Secondary Growth in Stems

Overview of Primary and Secondary Growth
Primary growth – common to ALL vascular plants
• Extends the length of a plant both aboveground and belowground
• Originates in root apical meristems (RAM) and shoot apical meristems (SAM)

Secondary growth – occurs in woody plants
• Thickening growth
• Occurs from lateral, (NOT apical) meristems, found inside the stem (and the root)
• Monocots don’t have secondary growth

Annuals, Biennials, and Perennials
Annuals
The entire growth cycle (seed germination  vegetative plant  flowering plant  seed formation) occurs within a single growing season, then the plants die
Examples: wildflowers, weeds, garden flowers, most vegetables and
grains

Biennials
Plants that take two years (seasons) to complete their life cycles
First season: formation of root, short stem, a rosette of leaves

In order to flower, they require a cold treatment (vernalization) before
they can flower
Second season: plants flower, develop fruits, seeds, and die
Examples: parsley, members of the onion and cabbage family, carrot

Perennials
Their vegetative structures live year after year
Examples: herbaceous perennials (have dormant rhizomes, bulbs,
tubers, roots) and woody perennials (vines, shrubs, trees)