Plant Growth


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Primary and Secondary G

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Plant Growth

  2. 2. Meristems generate cells for new organs Primary growth in stemsShoot apicalmeristems Epidermis(in buds) Cortex Primary phloem Primary xylem Vascular cambium Lateral Pith Cork meristems cambium Secondary growth in stems Periderm Cork Pith cambium Cortex Primary Primary xylem phloem Root apical Secondary meristems xylem Secondary phloem Vascular cambium
  3. 3. Woody plants Terminal bud Bud scale•In woody Axillary budsplants, primary Leaf scar This year’s growth Nodeand secondary (one year old) Stemgrowth occur Internodesimultaneously One-year-old side branch formedbut in different from axillary bud near shoot apexlocations Last year’s growth Leaf scar (two years old) Scars left by terminal bud scales of previous winters Growth of two Leaf scar years ago (three years old)
  4. 4. Primary Growth of Roots Cortex Vascular cylinder EpidermisKey Zone of Root hair maturation Dermal Ground Vascular Zone of elongation Apical Zone of cell meristem division Root cap 100 µm
  5. 5. Primary Growth of Shoots Apical meristem Leaf primordia•A shootapicalmeristemgives rise to arepetition of Developing vascularinternodes strandand leaf-bearing nodes Axillary bud meristems 0.25 mm
  6. 6. How a plant grows from a seed – primary growth •
  7. 7. Secondary growth adds girth to stems and roots in woody plants•Occurs in stems Primary and secondary growth in a two-year-old stemand roots of Epidermiswoody plants Cortex Primary phloem Pith Primary xylem Vascular cambiumbut rarely in Vascular cambium Primary Primary phloem Cortex Epidermis xylem Phloem rayleaves Pith Xylem ray•Produced by Primary xylemthe vascular Secondary xylem Vascular cambium Secondary phloem Primary phloemcambium and Periderm First cork cambium Corkcork cambium (mainly cork cambia and cork) Primary phloem Secondary phloem Secondary Vascular xylem (two cambium years of Secondary production) xylem Vascular cambium Secondary phloem Bark Primary xylem Most recent Pith cork cambium Layers of Cork periderm
  8. 8. Secondary growth adds girth to stems and roots in woody plants Secondary phloem Vascular cambium Late wood CorkSecondary cambium Peridermxylem Early wood Cork Transverse section of a three-year- old Tilia (linden) Xylem ray stem (LM) Bark 0.5 mm 0.5 mm
  9. 9. Secondary xylem•As a tree Growth ringages, theolder layers Vascularof raysecondaryxylem no Heartwood Secondarylonger xylem Sapwoodtransportwater and Vascular cambiumminerals Secondary phloem Bark Layers of periderm