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Reproduction and growth among different plant types., Life on land! -…

- - - - except for moss and liverwort.
- - - - 2 taxa share same trait due to common ancestor.
    - - derived novel trait.
      - a plant can have a similar trait to something else, but their existences can be unrelated.
    - - 2 taxa show the same trait due to similar evolutionary pressure.
    - - character older than
  - - - can continuously divide mitotically to create new tissue.
    - - ancestral trait to ALL land plants.
    - - creates physical copy of itself.
      - mitosis review!!!!
        
        prophase
        
        metaphase
        
        anaphase
        
        telophase
        
        cytokinesis
    - - bryophytes protonema is filamentous and has an apical bud.
      - charophytes mainly filamentous
        
        switch from 2d growth to 3d growth
        
        filamentous algae grow in one direction, in a single plane.
        
        later on, cells are not only arranged linearly.
        
        cytokinesis in oblique planes required.
        
        causes leafy shoots in all directions.
        
        bifurcating sporophyte
        
        split shoot tip into two groupings of meristematic tissue.
        
        apical meristem separated into two
        
        bifurcation evolves from having a single stem.
        
        terminal sporophyte replaced
        
        new development!
        
        sporangia moved
        
        becomes side axis, bifurcation happens
        
        1 more item...
        
        on leaf!
        
        necessary prior to indeterminacy.
        
        new development 2
        
        bifurcating branches
        
        evolved prior to vascularization.
        
        equal branching = isotomous
        
        unequal branching = anisotomous
        
        lycophytes vary in shape and structure.
        
        new development
  - - - produce new organs
      - from shoot apex
      - produce new tissue
    - - multi-stemmed, dominant individuals
    - - vascular plant sporophyte
        
        vascular plant meristems may have evolved indepenendantly.
        
        lycophytes
        
        monilophytes
        
        spermatophytes
        
        selective pressure for independent evolution of independency
        
        shoot apical meristem
        
        totipotent region
        
        matures into transition tissues
        
        ground meristem
        
        procambium
        
        protoderm
        
        divides continuously
      - fern
      - bryophyte gametophyte
- - - - Roots draw water from the soil towards the stem
      - Bark protects xylem that transports water from roots upwards.
      - Photosynthesis needs water.
      - Once done, water leaves through stomata. Keeps forests cool.
    - - Evaporation of water from stomata of leaves.
      - Major drivers to water cycle.
      - Huge amounts of transpiration.
        
        Some plants release gallons upon gallons of water per individual.
      - Happens due to water free energy.
        
        Potential for water to move
        
        Due to water polarity.
        
        Attracted to other substances
        
        Lower potential to move when surrounded by ions.
        
        Hypo to hyper solutions, until equilibrium.
        
        Water potential
        
        Based on the free energy of water.
        
        Water moves from less negative water potential to areas of more negative water potential.
        
        Higher pressure pulls water out of the plant. You cannot pull too much or you will cause boiling.
        
        Peaks in water potential at night, dip during mid-day.
        
        There is a permanent wilting point in which after a certain amount of water deprivation, nothing can save the plant.
        
        Components of water potential
        
        Ψp = pressure potential
        
        If water is under pressure, both pressure potential and water potential increase
        
        Effect that turgor pressure has on Ψ
        
        Hydrostatic pressure exerted on water in a cell
        
        In turgid plant cells positive value
        
        Xylem cells negative due to cohesion
        
        Water at atmospheric pressure has a pressure potential of zero.
        
        Ψ(pi) = osmotic potential
        
        Effect that solutes have on Ψ
        
        Adding salutes decreases water's free energy, so Ψ(pi) is always negative
        
        Ψm = matric potential
        
        Adhesion to structured such as cell wals, membranes, and soil particles.
        
        Adhesion can only decrease water's free energy, so Ψm is always negative.
        
        Significant only outside living systems in very dry soils.
- - - - Diploid
        
        Meiosis
      - Alteration of generations
        
        Multicellular haploid stage (gametophyte)
        
        Forms gametes
        
        Gametes form zygote by syngamy
        
        Sperms forms in antheridium
        
        Egg forms in archegonium
        
        Formed by 4 haploid spores
        
        Multicellular diploid stage (sporophyte)
        
        Sporophyte embryo is formed by zygote
        
        It's all a cycle and it all connects in a circular motion.
      - Gametophytes dominant in early land plants
        
        Example: liverwort.
        
        Let's talk about marchantiophyta liverwort.
        
