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Chapter 22 Seed Plants I: Plants Without Flowers ("Gymnosperms")…

- - - - independent, heteromorphic generations
    - - new sporophyte
        
        while developing
        
        from the zygote
        
        is temporarily dependent
        
        on a tiny gametophyte
        
        for its start in life
        
        all genes are identical to
        
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        many new sporophytes perish
        
        half the genes are identical
        
        to maternal sporophyte
    - - would be advantageous if
        
        embryo could use
        
        photosynthetic and absorptive capacity
        
        of leaves and roots of
        
        previous sporophyte
        
        this happens by
        
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    - - moist sporophyll replaces
        
        moist soil
      - changes produced first
        
        seed plants, Division Pteridospermophyta
        
        and early members of Division Coniferophyta
  - - - Evolution of vascular cambium
        
        arisen independently in
        
        some lycophytes and equisetophytes
        
        cells could undergo
        
        radial longitudinal divisions
        
        allow cambium to grow
        
        in circumference as wood accumulated
        
        believe this type arose once
        
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  - - - plants produce small amount
        
        of very soft, spongy
        
        parenchymatous wood
      - includes cycads and their relatives
      - large, compound leaves
        
        and radially symmetrical seeds
    - - hard, strong wood
        
        with little parenchyma
      - small, simple leaves
        
        flattened seeds
      - occur in conifers and their relatives
  - - - these four are gynnosperms
    - - the flowering plants
- - - - gave rise to
        
        conifers
        
        cycads
        
        other gymnosperms
  - - - vascular cambium
        
        with unlimited growth potential and
        
        capable of producing both
        
        secondary xylem and secondary phloem
        
        was just as significant
        
        the wood was almost indistinguishable
        
        from conifers
        
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        contained elongate tracheids
        
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        little or no parenchyma
        
        rays were tall and
        
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  - - - Aneurophyton
      - Protopteridium
      - Proteokalon
      - Tetraxylopteris
      - Triloboxylon
      - Eospermatopteris
    - - and secondary growth
        
        primary xylem was
        
        protostele
        
        like rhyniophytes and trimerophytes
    - - ultimate branches
        
        resembled trimerophytes
  - - - abundant wood and secondary phloem
    - - had a siphonostele
        
        pith surrounded by ring of
        
        primary xylem bundles
        
        much like
        
        modern conifers and dicots
    - - sporangia terminal on
        
        short branches
        
        mixed with sterile
        
        leaf-like branch systems
      - megaspores released from sporangia
      - seeds not produced
- - - - because earliest seed ferns
        
        had three-ribboned protostele
  - - - of the stem differentiated
        
        as parenchyma
        
        not tracheids
        
        had ring of
        
        vascular bundles
        
        surrounding a pith
        
        an arrangement that occurs in
        
        stems of
        
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  - - - similar to
        
        gymnosperms and angiosperms
  - - - but were interesting differences
        
        tracheids were much longer
        
        and wide enough
        
        that several rows
        
        of circular bordered pits
        
        could occur on
        
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        rays were
        
        many cells wide
        
        were very tall
        
        being large wedges of parenchyma
        
        wood was manoxylic
        
        stem
        
        thick cortex that contained
        
        distinctive radial plates of
        
        sclerenchyma just below epidermis
        
        inner cortex contained
        
        secretory ducts
  - - - in overall organization
        
        large, compound, and planar
    - - the foliage leaves
        
        bore seeds
        
        within ovule
        
        megasporangium was large
        
        bundles of vascular tissue
        
        ran into and through it
        
        integument attached to it
        
        only at base
        
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- - - - moderate to gigantic size
        
        giant redwoods of California
        
        reach 90 m in height
        
        and 10 m in diameter
  - - - and never have
        
        bulbs or rhizomes
  - - - or scales
    - - persisting for many years
    - - just one or two
        
        long veins running down
        
        center of a
        
        needle-shaped leaf
      - several veins parallel
        
        in scale-shaped leaves
    - - tissue called transfusion tissue
        
        consisting of
        
        transfusion parenchyma cells
        
        intermixed with the tracheids
        
        forming a complex 3D pattern
        
        that facilitates transfer of materials
        
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        transfusion tracheids
        
