Plant Groups and Stem/Root Growth

Plant Groups (Based on Lifespan and Flowering Time)

• Annuals: Plants that complete their life cycle (grow to maturity, flower, produce seeds, and die) in a single growing season.
• Biennials: Plants that live for two years.
• Perennials: Plants that live for more than two years.

Herbaceous Plants

• Plants whose stems have little or no woody tissue.

Stem Growth

• Location of Lengthwise Growth: Stems grow in length at the tips due to cell division in the apical meristem.
• Zone of Elongation: Newly formed growth cells grow larger in the zone of elongation, located behind the meristem.
• Zone of Maturation: Cells differentiate into the various cells that make up the stem in the zone of maturation.

Dicot Stem Thickness Growth

• Dicot stems grow thicker through growth in the vascular and cork cambium.
• Xylem tissue adds more thickness than phloem tissue.

Vascular Tissue Layers

• New Layers: Secondary xylem and secondary phloem.
  • Xylem tissue faces the center of the stem.
  • Phloem tissue faces the outside of the stem.

Sapwood, Heartwood, and Annual Rings

• Sapwood: Water-conducting tissue.
• Heartwood: Xylem tissue that no longer conducts water but provides strength and support to the stem.
• Annual Rings:
  • Made up of large xylem cells (lighter color) formed during the spring.
  • Smaller xylem cells (darker color) formed during the summer and fall.
  • New and old xylem cells become the wood of the tree.

Monocot Stems

• Most monocot stems do not grow thicker because they lack vascular cambium tissue.

Root Growth

• Location of Lengthwise Growth: Roots grow in the apical meristem at the tip of the root.
• Protection of New Cells: New cells are covered by a tough root cap that lubricates and protects them as they push into the soil.