        Dominant leafy gametophyte.
        
        Temporary diploid sporophyte
        
        Parasitic, not helpful.
        
        Located in archegoniophore
        
        Spores are released from the umbrella structure on these.
        
        Spores become gametophytes.
        
        1 more item...
        
        Meiosis forms haploid spores
        
        Bryophyta #
        
        Mnium moss
        
        Dominant leafy gametophyte
        
        Temporary diploid sporophyte
        
        Zygote undergoes mitosis to form the multicellular diploid stage. Dependent on gametophyte.
        
        Sporophyte has sporangium. Spores formed by meiosis here.
        
        Spores form gametophytes.
        
        1 more item...
      - Sporophyte dominance evolves over time.
        
        Example: trees
        
        :
        
        This image is horrible but it gets the point across?
        
        Let's talk about selaginella.
        
        Heterosporous; different spores sizes.
        
        Gametophyte is retained inside spore wall.
        
        Sperms must still swim to egg.
        
        Germination happens entirely in the spores wall of gametophyte.
        
        Cell wall breaks open to release sperm
        
        Sporophyte
        
        Strobilli on sporophyte contains sporangia.
        
        Microsporangia contains male spores
        
        Microspores are also dispersed.
        
        Microspores undergoes mitosis
        
        Megasporangia contains female spores
        
        1 megasporocyte undergoes meiosis to form 4 megaspores.
        
        1 more item...
        
        Megaspore develops mitotically
        
        1 more item...
        
        Monilophyta
        
        Polypod fern example
        
        Independent gametophyte
        
        Independent sporophyte
        
        Diploid tissue that we consider as most of the plant.
        
        Sporophyte is large.
        
        Zygote undergoes mitosis to form multicellular diploid stage
        
        Ferns often have gatherings of sporangia, known as sori.
        
        Sometimes covered by indusium, for protection.
        
        Within sporangia, meiosis forms spores. Spores are dispersed.
        
        Spores form multicellular haploid stage.
        
        Gametophytes. #
        
        3 more items...
      - As mentioned before, algae ancestor.
        
        Thought to be haplontic.
        
        Haplontic life cycle includes zygote, gametes, and multicellular haploid individuals.
      - Antithetical theory
        
        Suggests sporophyte was inserted into haplodiplontic life cycle of green algae.
        
        The sporophyte first arrives when the zygote didn't immediately undergo meiosis.
        
        Happens when zygote undergoes a period of replication through mitosis instead.
        
        Multicellular diploid stage.
        
        Over time this was chosen to become physiologically independent. Became dominant.
        
        Predictions
        
        Earlier generations would have been heteromorphic.
        
        Sporophyte is short lived and simple
        
        Gametophyte is persistent anf relatively complex
  - - - guard cells
        
        closing/opening is an active metabolic process.
        
        aids in building turgor pressure
        
        potassium is pumped in and out.
        
        in = open
        
        out = closed
        
        surround pore into leaf. they control the opening.
        
        photosynthetic dependent.
        
        closure at night or under water stress.
        
        photosynthesis provides potassium for the proton pump. #
        
        potassium in, protons out.
        
        ancestral condition filled with chloroplasts.
        
        independent of blue light
    - - earliest features of land plants
      - present in all land plants, besides liverwort, probably due to trait loss.
      - earliest fossil evidence
        
        Early Devonian sporangia.
        
        similarities in old fossils compared to extant angiosperms
        
        evidence of air chambers
        
        bean-like shape
        
        inner wall thick
      - stomata probably originally aided in desiccation of sporophyte.
        
        probably not regulated like it is now.
        
        not aiding in gas exchange really.
        
        stomata mainly located on sporophyte to help dry it out.
        
        aided in spore disperal.
        
        lower stomatal frequency
        
        support the idea that the original role of stomata was different than it is now.
        
        was present on non-photosynthetic sporophyte tissue in the early lineages.
        
        extant early lineages generally have stomata that don't close.
        
        intercellular space
        
        psuedostomata
        
        open pores with no empty space
        
        hypodermis/liquid fills space
        
        stomatal canal
        
        small air space
        
        for diffusion of minerals
    - - monocots and eudicots have diverse forms of stomata.
        
        eudicot - random dispersion
        
        kidney bean shape
        
        monocot - same direction as epidermal cells.
        
        dumbbell shape
    - - amount of water loss to carbon gain
      - ABA responsive in seed plants.
        
        as ABA increases, stomatal size decreases. pore closes.
        
        pore closes during water stress,
        
        derived characteristic. complete 180 of function how it used to function.
        
        reduces amount of water loss
        
        maintains hydration
        
        being responsive to drought helps to survive, for plants.
      - prevents cavitation.
      - conductants increase during stress periods.
      - angiosperms can open and close stomata depending on how dry the air is.
        
        vapor pressure deficit.
  - - - constraints/limitations early on
        
        high global temperatures :hot_pepper:
        
        low stomatal density
        
        low capacity for water uptake, before root evolution
        
        BAD VASCULAR TRANSPORT IN LEAVES, too much energy, too hot.
        
