Download Botany Ch6 Stems PPT

Chapter 6
Lecture Outline
Stems
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Outline

External Form of a Woody Twig

Origin and Development of Stems

Tissue Patterns in Stems
• Herbaceous Dicotyledonous Stems
• Monocotyledonous Stems
• Woody Dicotyledonous Stems

Wood and Its Uses

Specialized Stems
I. WOODY AND HERBACEOUS PLANTS
II. External Form of A Woody Twig-Gross Structure

Shoot System _________________________.

Woody Twig– gross structure.
• Node = ________________________________
- Arrangement of nodes—Arrangement of Leaves on Stem
- Alternate or spiral
- Opposite
- Whorled
• Internode = _____________________________
• Leaf = _________________________________.
• Axil - Angle between petiole
and stem
BUDS
• Bud scales:_______________
–
Function = ______________
• Bud Scale Scars: group of bud
scale scars for one year around
stem; indicates age
• Bud Contains: Apical Meristem,
Leaf Primordia, Bud Primordia
• Axillary Bud located in ______.
– Growth in __________________
• Terminal Bud
– Location: ___________________
– Growth in: ___________
• Stipules - Paired, often
leaflike appendages at
base of a leaf
• Deciduous: _________
–
Appearance of Twigs:
• Bundle scars mark food
and water conducting
tissue within leaf scars.
III. Origin and Development of Stems

Apical meristem at
stem tip
• Contributes to increase
in stem length
• Dormant before growing
season begins
• Protected by bud scales
and by leaf primordia
–
Leaf primordia - Tiny
embryonic leaves that
develop into mature leaves
Longitudinal section
through stem tip
Stems & Leaves in Embryonic Plants in a Seed

Cotyledons - Seed leaves attached to
embryonic stems
• Store food needed by young seedling
• Dicotyledons (Dicots) - Flowering plants that
_____________________
• Monocotyledons (Monocots) - Flowering plants
that _________________________________
IV. Tissue Patterns in Stems

HERBACEOUS PLANTS
Stele - Central cylinder of primary xylem,
primary phloem, and pith (if present)
Eusteles - Discrete vascular bundles
–
In flowering plants and conifers
Vascular Bundles
MATURE TISSUES– Microscopic View
Herbaceous Dicotyledonous
 Epidermis

Vascular Bundles =
• Tissues:
• Arrangement of bundles:

Secondary Growth: some

Cortex: Area ______________________

Pith: Area _____________________________
Dicot
Monocotyledonous

Monocots
• Epidermis
• No Secondary Growth
Cross section
of monocot
stem
• Vascular Bundles– location:
– Xylem closer to
center
–
Air Space
–
Fibers (sheath)
• No Pith or Cortex
–
Parenchyma
surrounds bundles.
Monocot vascular bundle
Woody Stems


Woody Plants: have lateral meristems
•
____________________
•
____________________
•
Secondary Growth =
Pattern of Tissue
• Bark
–
Periderm
o
–
Cork Cambium
2nd Phloem
• Vascular Cambium
• 2nd Xylem
• Pith
Woody Dicotyledonous Stems

Wood = Secondary xylem

Activity of Lateral Meristems
• Seasons: Annual Rings
–
–
–
Spring wood: secondary xylem w/ __________________
Summer wood: s”
“ _________
In conifers: have Tracheids
• No Seasons  Tropics:

Annual Ring =
–
Angiosperms: mostly vessel elements
–
Bulk of tree trunk consists of annual rings of wood.
• Age
• Climate

Vascular Cambium:

Phloem:
Cross section of young stem with
secondary growth

Vascular Ray: horizontal row of parenchyma
• Function:
• Xylem Ray -
• Phloem Ray -
Bark
Cross section of
young stem
with secondary
growth
Wood Categories

Heartwood: older, darker, in center
• Parenchyma cells accumulate
• Prevent conduction of
water
• Resin Canals
• Gums tannins

Sapwood: functional

Softwood

Hardwood
Resin canals
in pine
VI. Wood and Its Uses

50% of weight = water content.
• Dry part = 75% cellulose + 25% lignin.

Density - Weight per volume

Durability - withstand decay
• Tannins and oils

Knots - Bases of lost branches

Wood Products
• lumber
– Sawdust and waste = particle board and pulp.
– Veneer
• Pulp --Paper, synthetic fibers, plastics, linoleum
• Ifuel.
– 10% in US

Bark – Periderm and
Phloem
• Secondary Phloem =
Inner Bark
•
Laticifers - Ducts
have latex-secreting
cells
• Rubber, chicle
(chewing gum),
morphine

Periderm = Outer Bark
• Cork Cells
• Cork Cambium
• Other
• Function
Periderm
Bark
Cross section of young stem with secondary
growth
• Lenticels – made from Parenchyma cells
–
Function: _____________________
Gross View
Early Development
Mature Lenticel
V. Specialized Stems

Rhizomes - Horizontal stems just
below-ground
• Irises, some grasses, ferns

Runners - Horizontal stems
•
Make new plants at end
• Strawberry

Stolons - Produced beneath the
surface & give rise to tubers.
 Tubers– next slide

Tubers - Swollen, fleshy,
underground stem
• Store food
• Potatoes - Eyes = nodes for
making new plants

Bulbs - Large buds with
fleshy leaves & small stem
• Store food
• Make new plants
• Onions, lilies, hyacinths, tulips

Corms – mostly stem
tissue, with papery
leaves
• Store food
• Make new plants
• Crocus & gladiolus

Cladophylls Flattened, leaf-life
stems
• Photosynthesis
• Store water
• prickly pear cactus
Prickly pear cactus
Review

External Form of a Woody Twig

Origin and Development of Stems

Tissue Patterns in Stems
• Herbaceous Dicotyledonous Stems
• Woody Dicotyledonous Stems
• Monocotyledonous Stems

Specialized Stems

Wood and Its Uses
Life Span of Plant

Annuals - Plants that die after going from
seed to maturity within one growing season
• Type of Plant:
• Monocot or Dicot:
• Primary or Secondary:

Bienial

Perrennial