        more or less cuboidal
        
        and have prominent
        
        circular bordered pits
      - endodermis
  - - - and phloem lacks sieve tubes
    - - that only one or two
        
        rows of circular bordered pits
        
        occur on radial walls
  - - - and pollen cones
        
        most of which are woody
        
        exception
        
        Juniperus and Podocarpus
        
        seed cones superficially resemble
        
        fruits of flowering plants
  - - - one main trunk
        
        bearing many branches
    - - composed of exclusively tracheids
      - rays are thin and tall
        
        contain both ray parenchyma
        
        and ray tracheids
      - resin canals
        
        produce thick, sticky pitch
        
        run vertically among tracheids
        
        and horizontally in rays
      - almost no axial parenchyma
      - phloem contains
        
        sieve cells and
        
        albuminous cells
        
        has tall, narrow rays
      - cork cambium
        
        produce thick,tough bark
        
        provides excellent protection
    - - tiny papery leaves
        
        occur on long shoots
        
        in their axils are
        
        short shoots
        
        produce long needle leaves
    - - pollen cones
        
        are simple cones
        
        with single short unbranched axis
        
        that bears microsporophylls
        
        microspore mother cells
        
        undergo meosis
        
        and from microspores
        
        then each of these
        
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      - seed cones
        
        more complex than pollen cones
        
        are compound cones
        
        each consisting of
        
        shoot with axillary buds
        
        short axis bears leaves
        
        called cone bracts
        
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        inside each megasporangium
        
        single large megaspore
        
        mother cell undergoes meiosis
        
        megasporangium does not dehisce
        
        megaspore retained inside
        
        grows into large coenocytic megagametophyte
        
        by free nuclear divisions
        
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        two or three
        
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- - - - ferns or young palm trees
        
        because they have
        
        stout trunks with
        
        pinnately compound leaves
  - - - and persistent leaf bases
        
        that remain on plant
        
        even after lamina and petiole
        
        have abscised
  - - - cycads are always dioecious
      - consist of spirally arranged
        
        shield-shaped microsporophylls
        
        that bear clusters of microsporangia
  - - - with an unusual distribution
        
        some occur in Cuba
        
        and Mexico
        
        some occur in Australia
        
        some occur in southeast
        
        Asia or Africa
        
        Distribution thought
        
        to have been widespread
- - - - very unusual
      - looks like
        
        large dicot tree
        
        with stout trunk
        
        and many branches
        
        but its wood
        
        like that of conifers
        
        it lacks vessels
        
        and axial parenchyma
      - has "broad leaves"
        
        but they have
        
        dichotomously branched veins
        
        like seed ferns
        
        not reticulate venation like dicots
      - have both
        
        short shoots
        
        which bear most
        
        of the leaves
        
        long shoots
      - Reproduction
        
        dioecious and gymnospermous
        
        but cones are not produced
        
        instead ovules occur in pairs
        
        at the ends of
        
        short stalk
        
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        pollen is produced
        
        in an organ
        
        that resembles a catkin
        
        having a stalk
        
        and several sporangiophores
        
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- - - - 30 species
      - mostly vines
        
        or small shrubs
        
        with broad leaves
        
        similar to dicots
    - - about 40 species
      - tough shrubs
        
        and bushes
      - leaves are reduced
        
        and scale like
    - - only species
      - have short, wide stem
        
        and only two leaves
        
        leaves grow perennially
        
        from basal meristem
    - - in being gymnosperms
        
        with vessels in their wood
      - may be related
        
        to primitive angiosperms
        
        however their vessel elements
        
        evolved from tracheids
        
        with circular bordered pits
        
        whereas angiosperms
        
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    - - compound and contain small bracts
    - - are compound and
        
        contain extra layer of tissue
        
        around ovules
        
        the tissue is variously interpreted
        
        as an extra integument
        
        bract
        
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