        LEAF HOT. BURN. :fire:
        
        if not burn, embolism :frowning_face:
      - polyphyletic origin
        
        earliest evidence for true leaves
        
        lycophytes
        
        lycophylls/microphylls
        
        mitosis of 2 epidermal cells
        
        lycophyte
        
        just like with roots.
        
        euphyllophytes
        
        independent evolution
      - optimal light interception
        
        indeterminate growth proceeded leaf growth #
        
        leaves initiated in regular patterns around stem
        
        leaves optimized light interception for the purpose of photosynthesis.
      - convergent evolution
        
        leaves had at least 5 independent origins
        
        liverwort gametophyte #
        
        developed from mitosis of a single cell
        
        moss - midvein cell layer
        
        moss gametophyte #
        
        lycophyte sporophyte
        
        monilophyte sporophyte
        
        fern fronds
        
        mitosis of a single apical cell
        
        shoot-like development
        
        spermatophyte sporophyte
        
        pool of recruited cells from the apical meristem, to give rise to those organs.
      - theories
        
        enation theory
        
        elaboration of epidermal outgrowth.
        
        sporangia no longer at tip.
        
        flap of tissue at stem moves to axis, is supported by axis, and is referred to as sporophyll because it has the sporangium sitting on it.
        
        obtains vascular strand at some point, which is attached to the xylem.
        
        there IS consistent fossil evidence for this development.
        
        explanation for how lycophyte leaves formed.
        
        Zimmerman telome theory
        
        explains evolution of euphylls
        
        overtopping
        
        unequal branching. main branch, and side branch
        
        planation
        
        flattening of axes into 2 dimensional
        
        webbing
        
        4 more items...
    - - chlorenchyma
        
        specialized parenchyma containing chloroplasts
        
        mainly for photosynthesis
        
        ground tissue
      - aerenchyma
        
        ground tissue
        
        specialized parenchyma that contains air spaces caused by cell digestion.
        
        meant for gas exchange, and occasionally, buoyancy.
      - collenchyma
        
        found in bundle sheath of veins of some species.
        
        celery strips stuck in teeth? that's collenchyma.
        
        ground tissue
        
        thickened primary cell walls
        
        mainly function for flexible support
      - vascular tissue
        
        xylem #
        
        tracheids
        
        water transport
        
        phloem #
        
        sieve tube elements/sieve cells
        
        companion cells/albuminous cells
        
        photosynthate transport
        
        in veins
      - epidermis
        
        dermal tissue
        
        epidermal cells
        
        guard cells
        
        often cutenized
        
        mainly function to protect internal tissues
    - - lycophylls
        
        microphylls
        
        single vascular trace along center of blade
        
        vascular strand connects directly to stem
        
        mesophylls, stomata, epidermis
      - monocot leaf
        
        epidermis
        
        adaxial (outer)
        
        abaxial (towards stem)
        
        covered by cuticle, contains stomata, bulliform cells
        
        good for rolling and unrolling the leaf in response to drying and whatnot.
        
        mesophyll
        
        filled with chloroplast-filled cells
        
        veins
        
        surrounded by bundle sheaths,
      - eudicot leaf
        
        epidermis
        
        dermal tissue
        
        epidermis cells, guard cells
        
        upper and lower epidermal cells, cuticle
        
        mesophyll
        
        palisade, functions for photosynthesis
        
        upper part of leaf, filled with chlorenchyma, very tightly packed.
        
        spongy
        
        lower, filled with air pockets, works for gas exchange.
        
        veins
        
        bundle sheath cells
        
        xylem on top, phloem on bottom
  - - - group of plants that have vascular tissue are called tracheophytes.
        
        note that bryophytes are non-vascular and aren't included in the tracheophytes.
        
        everything to the right of bryophytes are vascular plant groups.
        
        tracheophytes have synapomorphy. #
        
        all have vascular tissue.
        
