1 Review What are three important functions of stems

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 plant

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

CH 23 PLANT STRUCTURE AND FUNCTION23.3 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

Nodes Where leaves are attached

Buds Contain apical meristems that

can produce new stems and leaves

Stems produce woody tissue in larger plants.

Monocot Stems

Clusters of xylem and phloem tissue are scattered throughout the stem

Ground tissue is fairly uniform consisting mainly of parenchyma cells.

Dicot Stems Vascular bundles are

arranged in a cylinder, or ring

Pith Parenchyma cells inside the

ring of vascular tissue Cortex

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 xylem

Heartwood Older xylem near the center of the stem no longer

conducts water.

Sapwood 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 light-colored 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

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.