Coleus stem tip

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Coleus stem tip
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Root systems

• Fibrous systems are characteristic of monocots
• Tap roots are typically found in dicots and
  gymnosperms

Fibrous
Tap
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• Examples of strong tap roots

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Root cap apical meristem

• Notice the pattern of cells that have been laid
  down by the apical meristem.

Wheat
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Root tip
Protoderm
Root cap
Procambium
Ground meristem
Apical meristem
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Root tip growth regions
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Three zones of the root tip
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Root hairs
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Arabidopsis
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Epidermal cells - root hairs
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Mycorrhizae

• Fungi can perform similar functions to root hairs
  in the more mature portion of the roots

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Dicot (Buttercup) root x-section

• The vascular tissue is in the center of the root

epidermis
cortex
Endodermis
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Vascular cylinder

• As in the stem, xylem is to the inside, phloem to
  the outside
• Endodermis surrounds the stele

cortex
xylem
phloem
endodermis
pericycle
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Endodermis
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Endodermis

• The Casparian strip blocks water and minerals
  from moving through the exoplast to the vascular
  tissues

Casparian strip
Cell wall
membrane
Plasmodesmata
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Vascular cylinder

• Pericyle (one cell thick) surrounds the vascular
  tissue

cortex
xylem
phloem
endodermis
pericycle
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Lateral roots

• Lateral roots arise from the pericycle
• Vascular tissue in the new root is connected to
  that tissue in the parent root.

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Monocot root x-section

• Pith is
• found
• in the
• center
• of
• monocot
• roots

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Monocot root close up
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Dicot secondary growth in root

• Vascular cambium is between the xylem and phloem
  extends to the pericycle

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Dicot secondary growth in root

• Like in the stem, xylem is formed to the inside,
  phloem to outside

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Vascular cylinder
cortex
xylem
phloem
endodermis
pericycle
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Root branching

• Note the grafting in the Beech roots

Ash
Beech
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N fixing nodules
Rhizobium nodules
Actinomycete on Alnus
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Prop roots
Banyan tree
Red Mangrove
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Epiphyte roots
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Specialty roots

• Manroot
• weighs 60 lbs. and stores water

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Pathway of water movement

• The endodermis regulates what ions enter the
  vascular tissues

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Water movement

• Water movement into the tissues of the plant
  follows the water potential gradient

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Absorption lag

• Caused by resistance in the water path in the
  root (water must pass through endodermis)
• When roots are cut off under water in an actively
  transpiring plant, absorption into the xylem
  increases.
• The lag may be great enough to cause mid-day
  closure of the stomata until the absorption rate
  catches up

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Root pressure

• Minerals actively pumped into the xylem lower
  water concentration
• Water diffuses into the xylem causing a pressure
  to build since the cells can not expand
• Water is forced up the xylem

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Leaf guttation

• Root pressure can cause guttation of water from
  the leaf, especially in small plants

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