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Root vs Stem Development

Roots RAM protected by root cap Roots lack nodes Lateral roots develop deep within root Structural support is less important Endodermis Water absorbing root hairs Cuticle is very thin—if present. Root vs Stem Development. Roots RAM protected by root cap Roots lack nodes

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Root vs Stem Development

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  1. Roots RAM protected by root cap Roots lack nodes Lateral roots develop deep within root Structural support is less important Endodermis Water absorbing root hairs Cuticle is very thin—if present Root vs Stem Development

  2. Roots RAM protected by root cap Roots lack nodes Lateral roots develop deep within root Structural support is less important Endodermis Water absorbing root hairs Cuticle is very thin—if present Root vs Stem Development

  3. Roots RAM protected by root cap Roots lack nodes Lateral roots develop deep within root Structural support is less important Endodermis Water absorbing root hairs Cuticle is very thin—if present Stems SAM protected by leaf primordia Stems have nodes Leaves & branches develop from surface layer at axillary/lateral bud Structural support is very important No endodermis Cuticle present to prevent dessication Ventilation Root vs Stem Development

  4. What are functions of a stem? • Photosynthesis • Produce leaves • Provide support • Transport food • Transport water • Protection • Elevate leaves

  5. Stems & Leaves • Apical meristem produces more stem, leaves, and flowers • Photosynthesis considerations • Ventilation • Maximize light absorption • Transport photosynthesis products & water • Development of lateral branches • Allow for secondary growth • Develop a new meristem • (topic next week)

  6. Terminal Buds of Wood Plant Contain Shoot Apical Meristem • Scales are modified leaves that protect SAM and leaf primordia from winter, dryness.

  7. Dicot Flowering PlantsAdditions Carrots, fennel, anise, parsley, celery Beans, peas, clover, alfalfa Peppermint, catnip, oregano, thyme, lavender Maples

  8. Sunflower Stem Cross Section “Dicot” Vascular bundles in a ring Pith Distinct collenchyma

  9. Epidermis Collenchyma Cortex Phloem Xylem Pith—parenchyma cells

  10. Epidermis Collenchyma Cortex Phloem Xylem Pith—parenchyma cells

  11. Collenchyma provides support in elongating stem—thickened primary cell walls How do we determine if this is a primary or secondary cell wall?

  12. Formation of primary xylem with some secondary cell walls —cells are elongating as secondary cell walls are produced

  13. Collenchyma—living cells of outer cortex with angular thickening in 1°CW Primary Xylem Water transport & support Inside of phloem Vessel elements, fibers, tracheids, parenchyma Primary Phloem Sucrose & some plant hormone transport Companion cells & Sieve tube members Epidermis Trichomes—protection Reduce water loss Cuticle Waxy layer Reduce water loss Antimicrobial properties Cortex—parenchyma cells Storage Photosynthetic Air spaces Pith—parenchyma storage Primary Stem Tissues

  14. Modified Stems Thorns Honey Locust-Gleditsia Hawthorn-Crataegus

  15. Modified Stems Tendrils Grape-Vitis Cucumber--Cucumis

  16. Monocot Stems have Vascular Bundles that are Scattered Next Slide

  17. New Monocots that are Important Banana, Ginger, Palm, Rice, Wheat, Onion & Garlic

  18. Tulip Pineapple Banana Ginger Orchid Iris

  19. Stem Adaptations to Xeric Environments http://www.usparksonline.com/arizona-national-parks.htm

  20. The Cactus-Like Stem Design“succulents” • Large volume to surface area • Minimize exposure & evaporation • Columnar Shape • Avoid direct sunlight during heat of midday

  21. The Cactus-Like Stem Design“Succulents” • Large volume to surface area • Minimize exposure & evaporation • Columnar Shape • Avoid direct sunlight during heat of midday • Accordion folds • Allow for stem expansion when water is plentiful • Leafless • Reduce surface area and water loss

  22. Desert Lily Liliaceae Desert Milkweed Apocynaceae Desert Grape Vitaceae Desert Poinsettia Euphorbiaceae A True Cactus Cactaceae

  23. Convergent Evolution *unrelated organisms evolve a similar strategy in response to a common selective pressure Desert Lily Liliaceae Desert Milkweed Apocynaceae Desert Milkweed Desert Grape Vitaceae Desert Poinsettia Euphorbiaceae A True Cactus Cactaceae

  24. Cacti have spines in clusters called areoles Spines inflict pain and are difficult to remove.

  25. Cacti just don’t belong everywhere.

  26. Stem Review • Shoot apical meristem • Function • Compare with RAM • Tissues of primary stems • Structure & function • Monocot versus Dicot • Convergence evolution of desert Succulents

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