Stems

What is a stem?

  • A stem is an organ that performs the function of transporting water/minerals to areas of photosynthesis, as well as supporting leaves and smaller stems.

  • Buds are located along the stem to allow for the creation of new shoots and branching. Buds are not found in roots or leaves.

  • Stems tend to be cylindrical in shape, therefore round in cross-section, although some stems can be square (e.g. mints) or triangular (e.g. sedges) in cross-section

    • N.B. some photosynthetic stems can be two-dimensional and leaf-like called cladophylls. These stems would still have axillary buds, not found in leaves, and the anatomy of leaves and stems would differ.

  • Stems are some of the most ancestral organs found in land plants, especially rhizomes that creep along the soil, also creating upright stems that grow toward the sun

    • N.B. rhizomes appear to be quite root-like but these stems would still have axillary buds, not found in roots, and the anatomy of roots and rhizomes would differ.

  • Some ancestral plants, such as mosses, have stems that lack vascular tissue, but these stems can still move water and support leaves.

What are the functions of stems?

Stems of most plants perform two functions: transport and support

Transport

  • Vascular tissues move water from roots through plant body to areas of photosynthesis. Stems also move sugars created in photosynthesis to areas of active growth

Support

  • Stems provide structure for the plant, allowing leaves to reach the sun, and flowers and fruits to reach necessary heights.

Subtopics

Germination

Stem Structure

Primary Growth

Monocots vs. Eudicots

Lateral Stem Development

  • Lateral stems, or shoots, grow from axillary buds (latent apical meristems)

  • Buds create new shoot systems

Secondary Growth

Specialized Stems

Laboratory

  1. Monocot stem (x.s.)

    • LABEL: Epidermis, Vascular Bundle (Xylem, Phloem, Sclerenchyma)

  2. Dicot stem (x.s.)

    • LABEL: Epidermis, Cortex, Pith, Vascular cylinder (Xylem, Phloem, Sclerenchyma, Cambium)

  3. Tilia (basswood) 3-year-old stem (x.s.)

    • LABEL: Pith, Primary xylem, Secondary xylem (wood), Vascular cambium, Secondary phloem, Cork cambium, Periderm

Above: Cross-section of Basswood (Tilia); 3-year stem (x40)

Above: Cross-section of a monocot stem (x40)

Above: Cross-section of a dicot stem (x40)

Questions for Thought

  • How are stems structurally different from roots?

  • What is a hypocotyl? an epicotyl?

  • How is "primary growth" defined?

  • How do young stems develop?

  • What is the difference between determinate and indeterminate growth?

  • What are the external features of a young stem?

  • What is the function of axillary buds?

  • How does internal stem structure differ in monocots and eudicots?

  • What is secondary growth, and how does it function?

  • What is a growth ring, and how is related to the vascular cambium?

  • What is a stem adaptation to an arid environment?

  • What is the difference between a stem tendril and leaf tendril?

  • What is the same/different between a corm, a rhizome, a stolon, and a tuber?

  • What are some ways in which plants use specialized roots and/or specialized stems to increase their spread in the environment?

  • See also the leaf section for comparison questions