1 Review What are three important functions of
Explain How does the arrangement of vascular
bundles in monocot stems differ from dicot stems
Apply Concepts How do the functions of a stem
relate to the functions of the roots and leaves of a
2 Review Define primary and secondary growth
Predict Describe what would happen over time to a
tree sapling that could grow only taller, not wider
23.3 Stems
Stem Functions
Stems produce leaves, branches, and flowers
Stems hold leaves up to the sun
Stems transport substances throughout the plant.
Anatomy of a Stem
Epidermal cells have thick cell walls and a waxy
protective coating.
Anatomy of a Stem
 Where
leaves are attached
 Contain
apical meristems that
can produce new stems and
Stems produce woody tissue
in larger plants.
Monocot Stems
Clusters of xylem and
phloem tissue are
scattered throughout the
Ground tissue is fairly
uniform consisting mainly
of parenchyma cells.
Dicot Stems
Vascular bundles are
arranged in a cylinder, or
 Parenchyma
cells inside the
ring of vascular tissue
 Parenchyma
cells outside
the ring of vascular tissue.
Primary Growth
Growth that occurs at the apical meristems.
Secondary Growth
Stems increase in thickness to support larger plant.
Secondary Growth
Very common among dicots and non-flowering
seed plants such as pines
Rare in monocots
Dicots have meristems within stems and roots that
produce true secondary growth
Dicots can grow much larger.
Conifers and Dicots
Secondary growth takes place in meristems called:
Vascular cambium
 Produces
vascular tissues and increases the thickness
of stems over time
Cork cambium
 Produces
the outer covering of stems.
Vascular cambium appears as a thin, cylindrical
layer of cells between the xylem and phloem of
each vascular bundle.
Divisions in the vascular cambium give rise to new
layers of xylem and phloem
Cambium continues to produce new layers of
vascular tissue each year, causing the stem to
become thicker.
Formation of Wood
Most of “wood” is actually layers of secondary
 Older
xylem near the center of the stem no longer
conducts water.
 Active
in fluid transport and is usually lighter in color.
Tree Rings
Spring growth
 Vascular
cambium begins to grow rapidly, producing
large, light-colored xylem cells, resulting in a lightcolored layer of early wood
As growing season continues
 Cells
grow less and have thicker cell walls, resulting in
a layer of darker wood
Thick rings good growing conditions and thing rings
poor growing conditions.
Formation of Bark
 All
tissues found outside the vascular cambium
 Tissues include phloem, the cork cambium, and cork.
Cork cambium produces a thick, protective layer of
waterproof cork that prevents water loss.
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