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Secondary Growth in Stems
• Responsible for
increase in girth
(diameter)
• Allows for much
greater size and
volume
• Great commercial
value (wood and wood
products)
P. Alaback
Vascular cambium
1.
Lateral meristem forming vascular
tissues
2.
Innermost layer of bark, between the
xylem and phloem tissues.
3.
Grows both to the inside and to the
outside
•
•
4.
http://www.esb.utexas.edu/mauseth/weblab/webchap3par/3.2-5.htm
cells on inside = secondary xylem
cells to outside = secondary phloem.
NOTE: secondary differentiates
these new tissues from the primary
xylem and phloem, which derive
from the apical meristem
Derivation from the Apical Meristem
http://mason.gmu.edu/~jlawrey/biol304/biol304/notes/Image18.gif
Anatomy of the Vascular Cambium
A. Technically vascular cambium = cambial initials
1. difficult to distinguish between initials and their derivatives
2. refer to a cambial zone
B. vascular cambium meristematic cells - highly vacuolated
1. Fusiform initials - vertically elongated
2. Ray initials - horizontally elongated or squarish
C. Two possible planes of cell division
1. Periclinal division = new cells in front or behind the other
a. Yields 2o xylem and phloem
b. New cells toward the inside = xylem; cells to the outside =
phloem
2. Anticlinal division = cells side by side.
a. adds new cells to the vascular cambium as stem grows in girth
Fusiform vs. ray initials
Fusiform and ray cells form
FILES of cells – each file contains
a number of differentiating
elements.
AXIAL
Axial:
Longitudinal
translocation,
xylem & phloem
elements.
Fusiform
Radial: Lateral
translocation.
Carbohydrate from
phloem, to
parenchymatic (living)
tissue, water from
xylem to living tissues
as well.
Endarch
tangential face
Exarch
tangential face
RADIAL face
Ray
Exarch
tangential face
RADIAL
face
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
•Produces the radial (lateral)
transport system cells
•In xylem and phloem these are the
parenchyma
•Produces the axial (vertical)
transport system cells
•In xylem and phloem these are
the sieve-tube member,
companion cells, tracheids,
vessels, and fibers
•Can be storied (more advanced;
less common) or nonstoried
Nonstoried
Fusiform Initials
Storied Fusiform
Initials
Plant Anatomy CD
Vascular Cambium
A. Technically vascular cambium = cambial initials
1. difficult to distinguish between initials and their derivatives
2. refer to a cambial zone
B. vascular cambium meristematic cells - highly vacuolated
1. Fusiform initials - vertically elongated
2. Ray initials - horizontally elongated or squarish
C. Two possible planes of cell division
1. Periclinal division = new cells in front or behind the other
a. Yields 2o xylem and phloem
b. New cells toward the inside = xylem; cells to the outside =
phloem
2. Anticlinal division = cells side by side.
a. adds new cells to the vascular cambium as stem grows in girth
Activity of the Vascular Cambium
1. cambium active from spring to fall;
inactive in winter
• Larger xylem produced in spring vs fall
• Lead to gradual reduction in size of xylem
2. Pattern of yearly activity produces annual
rings in the xylem
3. Generally the xylem-producing cells are
more active than the phloem-producing
cells
Development of the Vascular Cambium
A. function is to produce secondary growth,
1. vascular cambium must be formed before secondary
growth can occur
B. Two regions of primary stem contribute to the
vascular cambium
1. Fasciscular cambium - meristem cells within
vascular bundle
2. Interfascicular cambium - meristem cells between
vascular bundles
Development of secondary vascular tissues
During primary growth, the
vascular bundles produce
PRIMARY vascular tissue.
These are the primary
phloem (proto + meta) and
primary xylem (proto and
meta).
The fascicular cambium
separates the two
tissues.
Remember: a fascicle is a vascular bundle
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
1.
Development commences at the fascicular cambium
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
Establishment of
Vascular Cambium
Trifolium Stem
Plant Anatomy CD
First activity is in the vascular bundle
2.
FCZ = fascicular cambial zone
Secondary xylem
Secondary phloem
FCZ
Secondary xylem and phloem are produced
by the fascicular cambium
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
Transverse
Vascular Cambium
2o Xylem
2o phloem
with callose
Radial
3
The interfascicular regions begins to develop a
cambium.
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
The interfascicular cambial area in
herbaceous stems does not activate,
thus does not produce new phloem or
xylem tissues
PX
MX
2X
2P
PPF
CZ
1P
3b
3a
A widening band of secondary
vascular tissue results.
CZ
4
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
http://www.uri.edu/artsci/bio/plant_anatomy/107.html
The functional vascular cambium
1. Becomes vascular cambium when the fascicular and
interfascicular cambium join to form a complete cylinder
around the stem
2. As soon as the cylinder is formed, vascular cambium
becomes active
a. divides on both the inner and outer surface of the vascular
cambium surfaces.
3. Activity of the vascular cambium
a. New xylem cells are formed inwardly and attached to the
previously produced xylem
b. New phloem cells are formed outwardly and are attached to the
previously produced phloem
The ring of secondary tissue is
Complete. The interfascicular and fascicular
cambia together form a vascular cambium
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
http://botit.botany.wisc.edu:16080/images/130/
What happens when a porcupine “girdles” a tree?
http://botit.botany.wisc.edu:16080/images/130/
Porcupines break
through the
outer bark,
usually near the
top of a tree,
and eat the
phloem.This
damages the
vascular
cambium and
may lead to the
death of the
tree.
http://www.biologie.uni-hamburg.de/b-online/library/webb/BOT201/Angiosperm/MagnoliophytaLab99/Oak3DColrLab500.jpg
Time for a Break!
What You See in Different Sections:
Orienting You For Lab
1. Transverse - cross section through middle:
1.
2.
end of vessels, tracheids and fibers
Long dimensions of rays
1.
2.
3.
Looking at the face of the vascular cambium!
Long sides of vessels
Rays are in cross section (see their ends)
1.
2.
Long sides of fibers, vessels, and sides of rays
Rays look like streaks running at right angles across the
lengthwise vessels and tracheids
2. Tangential - perpendicular to radius of stem:
3. Radial - cut parallel to direction of rays along
radius of stem:
Understanding
Sections
Tilia Stem (linden)
Tangential
Cross Section
Radial
Tilia Stem (linden)
Cross Section
vessels (1)
tracheids (2),
libriform fibers (3),
axial parenchyma (4) and (5)
uniseriate rays(6)
Multiseriate rays (7)
Tilia Stem
(linden)
Tangential
1 = tracheids with numerous tiny bordered pits in
their radial walls
2 = libriform fibers
3 = axial parenchyma
4 = narrow rays
Tilia Stem
(linden)
1 = vessel
3 = libriform fibers
5 and 6 rays
2 = tracheids
4 = axial parenchyma
Radial
What Kind of cell
makes up the bulk of
a tree?
NEXT
WEEK WOOD
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