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

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 stem

Monocotyledonous  Monocots Epidermis No Secondary Growth Vascular Bundles– location: – Xylem closer to center – Air Space – Fibers (sheath) No Pith or Cortex – Parenchyma surrounds bundles. Cross section of monocot stem Monocot vascular bundle

Woody Stems  Woody Plants: have lateral meristems ____________________ Secondary Growth =  Pattern of Tissue Bark – Periderm o Cork Cambium – 2 nd Phloem Vascular Cambium 2 nd Xylem Pith Cross section of young stem with secondary growth

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:  Vascular Ray: horizontal row of parenchyma Function: Xylem Ray - Phloem Ray - Cross section of young stem with secondary growth

Bark

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 Cross section of young stem with secondary growth Periderm Bark

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