Download Stems

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
•
1)
2)
3)
4)
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 of Stems
• Herbaceous: softer
texture stems that die
at the end of the
growing season; nonwoody.
• Woody: hard textured
stems with secondary
xylem
• Woody stems longer
than 5m with a trunk
make the plant a tree.
Dicot Stems
• Pith in the center
• Outside of stem is still
the epidermis
• Lateral growth is due
to the vascular
bundles in a ring
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.
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)