stem

• Primary stem


  The herbaceous (non-woody) stem, which has not undergone secondary growth (the growth that produces bark and wood)
• Tissue types in primary stem

  • Epidermis
  • Ground tissue (cortex and pith)
  • Vascular tissue
• Epidermis


  The dermal tissue that surrounds and protects the stem, consisting of one layer of cells with a waxy cuticle
• Epidermis


  • Stomata allow for gas exchange
  • Trichomes help reduce transpiration, increase solar reflectance, and store compounds
• Ground tissue


  Fills much of the stem, forming the cortex and pith
• Cortex


  The outermost portion is collenchyma cells, the remainder is parenchyma cells
• Pith


  Consists of parenchyma cells
• Vascular tissue arrangements


  • Solenostele (continuous ring)
  • Eustele (distinct vascular bundles in a ring)
  • Atactostele (scattered vascular bundles)
• Formation of vascular tissue

  1. Procambium divides to produce primary xylem internally and primary phloem externally

  2. Fascicular cambium forms in some vascular bundles

  3. Primary phloem fibers (bundle caps/bundle sheath) produced outside primary phloem

  
• Leaf traces


  Strands of vascular tissue connecting leaves to the stem

  
• Leaf trace gaps


  Portions of stem without vascular tissue just above leaf traces
• Branch traces


  Strands of vascular tissue connecting axillary shoots to the main stem

  
• Branch trace gaps


  Portions of stem without vascular tissue just above branch traces