Chapter 6 Lecture Outline Stems Copyright The Mc

Chapter 6 Lecture Outline Stems Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Outline v External Form of a Woody Twig v Origin and Development of Stems v Tissue Patterns in Stems • Herbaceous Dicotyledonous Stems • Monocotyledonous Stems • Woody Dicotyledonous Stems v Wood and Its Uses v Specialized Stems

I. WOODY AND HERBACEOUS PLANTS II. External Form of A Woody Twig-Gross Structure v Shoot System _____________. v 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 v 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 v 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 v 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 v Epidermis v Vascular Bundles = • Tissues: • Arrangement of bundles: v Secondary Growth: some v Cortex: Area ___________ v Pith: Area _______________ Dicot

Monocotyledonous v 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 v v Woody Plants: have lateral meristems • ____________________ • Secondary Growth = Pattern of Tissue • Bark – Periderm o – Cork Cambium 2 nd Phloem • Vascular Cambium • 2 nd Xylem • Pith

Woody Dicotyledonous Stems v Wood = Secondary xylem v Activity of Lateral Meristems • Seasons: Annual Rings – – – Spring wood: secondary xylem w/ _________ Summer wood: s” “ _____ In conifers: have Tracheids • No Seasons Tropics:

v Annual Ring = – Angiosperms: mostly vessel elements – Bulk of tree trunk consists of annual rings of wood. • Age • Climate v Vascular Cambium: v Phloem: Cross section of young stem with secondary growth v Vascular Ray: horizontal row of parenchyma • Function: • Xylem Ray • Phloem Ray -

Bark Cross section of young stem with secondary growth

Wood Categories v Heartwood: older, darker, in center • Parenchyma cells accumulate • Prevent conduction of water • Resin Canals • Gums tannins v Sapwood: functional v Softwood v Hardwood Resin canals in pine

VI. Wood and Its Uses v 50% of weight = water content. • Dry part = 75% cellulose + 25% lignin. v Density - Weight per volume v Durability - withstand decay • Tannins and oils

v Knots - Bases of lost branches v Wood Products • lumber – Sawdust and waste = particle board and pulp. – Veneer • Pulp --Paper, synthetic fibers, plastics, linoleum • Ifuel. – 10% in US

v Bark – Periderm and Phloem • Secondary Phloem = Inner Bark • Laticifers - Ducts have latex-secreting cells • Rubber, chicle (chewing gum), morphine

v 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 v Rhizomes - Horizontal stems just below-ground • Irises, some grasses, ferns v Runners - Horizontal stems • Make new plants at end • Strawberry v Stolons - Produced beneath the surface & give rise to tubers. v Tubers– next slide

v Tubers - Swollen, fleshy, underground stem • Store food • Potatoes - Eyes = nodes for making new plants v Bulbs - Large buds with fleshy leaves & small stem • Store food • Make new plants • Onions, lilies, hyacinths, tulips

v Corms – mostly stem tissue, with papery leaves • Store food • Make new plants • Crocus & gladiolus v Cladophylls Flattened, leaf-life stems • Photosynthesis • Store water • prickly pear cactus Prickly pear cactus

Review v External Form of a Woody Twig v Origin and Development of Stems v Tissue Patterns in Stems • Herbaceous Dicotyledonous Stems • Woody Dicotyledonous Stems • Monocotyledonous Stems v Specialized Stems v Wood and Its Uses

Life Span of Plant v Annuals - Plants that die after going from seed to maturity within one growing season • Type of Plant: • Monocot or Dicot: • Primary or Secondary: v Bienial v Perrennial