the stem

• Functions of the Stem

  • Supports leaves and reproductive structures
  • Conducts water, dissolved minerals, carbohydrates
  • Produces new living tissues
• Types of growth

  • Primary growth
  • Secondary growth
• Primary growth

  Lengthening of plant
• Primary growth

  • Herbaceous and present in both dicot and monocot
  • Monocots lack secondary growth
• Secondary growth

  Outward growth of plant
• Secondary growth

  • Woody and present in dicot
  • Present in most seed plants
• Growth differs from typical pattern (e.g., division and enlargement of parenchyma tissue)
• Tissues in Herbaceous Stems

  • Epidermis - protective outer layer
  • Vascular tissues - conducts dissolved materials
  • Storage tissues - cortex and pith
  • Ground tissues
• Epidermis

  Protective outer layer
• Vascular tissues

  • Xylem - water and dissolved materials
  • Phloem - dissolved carbohydrates (sucrose)
• Dicot vs Monocot Stem

  • Herbaceous dicot stems have vascular bundles arranged in a circle
  • Monocot stems have scattered vascular bundles
  • Has ground tissue instead of distinct cortex and pith
• Differences Between Stems and Roots

  • Stems have nodes and internodes, leaves, and buds
  • Roots have root caps and root hairs
• Node

  Area on stem where 1+ leaves are attached
• Internode

  Stem area between 2 successive nodes
• Bud


  Underdeveloped shoot that contains embryonic meristem
• Types of Buds

  • Terminal (tip of stem)
  • Axillary (side of stem)
• Internally in Herbaceous Roots

  • Possess endodermis and pericycle
• Stems lack pericycle and rarely have endodermis
• Wood

  • Secondary growth occurs in woody eudicots and conifers
  • Produced by vascular cambium between primary xylem and primary phloem
• Vascular Cambium


  • Lateral meristem that produces secondary xylem (wood) to inside and secondary phloem (inner bark) to outside
• Vascular cambium is not initially a solid cylinder of cells; it becomes continuous when production of secondary tissues begins
• Cork Cambium


  • Lateral meristem that produces cork parenchyma to inside and cork cells to outside
  • Makes up the outer bark of a woody plant
• Cork cambium arises near stem surface
• Cork Cambium Structure


  • Either continuous cylinder of dividing cells or overlapping arcs of meristematic cells that form from parenchyma cells in cortex and eventually secondary phloem
• Lenticels

  • Pores promote gas exchange of oxygen, carbon dioxide, and water vapour
• Annual Rings


  • Wood - Secondary xylem/interior side of vascular cambium
  • Bark - everything exterior of vascular cambium, including secondary phloem and periderm
• Secondary growth happens in roots too
• Stem Modifications

  • Rhizome
  • Tuber
  • Bulb
  • Corm
  • Stolon
  • Tendrils
  • Cladophyll
• Rhizome


  Horizontal underground stem that serves as storage organ and means of sexual reproduction
• Rhizome examples

  • Iris
  • Ginger
• Tuber

  Thickened end of rhizome that is fleshy and enlarged for food storage
• Tuber example

  • White potato
• Bulb


  Rounded, fleshy underground bud that consists of short stem with fleshy leaves
• Bulb example

  • Onion
• Corm


  Short, thickened underground stem specialized for food storage and asexual reproduction
• Corm example

  • Crocus
• Stolon


  Areal horizontal stem with long internodes; often forms buds that develop into separate plants
• Stolon example

  • Strawberry
• Tendrils


  Slender threadlike appendage of a climbing plant, often growing in spiral form, that stretches out and twines around suitable support
• Tendrils example

  • Grapes