retained within the sporophytes

  3. Evolution of the seed • One cell megaspore is retained within megasporangium • It is protected by integument • It develops into mature megagametophyte within the embryo sac • After fertilization, it matures into the embryo (sporophyte)

  4. Generative cell (2 sperms) Tube cell Pollen wall Lilium: Pollen

  5. Generative cell Tube cell Wings Pine: Pollen

  6. Evolutionary transition from a gametophyte to sporophyte dominance From Keeton, 1993

  7. The Gymnosperms: Characteristics • (naked seed)* • Water is not required for fertilization • Mainly pollinated by wind • Reproductive changes increased protection of gametes • Have sunken stoma & thicker cuticles

  8. Two Seeds per Scale Cone Scale Seed Cone

  9. Epidermis Hypodermis Sunken Soma Pine: Leaf

  10. Characteristics Cont.. • Have secondary growth - all trees or shrubs • Mostly evergreen • Xylem has tracheids, lacks vessels (except some Gnetophytes) • Phloem has sieve cells, lacks sieve tube members

  11. Progymnosperms • An extinct group that arose in late Paleozoic • Intermediate between seedless & seed plants • Progymnosperms were ancestors of seed plants • Evolved bifacial V.C. & wood (page 411)

  12. Seed Plants I - Gymnosperms • Conifers – Coniferophyta • Cycads – Cycadophyta • Maidenhair tree – Ginkgophyta • Gnetophytes – Gnetophyta

  13. Conifers: Phylum Coniferophyta • evolved 290 MYO • Constitute the largest group of gymnosperms (50 genera, 550 spp.) • Include the tallest & largest trees ever (Giant redwood) • Conifers (pine, fir, spruce) have great commercial value in temperate zones • Leaves are either • needles, long or short, as in pines, fir, spruce • small flat, scale-like as in junipers, cypresses • Mostly evergreen, monoecious

  14. White Pine: Pinus strobus

  15. White Pine

  16. White Pine : Twig &Needles

  17. Pollen Cones Seed Cone White Pine

  18. Longleaf Pine: Pinus palustris

  19. Loblolly Pine: P. taeda

  20. Loblolly Pine: Pollen Cones

  21. Turpentine Production Slash Pine: P. elliottii

  22. Bald Cyprus Knees: Taxodium distichum Knees

  23. Bald Cyprus

  24. Bald Cyprus

  25. Bald Cyprus: Crown & Seed Cones

  26. Coast Red Wood: Sequoia sempervirens Fossil

  27. Sequoia: Coast Red Wood

  28. Giant Red Wood Sequoia http://www.habitas.org.uk/gardenflora/sequoiadendron.htm

  29. Seed Cones Pollen Cones Giant Red Wood http://www.conifers.org/cu/se2/

  30. Balsam Fir: Abies balsamea

  31. Leaves Balsam Fir Seed Cone

  32. Larch: Larix decidua

  33. Larch Developing cones

  34. Common Juniper: Juniperus communis Leaves Tree

  35. Juniperus virginiana (Eastern Red Cedar) Cones

  36. Hemlock:Tsuga canadensis

  37. Hemlock: Leaf & Cone

  38. White Spruce: Picea glauca

  39. White Spruce Pollen cones Young seed cones Pollinated seed cones

  40. Pacific yew: Taxus brevifolia http://www.fw.vt.edu/dendro/dendrology/syllabus/tbrevifolia.htm

  41. Maidenhair tree Phylum Ginkgophyta: • One extant species, Ginkgo biloba (notched leaf)* • Reproduction is dioecious • Ginkgo is resistant to air pollution (city parks) • Pickled seeds are eaten in Asia • Ginkgo is now cultivated, could be in the wild (Asia)

  42. Ginkgo biloba Leaves are broad with dichotomous venation

  43. The Ginkgo tree has properties which make it resistant to nuclear radiation. This tree survived the Hiroshima bombings. www.ginkgo.co.nz/images/ large/ginkgotree.jpg

  44. Ginkgo biloba

  45. Male cones Sperms are flagellated, borne in cone-like structure

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