The Shoot

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The Shoot

• Chapter 26

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Shoot Morphology

• Stems and leaves
• Terminal and axillary buds
• Bud scales
• Nodes and internodes
• Leaves have
• Petioles, blades, stipules
• Leaf gaps and traces

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Croton Shoot Main functions of stem are support
and conduction
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Origin and development of stems

• Dormant buds
• Apical meristem divides periclinally and
  anticlinally
• Leaf primordia leaves
• Bud primordia-branches
• Shoot apex has tunica-corpus organization

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Tunica-corpus organization
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Primary structure of stem

• Protoderm develops into Epidermis (1-cell
  thick)with cuticle
• Procambium develops into xylem and
  phloem-vascular bundles
• Ground meristem develops into parenchyma, pith
  (hollow cells in center) and cortex around the
  pith

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Monocot anatomy without secondary growth
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Stem structure continued

• Vascular cambium develops between primary xylem
  and phloem, develops secondary xylem and phloem
• Strands of vascular tissue break off and enter
  leaf. Called leaf traces
• Woody plants develop cork cambium, produces cork
  cells and lenticels

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Basic types of stem organization

• Stele-central cylinder of primary xylem, phloem,
  and pith
• Continuous cylinder (conifers, magnoliids,
  eudicots)
• Discrete bundles in a ring
• Bundles scattered throughout ground tissue
  (monocots)

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Transverse section of basswood
(Tilia) Continuous cylinder type
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Transverse section of Elderberry
(Sambucus) Discrete bundles in a ring type
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Closed Vascular Bundle of buttercup
(Ranunculus), a herbaceous eudicot with discrete
bundles but little secondary growth
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Maize stem-Scattered vascular bundles throughout
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Differentiation of vascular bundles in Maize
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Branch traces and leaf traces
Gaps are regions lacking ground tissue Traces are
extensions of vascular tissue to the leaf
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Specialized stems

• Rhizomes-horizontal stems below ground
• Stolons and runners-horizontal stems above ground
  (stawberries)
• Both rhizomes, stolons, and runners can produce
  adventitious roots
• Tubers-Stems modified for storage (potato)
• Tubers have buds (green eyes of potato)

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Specialized stems continued

• Bulbs-large buds with small stem surrounded by
  fleshy leaves below (onion, tulip)
• Corms resemble bulbs-mostly stems with a few
  papery leaves (Gladiolus, crocus)
• Cladophylls-leaf like stems (Cactus)
• Tendrils-modified stems for climbing plants

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Leaves

• Primary function is photosynthesis
• Convert sunlight energy to stored chemical energy
• Exchange gases with atmosphere
• CO2 enters
• O2 exits
• H20 exits as water vapor

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Leaf Morphology

• Leaf size-1mm to 6m wide
• Shapes vary tremendously
• Deciduous or evergreen
• Simple or compound (many leaflets)
• Compound can be paripinnate, imparipinnate,
  palmate, trifoliate, bipinnate
• Phyllotaxy (arrangement of leaves on stems)
• Alternate, distichous, opposite, whorled,
  decussate
• Venation-Parallel or Netted (reticulate)

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Leaf Morphology
Pinnately compound Leaf above
Sessile, simple leaves above
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Leaf Anatomy

• Epidermis-Outer surface of leaf
• 1-cell layer thick, waxy cuticle, has stomata,
  trichomes (hairs, glands)
• Mesophyll-Tissue below epidermis
• Photosynthesis, palisade layer (stacked
  parenchyma) and spongy mesophyll layer (air
  pockets) together chlorenchyma tissue
• Veins (vascular bundles) xylem and phloem,
  surrounded by bundle sheaths

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Transverse sections of lilac leaf
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Paradermal section of lilac
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Lower epidermis of lilac
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Leaf Anatomy-Transverse Section of Water Lily
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Stomata at right
Recessed stomata at right (crypts)
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Leaf development in Coleus
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Abscission layer in leaves
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Specialized leaves

• Sun and shade leaves
• Arid region leaves
• Aquatic plants
• Tendrils
• Spines, thorns, and prickles
• Storage leaves
• Flower pot leaves
• Reproductive leaves

• Floral leaves
• Insect-trapping leaves
• Pitcher plants
• Sundews
• Venus flytraps
• bladderworts

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Water-storing Epidermis of Peperomia leaves
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Human use of stems and leaves

• Biggest use of stems is for wood
• Leaves
• Horticulture (color, deciduousness)
• Cooling effects of shade in cities
• Food-spinach, cabbage, parsley, lettuce, chard,
  celery and rhubarb (petioles)
• Spices-thyme, marjorem, oregano, taragon, bay,
  leaf, basil, spearmint, wintergreen, dill,
  cilantro, peppermint

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Human use of leaves

• Dyes and fibers-agave, palm leaves
• Resins and oils-pennyroyal, camphor, eucalyptus,
  patchouli
• Thatching for roofs Palm trees
• Drugs-tabacco, tea, tequila, mezcal, cocaine,
  belladona, digitalis
• Insecticides and waxes-Neem tree and Carnuba palm