Meristem

Although the meristem is a tissue, it is treated separately due to its importance to plant growth and development.
The meristem is one or more cells which retain the ability to divide throughout the life of the plant.
The daughter cells from meristem may remain meristematic, or may differentiate to other tissues.
The ultimate meristem cell is the zygote or meio-spore.

• analogous to [animal] stem cells
• analogy overstated, and misleading
• [plant] meristem cell is superset of [animal] stem cell
• meristem = undifferentiated cells capable of dividing then differentiating
• most plant cells once differentiated retain the ability to dedifferentiate
• apical meristem, a.k.a. primary meristem
• direct descendants of meiospore
• differentiated to two types:
  shoot meristem
  root meristem
• 1^d division
• at slight angle to axis of filament
• each subsequent division rotated about 120^o
• should produce twisted 3-cell thick filament
• daughters become lateral meristem, a.k.a. secondary meristem
• division plane tangential to circumference of shoot/root
  alternating inward, outward
• 1^st division inward → vascular cambium
• 2^nd division outward → epidermis
• 3^rd division inward → ground meristem
• 4^th division outward → cork cambium
• primary growth = first growing season
• secondary growth = any growth beyond first growing season

tissues

dermal tissue

• epidermis
• hairs
  cellular on shoots
  cell extensions on roots
• cuticle of oil, wax
• bark
• cork (sometimes listed as ground tissue)

ground tissue

• mostly parenchyma
  undifferentiated tissue
• miscellaneous other nondescript tissues

vascular tissue

• xylem
  conducts water, mineral nutrients
• phloem
  conducts organic molecules [carbohydrates, hormones, amino acids, etc]
• rays
  lateral conduction within stem of some species

'organs' [another analogy to animals]

shoot system

• stem [primary shoot]
• dermal layer(s)
• phleom
• xylem
• pith (parenchymatous ground tissue)
• branch [secondary shoot]
• leaf [modified branch system]

root system

• primary root [tap root]
• dermal layer(s)
• xylem
• phloem
• secondary roots [branch roots, fiberous roots]

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© 2004-2005 TwoOldGuys ™

revised 19 aug 2006