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

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 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

Plant Anatomy CD

Nonstoried Fusiform Initials

Storied Fusiform Initials

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

Trifolium StemPlant Anatomy CD

Establishment of Vascular Cambium

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

Radial

Transverse

Vascular Cambium

2o Xylem 2o phloemwith callose

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

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 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://botit.botany.wisc.edu:16080/images/130/

http://botit.botany.wisc.edu:16080/images/130/

What happens when a porcupine “girdles” a tree?

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.

Time for a Break!

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

Understanding Sections

Tilia Stem (linden)

Cross Section

Tangential

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)

Radial

1 = vessel 2 = tracheids 3 = libriform fibers 4 = axial parenchyma5 and 6 rays

What Kind of cell makes up the bulk of a tree?

NEXT WEEK - WOOD