1. Plant Stems -Part 3
Stems

2. Stem
Main function: to hold up the leaves and conduct substances between the root and the leaves.
Two types of stems: herbaceous and woody.
Herbaceous stems are green and soft, they do not survive through winters and must regrow each year. Vascular bundles with the xylem and phloem.
Xylem is closer to the centre, phloem is closer to the outside of the stem.
Vascular bundles of the herbaceous monocot are found throughout the stem.
Vascular bundles of the herbaceous dicot are arranged in a ring closer to the outside. They also have a vascular cambium between the xylem and phloem.

3. Monocot stem dicot stem

4. Woody stems are more complex, are tough and hard, commonly called wood, and can survive through the winter.
Grow thicker over time due to the vascular cambium making new xylem and phloem.
Sapwood is younger xylem, conducts the water and minerals. The older xylem fills with resins, oils and other chemicals and is called heartwood.
The growth of new xylem each spring results in a new layer of sapwood and an annual ring is formed.
Outer part is called the bark.
Protects the tissue
Contains cork tissue
Outer cork cells are dead and contain fats, oils, waxes

6. Stems can also store food Modified stems:
Rhizomes are thick, fleshy stems that grow on or just below the soil’s surface.
Tubers are stems that grow underground. They have a lot of stored food in them and have eyes that grow into buds.
Bulbs are underground stems: surrounded by modified leaves

7. Human Uses of Stems Fuel: ethanol, wood
Food: sugar cane, potatoes, maple syrup, asparagus
Textiles: flax, hemp, bamboo
Dyes: indigo
Other chemicals: tannin (wood stain), turpentine, latex rubber
Medicine: salicyclic acid (pain reliever from willow bark), taxol (anti-cancer drug made of yew tree bark)