The Shoot: Primary Structure and Development

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The Shoot Primary Structure and Development

• Chapter 25

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• True or False
• Shoots contain stems and leaves.
• Shoots are the above ground portion of the plant
  and are anatomically the same as roots.

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The Shoot

• Shoot- the above ground portion of the plant,
  consisting of stem and leaves.
• Stem- the above ground axis of vascular
  plants.
• Leaf- the principle lateral appendage of the
  stem.
• Foliage leaf- photosynthetic organ.
• Node- the part of the stem where one or more
  leaves are attached.
• Internode- the region of the stem between two
  successive nodes.
• Bud- an embryonic shoot protected by young
  leaves.

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Primordium- a leaf or bud in its earliest stage
of differentiation.
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Pith- the ground tissue occupying the center of a
root or shoot.
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Pith- the ground tissue occupying the center of a
root or shoot.
Corn
Alfalfa
Basswood
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Modified Stems

• Tendrils- modified leaves that spirally coil and
  aid in stem support.
• Stolons- runners stems that grow horizontally on
  the soil surface, often giving rise to new plants
  at the nodes.
• Thorns- hard, woody, sharp-pointed modified
  stems, arise from the axils of leaves.
• Spines- hard, woody, sharp-pointed modified
  leaves or leaf-parts.
• Prickles- a small non-woody, sharp-pointed
  outgrowth of bark or the epidermis.

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True or False. This is a tendril.
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True or False. This is also a tendril.
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• Given the following is a hard, woody,
  sharp-pointed modified stem that arises from the
  axils of leaves.
• True or False.
• This is a spine.

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Spines
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Prickles
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Underground Stems

• Rhizome- a horizontal stem that grows at or below
  the soil surface.
• Tuber- an enlarged, short, fleshy underground
  stem, forms at the tip of a rhizome. i.e. Potato.
• Bulb- a shortened underground stem covered by
  enlarged fleshy storage leaves. i.e. Onion and
  garlic.
• Corm- a thickened underground stem with small
  papery leaves. i.e. Gladiolus and Crocus.

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Leaf Arrangement

• Phyllotaxy- the arrangement of leaves on a stem.
• Basal- leaves are attached to an underground stem
  or rhizome.
• Opposite- 2 leaves attached at each node, borne
  on opposite sides of the stem.
• Alternate- 1 leaf attached at each node.
• Whorled- 3 or more leaves at each node.

Basal
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Leaf Morphology

• Blade- lamina.
• Petiole- stalklike portion.
• Stipules- scalelike or leaflike appendages at the
  base of leaves.
• Simple vs. Compound Leaves
• Simple- blades undivided.
• Compound- blades divided into leaflets.
• Pinnately compound- leaflets arising from both
  sides of the axis.
• Palmately compound- leaflets diverge from the tip
  of the petiole.

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Leaf Histology

• Mesophyll- the ground tissue of the leaf,
  specialized for photosynthesis.
• Palisade parenchyma- upper cells.
• Spongy parenchyma- lower cells.

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Hydrophyte- waterlily.
Xerophyte- oleander.
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Eudicot- random stomata.
Monocot- parallel stomata.
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Leaf Abscission

• Abscission- the normal separation of the leaf
  from the stem.
• Structural and chemical (ethylene) changes result
  in the formation of an abscission zone
• Separation layer
• Protective layer
• Magnesium ions, sugars, amino acids.