        very diverse vascular architecture.
    - - in cooksonia, there is fossilized annular thickenings, thought to be evidence of tracheids.
        
        early tracheids
        
        water transport ONLY. no support
        
        lignified, long and wide.
        
        different traits develop over time.
        
        true tracheids
        
        likely evolved once; synapomorphic
        
        single celled conduits, lignified with ornamented walls.
        
        tapered ends, sort of narrow.
      - lycophytes
        
        early vascular group
        
        created towering forests during Carboniferous
    - - critical to land plant success.
      - early land plants were poikilohydric
        
        water content changes with moisture in the environment.
        
        likely to depend on water storage.
        
        able to equilibrate water potential through environmental source.
        
        stayed small to reduce need for water.
      - earliest water conducting cells
        
        hydroids
        
        used by bryophytes.
        
        NO plasmodesmata.
        
        aid in refilling from cavitation.
        
        this is necessary on small scale. large plants cannot do this.
        
        apomorphic trait to true vascular tissue. #
        
        no lignin.
      - tracheary elements of xylem
        
        die at maturity
        
        to form long hollow strands to improve water flow.
        
        thickened lignin walls.
        
        structural support
        
        waterproofing
        
        allows shift from hydrostatic support to a lignified cell wall support.
        
        through primary growth
        
        first achieved through evolution of sclerenchyma tissue.
        
        eg. fibers,
        
        over time the lignin was likely used to help prop the inner cells open under negative pressure.
      - vessel element differentiation
        
        apical meristem #
        
        vacuolization
        
        elongation
        
        secondary cell wall
        
        annular
        
        helical
        
        reticulate
        
        porous
        
        dead at maturity.
    - - bryophytes
        
        no vascular tissue in very early land plants.
        
        food conducting cells
        
        specialized plasmodesmata in end walls.
        
        alignment along longitudinal arrays of endoplasmic microtubules.
        
        plastids, mitochondria, ER vesicles.
        
        breakdown of tonoplast
        
        mix vacuolar and cytoplasmic contents.
        
        occasional nuclear breakdown.
      - sieve cells and albuminous cells
        
        only gymnosperms
        
        only type of phloem cell that gymnosperms have. no sieve tube element.
        
        sieve cells always accompanied by albuminous cell.
        
        albuminous cell = specialized parenchyma cell.
      - sieve tube elements
        
        distinguishable from sieve cells by sieve plates.
        
        filled with sieve pores.
        
        usually on end wall.
        
        callose formation near sieve pores in maturity
        
        thought to fill pores when injury detected.
        
        prevent infection by causing pores to close.
        
        limits damage done to phloem cells.
        
        many sieve tube elements together = sieve tube
        
        made up of primaru cell wall.
        
        protoplasts are alive at maturity unlike in xylem. #
        
        they have to be alive to function.
        
        very few cells are endoplasmic reticulum.
        
        sieve tube elements and companion cells have many unique features.
        
        companion cells
        
        next to each sieve tube element
        
        has more organelles than sieve tube elements.
        
        highly connected through plasmodesmata.
        
        both came from same mother cell
        
        tons of plasmodesmata allowed to form between them.
        
        very necessary for function of sieve tube. sieve tube will die without companion cell.
        
        one pore in sieve tube branched into many on companion cell side.
        
        sieve tube element
        
        no nucleus
        
        few organelles
        
        pretty hollow.
        
        i think of them like a factory worker and a machine. the factory worker being the companion cells, and the machine being the sieve tube element.
        
        contents
        
        p proteins
        
        may help in plugging pores in response to leakage.
        
        forisomes
        
        legume plants only
        
        basically a p protein but it forms a different shape and only functions to plug pores.
        
        sieve element plastids
        
        we don't really know what it does at this time.
        
        mitochondria, though very few.
        
        lil spikes on mitochondria to keep stuff anchored while photosynthate is flooded through the sieve tube.
        
        endoplasmic reticulum
        
        lost ribosomes.
        
        highly folded
      - phloem differentiation
        
        primary cell wall thickened
        
        where sieve plates would be
        
        cytoplasmic clearing
        
        no ribosomes
        
        callose deposited around terminal plasmodesmata
        
        nuclear breakdown
        
        formation of sieve plate and pores.
        
