Stems

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.

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.

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

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

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

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

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

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.

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.

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.

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 - http://uregina.ca/~sauchyn/geog411/dendrochronology.html

Christmas Tree – 17 years old – cut down Dec 2009 2002-2004 had more average warmth and rain during the summers – growth averaged15%/year Above average warm and wet summers produce optimal growing seasons such as 2005-2007 – 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

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)

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

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)