Transcript Cork Cambium

Secondary Growth
Chapter 5
Secondary Growth
• Secondary growth is an
increase in girth of a
plant initiated by cell
divisions in lateral
meristems.
• In woody plants,
primary growth occurs
simultaneously with
secondary growth.
Compare and Contrast
1° and 2 ° Growth
Primary
Secondary
1. Growth in length
1. Growth in girth
2. Apical or Intercalary
meristems (i.e.
protoderm, procambium,
and ground meristem)
3. Meristems are clusters of
undifferentiated cells
4. Occurs in regions of new
growth of the plant
2. Lateral or Secondary
meristems (i.e. vascular
cambium and cork
cambium)
3. Cylindrical meristems
4. Occurs in regions of a
woody plant where
primary growth has
ceased
Lateral Meristems
• Differentiated cells (from primary growth) revert to become
undifferentiated cells, forming the lateral meristems
(Cambium). (Latin cambire, “to exchange”. Cambium cells
have “exchanged” their previous roles for a new role of
dividing repeatedly for new growth.)
• Vascular Cambium: produces secondary xylem (to the
inside of the cylindrical meristem) and secondary phloem
(to the outside) (called “secondary” xylem and phloem to
distinguish it from the vascular tissue formed from the
procambium during primary growth.)
• Cork Cambium: produces new dermal tissue; also known as
phellogen (Greek phellos, “cork”, genos, “birth”)
• If the cork cambium did not form, the loss of the ground tissue and
epidermis would leave the tree without a protective outer covering
(water loss and infection would increase.)
Lateral Meristems:
Vascular Cambium
and
Cork Cambium
Secondary Xylem
• Expands the plant’s capacity to carry water and
minerals up from the roots
• Adds structural support
• New secondary xylem replaces old secondary xylem
that no longer conducts
• Only recently formed layers of secondary xylem
conduct water and minerals with the older primary
and secondary xylem tissue being inactive.
• Secondary xylem is the “wood” of a tree (Greek
xylon, “wood”)
• Vascular cambium produces much more secondary
xylem than secondary phloem
• Secondary Xylem is full
of lignin, a rigid
molecule in the cell wall
of secondary xylem,
which adds
considerable strength
to the cellulose
backbone of cell walls.
• Lignin constitutes up to
25% of dry weight of
wood and is the second
most common organic
compound on Earth,
cellulose being the first.
Lignin
Secondary Phloem
– Increases transport of food from the leaves to the
rest of the plant body
– Only recently formed layers of secondary phloem
conduct phloem sap, with the older primary and
secondary phloem tissue being inactive.
– Older phloem cells no longer conduct because
they are stretched and broken when new cells
produced by the vascular cambium push them
outward.
– Eventually becomes part of the bark
Bark
• Bark consists of all the tissues external to
the vascular cambium (everything outside
the wood)
• Two distinct regions in bark
– Inner bark: consists of living secondary phloem,
dead phloem cells, and any remaining cortex
(ground tissue)
– Outer bark: consists of dead tissue, including
dead secondary phloem and periderm
• (Periderm is protective tissue replacing the
epidermis of young plants, includes the cork.)
BARK!
Paper birch
(Betula
papyrifera)
Black oak
(Quercus
velutina)
Shagbark
hickory (Carya
ovata)
Sycamore, or
buttonwood
(Platanus
occidentalis)
Heartwood: old
layers of xylem
that no longer
transport water
Sapwood:
consists of
younger xylem
that actually
transports
water
-Point to the vascular cambium on this picture.
-Point to the cork cambium.
Growth rings
(“Tree rings”)
• Growth rings are visible
because of the distinction
between early wood
produced in spring and late
wood produced in late
summer or fall.
• Spring and early summer =
large cells with relatively
thin secondary cell walls
• Late summer and fall =
smaller cells with thicker
secondary cell walls
Annual rings
• Each annual ring in
wood generally
represents one year’s
increment of growth
• The number of rings
varies with the distance
above ground.
Dendrochronology
• Dendrochronology is the science method of dating
based on the analysis of patterns of tree-rings, often
has implications with climatic interpretation.
• (From the Greek dendron, “tree”, and chronos,
“time”)
• Tree rings reveal a tree’s age and details about
climate and human history. How?
• What would 20 thin rings and 2 thick rings indicate?
Dendrochrology cross-dating
• The analysis of tree ring patterns
to determine climate patterns, to
date archaeological artifacts,
etc… by matching ring-width
patterns between samples from
living trees and dead wood.
Dendrochrology cross-dating
http://www.youtube.com/watch?v=7v83X_3ENfU (First minute intro and
17:54-22:45)
Dendrochronology and
Environmental Studies
• Mastering Science- Lord of the (Tree) Rings:
What trees can teach us about environmental
historyhttp://www.youtube.com/watch?v=fFc
ENDkXrZA
• Tree Rings: Counting the years of global
warming.http://www.youtube.com/watch?v=v
qicp4PvHrY
Some Commercial Uses of
Wood and Bark
Paper made from
a liquid solution of
ground-up wood
Cork Cambium
• When secondary growth begins,
epidermis sloughs off and is
replaced with cork made by the
cork cambium.
• Cork is harvested to make... CORK!
Latex from various plants, used to make various
products including rubber (see p116 about rubber production)
Lumber!
Lectures built from the textbook,
Introduction to Botany, by Murray W. Nabors.