        nucleus is eaten.
    - - Arrangement changes within a plant
        
        Root and shoot have different arrangements
        
        Key features to eudicots and monocots
        
        Monocot
        
        Root with pith
        
        Stem without pith
        
        Eudicot
        
        Root system without pith
        
        Stem with pith
      - Increasing complexity
        
        Stem diameter increased
        
        Plant height increased
        
        Led to
        
        Compartmentalization
        
        Selected for a woody habit.
      - Major stele types
        
        Protostele
        
        Earliest
        
        Solid vascular strand
        
        Phloem surrounds xylem or interspersed
        
        Lycophytes
        
        Exarch
        
        Siphonostele
        
        Ring of phloem, xylem, surrounding pith
        
        Ferns
        
        Endarch
        
        Eustele
        
        Most complex
        
        Strands of phloem and xylem separated by parenchyma
        
        Progymnosperm
        
        Eudicotyledonae
        
        Endarch
      - Archs
        
        Based on xylem maturation
        
        Protoxylem
        
        1st xylem to mature
        
        Smaller in diameter
        
        Metaxylem
        
        Develops later
        
        Usually larger diameter cells
        
        Exarch
        
        Protoxylem outside metaxylem
        
        Eg. Protosteles
        
        Endarch
        
        Protoxylem in middle
        
        Eg. Eusteles, atactosteles
        
        Mesarch
        
        Protoxylem surrounded by metaxylem
        
        Eg. Siphonosteles
    - - Environmental change
        
        Amount of water loss per carbon gained increased after Silurian
        
        Carboniferous period greatly drained atmospheric CO2
        
        Water demand relatively high
        
        Minimal maintenance = cell death
        
        Transport energy minimal
        
        Water filtration close to soil access
        
        Loss of secondary growth
        
        Monocotyledonae
        
        Arborescent growth still present
      - Selection pressure for wood
        
        Increased competition for light selected for
        
        Taller plants, more developed tree canopies
        
        Higher rates of transpiration
        
        More xylem, wider xylem and longer conduits
        
        Likely evolved 5 times
      - First tree (featuring ECU'S archaic tree!)
        
        Lepidodendroids
        
        Carboniferous
        
        ~320 mya
        
        Vascular cambium only divided internally
        
        Archaeopteris
        
        Devonian/Carboniferous
        
        Reproduced via spores + leaves funny
        
        Extant lineages
        
        Lycophytes
        
        Euphyllophytes
      - Secondary growth
        
        Complex plant development
        
        Growth in girth
        
        Produce secondary...
        
        Xylem (wood)
        
        Phloem (inner bark)
        
        Ground tissue (rays)
        
        Continous circular ring growth
      - Vascular cambium
        
        Fusiform initials
        
        Stem cells
        
        Xylem and phloem
        
        Fascicular cambium
        
        Fusiform - longitudinal
        
        Ray initials
        
        Stem cells
        
        Ray cells
        
        Interfascicular cambium
        
        Ray - radial
        
        Pericardial division = more xylem and phloem
        
        Anticlimactic division
        
        Wider circle of vascular cambium
        
        :
        
        Annular rings
        
        Xylem secondary cell walls robust
        
        Phloem crushed :(
        
        Ring width determined by season and environment
        
        Alteration of early wood and late wood
        
        Sapwood vs heartwood
        
        Sapwood
        
        Water transport
        
        Newer
        
        Heartwood
        
        Functions in storage
        
        Can't transport water
        
        Older
        
        Hardwood vs softwood
        
        Softwood
        
        Tracheids only
        
        Little room for fibers
        
        Gymnosperms, evergreens, eg. Pines
        
        Hardwood
        
        Vessel elements' efficiency allow space for fibers
        
        Angiosperms, deciduous, eg. Oak
      - Plant armor
        
        Periderm
        
        Phellem, cork
        
        Phellogen, cork cambium
        
        Phelloderm
        
        Outer bark and inner bark
        
        Inner bark = phloem and cortex
        
        Outer bark rougher
  - - - Early roots branched at tip.
    - - But we aren't worried about that.
    - - early plants needed anchorage due to frequent flooding issues.
        
        anchorage and limited mineral uptake provided by rhizoids.
        
        uni-multicellular projections.
        
        genes
        
        predate land plants
        
        play role in root hair development.
      - early evidence of true roots found in lycophytes.
        
        assembly of the rhizoids changed and evolved over time and bifurcated to form true roots. we can see this in extant lycophytes.
      - rhizomorphs
        
        seen in extinct trees, lipidodendrales
        
        dichotomous rooting system.
        
        lateral stigmarian rootlets.
        
        root hairs, mixed reports
        
        highly branched
        
        similar to roots.
        
        no chlorophyll
        
        waste of resources since roots don't face the light. no need for chlorophyll.
        
        no stomata
        
        develop gravitrophically.
        
        no root cap
        
        extant species? lycophytes
    - - started growing laterally to support the plant's body to prevent it from falling.
      - early Devonian
      - upright stem, prostrate stems, downword stems.
      - root transition
        
        early without root hairs, and an intact epidermis that covered the root tip.
        
        anticlinal divisions only.
        
