Plant Structure

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Plant Structure
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Plant Structure

• Roots, stems, leaves, flowers, and fruits make up
  the plant body
• Tissues of plants are composed of cells forming a
  structural unit
• The three tissue systems
• ground tissue
• the vascular tissue (conduction)
• dermal tissue (covering the body)

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Organs

• Roots, stems, leaves, floral parts and fruits are
  organs
• The tissue systems of the root and shoot are
  connected
• Tissues are developed as the plant grows

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Ground tissue

• Made up of three tissues
• Parenchyma
• thin walls
• food storage
• photosynthesis
• alive at maturity

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Ground tissue

• Made up of three tissues
• Parenchyma
• Collenchyma
• uneven wall thickenings
• provide support
• alive at maturity

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Ground tissue

• Made up of three tissues
• Parenchyma
• Collenchyma
• Sclerenchyma
• Secondary wall thickening (lignin)
• Dead at maturity
• Sclerids, Fibers

Broad bean stem x-section
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Vascular tissue - xylem

• Conducts water and dissolved materials
• Composed of four cell types
• Vessels (angiosperms)
• dead at maturity

xylem vessels
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Vascular tissue - xylem

• Conducts water and dissolved materials
• Composed of four cell types
• Vessels (angiosperms)
• dead at maturity
• pits found in walls

xylem vessels
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Vascular tissue - xylem

• Tracheids (Gymnosperms and angiosperms)
• Tend to be narrower and longer than vessels
• Fibers and parenchyma are also found in the xylem

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Vascular tissue - phloem

• Conducts dissolved sugars throughout plant
• Sieve tube members are the conducting cells
• Sieve plates are at the ends
• Alive at maturity
• most organelles (including nucleus) have
  degenerated
• Companion cells are adjacent to tube members

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Vascular tissue location

• Vascular tissue runs the length of the plant
• Xylem always to the inside of phloem

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Dermal tissue - epidermis

• Single layer in herbaceous plants
• Made up of parenchyma cells
• Have thickened layer on outer margin
• Waxy cuticle on surface
• Typically nonphotosynthetic and transparent
• Woody plants have a much thicker layer and
  replace epidermis with periderm over time
• Cork cells (dead at maturity) and cork parenchyma
  cells

Onion epidermis
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Meristems

• Located at tips
• increase length
• produce primary tissues
• Located near outside
• increase girth
• produce secondary tissues

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Plant Growth

• Growth includes
• cell division (mitosis)
• at meristems
• cell elongation
• back from meristem
• cell differentiation
• back from area of elongation

Central vacuole
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Secondary growth
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Woody twig morphology
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Dicot primary vascular tissue

• Secondary growth produces xylem phloem from the
  vascular cambium

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Alfalfa (Medicago) cross section

• This is actually an herbaceous plant that has
  secondary growth

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Vascular tissue location

• Monocots have scattered vascular bundles

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Vascular cambium

• Thin walled cells
• Keep ability to divide

Medicago
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Between vascular bundles (interfasicular cambium)

• Note the cells undergoing division in the cambial
  area

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Growth from the cambium

• Xylem is left behind and phloem is pushed
  outward and crushed

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Secondary tissues

• rays
• (parenchyma) are also formed

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Woody stem cross section
Secondary phloem

• Xylem forms most of the tissue in a woody stem

Xylem
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Spring and Summer Wood

• Spring growth creates larger vessels
• More dense wood comes in fall

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Annual rings

• Occurs mostly in temperate areas

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Tree rings

• Tree rings are simply growth cycle rings and
  may be formed one or more each year.

Pine Wood
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Oak cross section

• Notice how much more prominent the rays of the
  Oak are than that of Pine

Oak
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Branches

• Branches accumulate wood around them as they age
• A dead branch does not grow with the stem and
  creates a knot

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Wood density

• Density
• depends
• on the
• size of
• the cells

Tulip tree
Sugar Maple
Oak
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Vascular connections

• The vascular column is continuous from root to
  leaf

vein
pith
bud
leaf traces
leaf gap
cortex
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Xylem connections

• Both pits and openings at ends of cells allow
  fluid transport

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Ploem cells

• Parenchyma cells surround the sieve tube members
• Each sieve tube member has a companion cell

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