1. Stems and Plant Growth Basics

2. Shoots vs. Roots Stems are part of the shoot system (stems, leaves, flowers) The shoot system depends on the roots for water and minerals, and to store excess sugar created by photosynthesis

3. Anatomy of a Stem Node: area where leaf branches off from stem Internode: area in between nodes Apical meristem: terminal bud where upward growth in concentrated Axillary bud: site of new branches Petiole: area connected leaf to stem

4. Anatomy of a Stem Leaf scar: area where leaf has fallen from stem Terminal bud scar: remnant of previous year’s terminal bud; marks one year of growth

5. Terminal vs. Axillary Buds The growth of young shoots is concentrated at the terminal bud, where cells are dividing rapidly The terminal bud is dominant over the axillary buds in young plants, keeping them dormant We can prune/pinch plants to influence shape – Trimming terminal bud increases width – Trimming axillary buds increases height

6. Inside a Stem Young stems are made of xylem, phloem, a pith, vascular cambium, and epidermis – Xylem: transports water from roots to leaves – Phloem: transports sugar from leaves to roots – Pith: center of stem; functions in storage – Vascular cambium: layer of cells that makes new xylem and phloem – Epidermis: protective coating

7. Inside a Stem Dicots have a large central pith, with vascular bundles around the edges (a vascular cylinder) Monocots have vascular bundles randomly dispersed throughout the pith

8. Why do plants grow forever? Plants can grow throughout their lives because of meristems Meristems are bundles of stem cells that make new cells throughout a plant’s life – Apical meristems: responsible for primary plant growth (increase in height) – Lateral meristems: responsible for secondary plant growth (increase in diameter)

9. Primary Plant Growth Apical meristems are located at the tips of roots and stems Apical meristems give rise to the epidermis, vascular tissue (transport), and ground tissue (storage)

10. Secondary Plant Growth Secondary growth increases plant diameter Lateral meristems cause secondary growth – Vascular cambium – Cork cambium

11. Vascular Cambium The vascular cambium is located between layers of xylem and phloem The vascular cambium makes secondary xylem and phloem (wood and bark)

12. Cork Cambium The cork cambium makes cork, a tough outer coating that replaces the epidermis on stems and roots This is what we think of as ‘bark’, but technically bark includes secondary phloem, the cork cambium, and cork