        Devonian lycophyte
        
        independent evolution of endodermis and root cap.
        
        root meristem
        
        diversity of arrangement used to infer phylogeny.
        
        number of initial cells differ.
        
        similar genes across plant taxa.
        
        similar genes in shoot to root.
    - - Primary root
        
        Derived from radicle
        
        Main root
        
        Mainly dominant in eudicots
        
        Many ephemeral in monocots
        
        Two "most important" roots
      - Lateral roots
        
        Adventitous roots
        
        Derived from stems and levaes
        
        Dominant in monocots
      - Seminal roots. Derived from mesocotyl
      - General root plan
        
        Highly differentiated multicellular axis
        
        Found only in sporophytes of vascular plants
        
        What do they do?
        
        Anchors plant body to substrate
        
        Absorbs water
        
        Absorbs dissolved minerals
        
        Common features
        
        Apical meristem and root cap
        
        Apical meristem
        
        Quiescent center
        
        Rarely divides
        
        Backup plan
        
        Maintains initial cells
        
        Behind root cap
        
        Root cap
        
        Evolves independently
        
        Lycophytes, euphyllophytes
        
        Protect underlying tissues
        
        Cells that slough off
        
        Pericycle
        
        Just inside the endodermis
        
        Initiation of lateral root development
        
        Pluripotent
        
        Cells can turn mitotic.
        
        Endodermis
        
        Prevents apoplasmic water movement
        
        Casparian strip
        
        Forces water to move through cell membranes and be filtered.
        
        Efficient way for water to move but doesn't protect against disease on its own.
        
        Root hairs
        
        Zone of differentiation
        
        Single celled
        
        Major absorption of water and minerals via osmosis from hypotonic soil solution.
        
        Delicate and short lived.
        
        So to maintain, root tips are always producing more hairs.
        
        Cortex
        
        Large storage area
        
        Outermost layers may show
        
        Hypodermis
        
        Prevent fungal/bacterial attacks
        
        Exodermis
        
        Bound by epidermis and endodermis
    - - Lycophytes
        
        Independent from euphyllophytes
        
        Selaginella sp example
        
        No root cap or root hairs.
      - Monocot group
        
        Lots of diversity
        
        Pith in center, endodermis surrounded by cortex.
        
        Monocot details, from inner to outer
        
        Pith in center
        
        Primary xylem next to pith
        
        Primary phlegm, smaller, around primary xylem
        
        Endoderm is a ring that surrounds the pith and xylem/phloem. Has casparian strip.
        
        Cortex surrounds endoderm and big vascular tissues.
        
        Epidermis on outside.
        
        Pericycle
      - Eudicot group
        
        Diversity
        
        NO PITH.
        
        Endodermis and cortex.
        
        Eudicot detail, formatted same as monocot details
        
        Primary xylem in center, sort of spiky appearance in cross section.
        
        Phloem around xylem, smaller cells
        
        Pericycle
        
        Endoderm, casparian strip inside it.
        
        Cortex surrounds endoderm and big vascular. Tissues
        
        Epidermis on outside.
- - - - Atmosphere 8-15x higher in CO2
      - ~4% O2
        
        Kept tissues thin as internal environment quickly becomes anoxic
        
        Very weak ozone
        
        High mutation rate!!!
        
        Mutagenic rays bad. Protection needed.
  - - - Many reasons but mainly due to structural/growing process similarities
      - "Plants are terrestrial algae?!?!?!"
    - - SPORES IN FOSSIL EVIDENCE.
        
        Mid-Ordovician 470 MYA
        
        Sporopollenin walls
        
        Cryptospores
        
        Probably liverworts???
        
        Liverwort macrofossils!!!!
        
        ~390 Mya!
        
        Middle Devonian
        
        Dichotomously branched
        
        Macrofossils in general
        
        First ones
        
        1 more item...
  - - - Vascularization came along later.
    - - Dominant sporophyte = no longer restricted to damp areas!