SECONDARY GROWTH - University of California, Davis · Roots also have secondary growth. Most...
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SECONDARY GROWTH
Transcript of SECONDARY GROWTH - University of California, Davis · Roots also have secondary growth. Most...
SECONDARY GROWTH
A Tilia stem before secondary growth
Pith rays (parenchyma)
Residual procambiumCell division starts to form cambium (meristem)
residual procambiumparenchyma
primary xylemprimary phloem
Cells begindividing
Vascularcambium
forms
Secondaryxylem and
phloemform
secondary xylem
secondaryphloem
vascular cambium
secondary xylemsecondary phloem
vascularbundle
residualprocambiumvascularbundle
primary xylemparenchyma
primaryphloem
interfascicularcambiumfascicularcambium
vascular cambium
secondary phloem
secondary xylem
secondary xylem
secondary phloem
vascular cambium
Developing cambium
Interfasicular cambium(from ray parenchyma)
fasicular cambium(from procambium)
xylem phloem
tylose
corkSpring wood Summer wood bark
tylosePith rays
cortex
cortex --> phellodermcork cambium
phellem
As the stem enlarges, theepidermis is broken, and must be renewed (asphellem/cork.
How many years’ growth?
xylem
heartwood
sapwood
phloem
cork
Tangential
Radial
TransverseSections
Roots also have secondary growth
Most monocots do not have secondarystem or root growth
Maizestem
Summary
Dicot stems (and roots) develop a vascular cambium,in which cell division produces new xylem and phloem
They also develop a cork cambium that produces cork(to replace epidermis) and phelloderm
Secondary xylem is the wood of commerce
