Primary growth, tissues and stem

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Review slides for root structure
Young and old buttercup root cs
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Zea root in cs showing endodermis and vascular
tissues
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Primary growth, tissues and stem
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PLANT TISSUES

• Simple tissues
• Epidermis
• Parenchyma
• Collenchyma
• Sclerenchyma
• Complex tissues
• Xylem
• Phloem

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Located just underneath the epidermis collenchyma
is characterized by localizedpectin rich wall
thickenings.
The pectin in the walls makes the walls plastic
instead of elastic.
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Sclerenchyma
Sclere has its root in a Greek word meaning
hard or rigid. Sclerenchymacells have thick
lignified secondary walls. It may be found
throughout themature plant. There are two basic
kinds based on shape. Fibers and sclereids.
Fibers are long and narrow usually with thick
walls.
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Fibers are usually found as a cap over a the
vascular bundles in a eudicot stem.
(Bundle cap)
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In cross section they showdense staining and a
smalllumen.
Cortical parenchyma
Cell wall
600 X
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Fibers in LS.
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Sclereids More isodimetric than fibersMany
different shapes. Found in leavesFruits, Seeds,
and Stems.
Astrosclereid in leaf (Water lilly)
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Sclereids in pear
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Xylem Conducting elements
Tracheids Primitive cells modified for water
conduction and support
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Vessel elements together make up a vessel
Modified tracheids with openings on their end
walls (perfotations)
Perforation plate
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Fiber
Vessel elements
Tracheid
Evolution of vesselelements and fibers
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Scanning electron micrograph of vessel element
perforationplate
pits
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Perforation plate in a more primitive
wood(Magnolia)
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Vessel member
Vessel
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Protoxylem vesselshowing helical thickenings
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Development of a vessel element
Dead cell withopen ends- partof vessel
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Sieve cells and sieve tube elements
Phloem

• These cells are modified to transport nutrients
  such as sucrose and other sugars. Unlike vessel
  elements.
• they are living cells with active metabolism,

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Sieve areascontaining plasmodesmata
Parenchyma
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Sieve tube elements are foundin Angiosperms.
They have sieveareas and a sieve plate on
theirend walls. When connected theyform a sieve
tube.
Sieve tube elements have losttheir nuclei and
are always associated with one or morecompanion
cells with nuclei.
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Sieve plate
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Sieve plate
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Development of a sieve tube element
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Shoots and primary growth
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Eudicot stem with narrow pith rays
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Eudicot stem with wide pith ray
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Monocot stem
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Eudicot stem with narrowpith rays
Cortex
Pith
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Open vascular bundlein Alfalfa stem cs.
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Vascular bundle
Monocot stem cs. (Zea)
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Closed vascular bundle In a buttercup stem 400X
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Development of vascular bundle in Zea