Post on 21-Dec-2015
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• cells on inside = secondary xylem• cells to outside = secondary
phloem.
4. NOTE: secondary differentiates these new tissues from the primary xylem and phloem, which derive from the apical meristem
http://www.esb.utexas.edu/mauseth/weblab/webchap3par/3.2-5.htm
Anatomy of the Vascular Cambium
A. Technically vascular cambium = cambial initials1. 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 elongated2. 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 phloemb. New cells toward the inside = xylem; cells to the
outside = phloem2. Anticlinal division = cells side by side.
a. adds new cells to the vascular cambium as stem grows in girth
Fusiform vs. ray initials
RADIAL face
Exarchtangential face
Fusiform and ray cells form FILES of cells – each file contains a number of differentiating elements.
Endarch tangential face
Plane
of cel
l div
isio
n
RADIAL face
Exarch tangential face
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
TANGENTIAL
RADIAL
AXIAL
Axial: Longitudinal translocation, xylem & phloem elements.
Radial: Lateral translocation. Carbohydrate from phloem, to parenchymatic (living) tissue, water from xylem to living tissues as well.
Fusiform
Ray
•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
Vascular Cambium
A. Technically vascular cambium = cambial initials1. 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 elongated2. 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 phloemb. New cells toward the inside = xylem; cells to the
outside = phloem2. 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
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
Development of secondary vascular tissues
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
Development commences at the fascicular cambium
1.
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
Secondary xylem and phloem are produced by the fascicular cambium
Secondary phloem
Secondary xylem
FCZ
2.FCZ = fascicular cambial zone
First activity is in the vascular bundle
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
The interfascicular regions begins to develop a cambium.
3
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
CZ
4
A widening band of secondary vascular tissue results.
1P
2PCZ
2X
MX
PX
PPF
3a
3b
The interfascicular cambial area in herbaceous stems does not activate, thus does not produce new phloem or xylem tissues
http://anubis.ru.ac.za/virtualplant/Powerpoint/cambial%20grow.ppt
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 activea. 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
CZ
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://www.biologie.uni-hamburg.de/b-online/library/webb/BOT201/Angiosperm/MagnoliophytaLab99/Oak3DColrLab500.jpg
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.
What You See in Different Sections:Orienting You For Lab
1. Transverse - cross section through middle: 1. end of vessels, tracheids and fibers2. Long dimensions of rays
2. Tangential - perpendicular to radius of stem:
1. Looking at the face of the vascular cambium!2. Long sides of vessels3. Rays are in cross section (see their ends)
3. Radial - cut parallel to direction of rays along radius of stem:
1. Long sides of fibers, vessels, and sides of rays2. Rays look like streaks running at right angles across
the lengthwise vessels and tracheids
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)
Radial
1 = vessel 2 = tracheids 3 = libriform fibers 4 = axial parenchyma5 and 6 rays