1. Stems

2. Stems 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.

3. Stems
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.

4. Stem functions Stems have four main functions:
Support and elevation for leaves, flowers and fruits
Transport of materials between the roots and the shoots
Nutrient Storage
Annual, lateral, plant growth

5. Types Woody Stems Herbaceous Stems Contain thick, tough tissue (wood)
Found in plants that live for more than a year
Trees and shrubs
Herbaceous Stems
Contain soft, green, juicy tissues
Found in plants that live for one year

6. Monocot Stems (note – no vascular cambium)
Herbaceous Stems
Vascular bundles scattered throughout the stem
ie. Corn
Woody Stems
Vascular bundles are scattered throughout the stem
ie. palm tree
Note Stem diameter will not change with time

7. Dicot Stems Herbaceous Stems Woody Stems
Vascular bundles arranged in ring in cortex
Vascular bundles consist of out phloem and inner xylem
In between the xylem and phloem is vascular cambium
ie. Beans
Woody Stems
Annual rings are present
Result of new xylem produced each growing season
Ie. Maple tree

8. Parts (diagram is of woody dicot)
Pith – storage
Vascular cambium
contains plants lateral meristems
produces xylem and phloem
resp for increasing width
Cork Cambium – produces tissues of periderm
Periderm/Cork
Region outside cork cambium
Epidermis
produced from cork cambium
protection from environment (parasites, animals and disease)
Additional Terms:
Wood - xylem from vascular cambium
Bark – all parts outside vascular cambium

9. Dicot Stems IF 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.

10. Dicot Stems
The 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.

11. Monocot 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.

12. Dendrochronology
Dendrochronology, the study of the annual growth in trees, is the only method of paleoenvironmental research that produces proxy data of consistently annual resolution. 
Trees add a cone of wood each year.  Initially the cells are thin walled to conduct the abundant spring soil moisture. As soil water declines through the summer, the cells become thicker-walled and more dense.
Each annual ring consists of early (light) and late (dark) wood. 
Source: University of Regina -

13. Christmas Tree – 17 years old – cut down Dec 2009
had more average warmth and rain during the summers – growth averaged15%/year
Above average warm and wet summers produce optimal growing seasons such as – growth averaged17.3% /year
2009 had a cool and wet summer, 2008 had a dry and warm summer – growth averaged 9.5%/year
1992-
2001
2002-
2004
2005-
2007
2008-
2009
2009
2008
2007
2006
2005
2004
2003
2002
Tree taken from West Carleton ~ 5 km from Stittsville

14. Specialized 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)

15. Specialized Stems
Corm: short, enlarged, underground stem (gladiolus, crocus)
Rhizome: a horizontal, underground stem used mainly in reproduction, but also in storage (ferns, iris)

16. Specialized 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)