Stems. Stems A stem is the other structural axis for the plant after roots. It is composed of nodes...

StemsStems

StemsStems

• A stem is the other structural axis for the plant after roots.

• It is composed of nodes and internodes.

• Nodes hold buds which can grow into leaves, flowers, cones, branches, etc…

• Internodes are the spaces between nodes.

StemsStems

• A shoot is not the same as a stem! Shoots are any new plant growth, not just new stems.

• Stems are usually located above the surface, but there are some plants with underground stems.

Stem functionsStem functions

• Stems have four main functions:

1) Support and elevation for leaves, flowers and fruits

2) Transport of materials between the roots and the shoots

3) Nutrient Storage

4) Annual, lateral, plant growth

Types of StemsTypes of Stems

• Herbaceous: softer texture stems that die at the end of the growing season; non-woody.

• Woody: hard textured stems with secondary xylem

• Woody stems longer than 5m with a trunk make the plant a tree.

Dicot StemsDicot Stems

• Pith in the center• Outside of stem is still

the epidermis• Lateral growth is due

to the vascular bundles in a ring

Dicot StemsDicot StemsIF WOODY STEM:

• Each vascular bundle has a meristem between the xylem and phloem

• Secondary xylem grows to the inside, while secondary phloem grows to the outside

• The epidermis and cortex get destroyed as the secondary xylem and phloem grow.

Dicot StemsDicot StemsThe plant produces a cork

cambium layer on the outside which replaces the epidermis.

• The outer region develops into the bark which protects the outside of the woody dicot.

• Secondary Xylem is known as heartwood, while secondary phloem is known as sapwood.

Monocot StemsMonocot Stems

• Have vascular bundles throughout, though usually concentrated near the edge.

• Rarely produce secondary growth as they are rarely woody.

• Grow laterally due to anomalous growth.

Specialized StemsSpecialized Stems

• Bulb: short underground stem with fleshy leaves attached (tulip, onion, daffodil)

• Climbing: stems that cling to or wrap around other plants or structures (ivies, vines)

Specialized StemsSpecialized Stems

• Corm: short, enlarged, underground stem (gladiolus, crocus)

• Rhizome: a horizontal, underground stem used mainly in reproduction, but also in storage (ferns, iris)

Specialized StemsSpecialized Stems

• Stolons/Runners: horizontal, above ground stems to produce new rooted plantlets when they touch the surface (strawberries, spider plants)

• Tuber: swollen, underground stems used for storage (potatoes)