Leaf form and function

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Leaf - form and function

• Leaves can differ greatly in shape, margin,
  venation and attachment
• Often the first thing looked at for
  identification
• Have blade, petiole and usually a stipule

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Leaf structure
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Leaf form

• Simple leaves have one blade
• Veins may be
• netted (dicot)
• parallel (monocot)

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• Examples of pinnately netted venation
• palmately netted venation

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Axillary buds

• Axil of leaf (the angle between the stem and
  the petiole)

Bud
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Leaf arrangement

• Leaflets are found on compound leaves
• Buds in the axil of the leaf
• Pinnately compound leaves
• leaflets opposite (odd or even )
• Palmately compound
• leaflets arise from same point

Palmate
Even
Bud
Odd
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• Three patterns of leaf attachment

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Leaf anatomy

• Cuticle
• Upper epidermis
• Palisade parenchyma
• Vascular bundle
• Spongy parenchyma
• Lower epidermis
• Stoma

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Leaf x-section (photomicrograph)

• Note stomatal chamber
• Palisade parenchyma may be one or several layers

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Leaf x-section

• Note the stomatal chamber

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Stomata (leaf pores)

• Ivy lower epidermis
• Stomata with guard cells

Corn epidermal peel
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Stoma with chamber

• An open area or chamber is found below (to the
  inside of) the stomatal opening

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Diffusion

• Materials diffuse from areas of highest to lowest
  concentration
• It is a random process

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Pore diffusion

• Many small pores are more efficient at diffusion
  than one large pore of the same total area.
• Diffusion is more linked to circumference than to
  area

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Pore diffusion

• Spill over accounts for the perimeter effect

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Leaf pores - stomata

• Guard cells can expand and open a pore between
  them
• Opening affected by light, CO2, hormones,
  dehydration, biological clock

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Guard cell mechanism

• Closed condition
• Inner walls meet

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Guard cell mechanism

• Movement of K into the cells causes water
  movement into the cell, expanding it.

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Leaf abscission

• Abscission zone near base of petiole

Bud
Petiole
Stem
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Specialized leaves

• Insectivorus plants
• Vines
• Succulents

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