1. Secondary Growth in Stems
P. Alaback
Responsible for increase in girth (diameter)
Allows for much greater size and volume
Great commercial value (wood and wood products)

2. Vascular cambium Lateral meristem forming vascular tissues
Innermost layer of bark, between the xylem and phloem tissues.
Grows both to the inside and to the outside
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

3. Derivation from the Apical Meristem

4. 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

5. Fusiform vs. ray initials
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 and ray cells form FILES of cells – each file contains a number of differentiating elements.
Fusiform
Endarch
tangential face
Exarch
tangential face
Ray
RADIAL face
RADIAL
face
Exarch
tangential face
Plane of cell division

6. 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

7. Nonstoried Fusiform Initials
Plant Anatomy CD

8. 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

9. Activity of the Vascular Cambium
cambium active from spring to fall; inactive in winter
Larger xylem produced in spring vs fall
Lead to gradual reduction in size of xylem
Pattern of yearly activity produces annual rings in the xylem
Generally the xylem-producing cells are more active than the phloem-producing cells

10. 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

11. 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

12. Development commences at the fascicular cambium 1.

13. Establishment of
Vascular Cambium
Trifolium Stem
Plant Anatomy CD

14. 2. First activity is in the vascular bundle
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

15. Transverse
Vascular Cambium
2o Xylem
2o phloem
with callose
Radial

16. The interfascicular regions begins to develop a cambium.3

17. A widening band of secondary vascular tissue results.CZ 4
A widening band of secondary vascular tissue results. 1P 2P 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

19. 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

20. The ring of secondary tissue is CZ
The ring of secondary tissue is
Complete. The interfascicular and fascicular cambia together form a vascular cambium

23. What happens when a porcupine “girdles” a tree?

24. 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.

25. Time for a Break!

26. What You See in Different Sections: Orienting You For Lab
Transverse - cross section through middle:
end of vessels, tracheids and fibers
Long dimensions of rays
Tangential - perpendicular to radius of stem:
Looking at the face of the vascular cambium!
Long sides of vessels
Rays are in cross section (see their ends)
Radial - cut parallel to direction of rays along radius of stem:
Long sides of fibers, vessels, and sides of rays
Rays look like streaks running at right angles across the lengthwise vessels and tracheids

27. Understanding Sections

28. Tangential
Tilia Stem (linden)
Cross Section
Radial

29. Tilia Stem (linden)
Cross Section
vessels (1)
tracheids (2),
libriform fibers (3),
axial parenchyma (4) and (5)
uniseriate rays(6)
Multiseriate rays (7)

30. 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)
Tangential

31. 1 = vessel = tracheids
3 = libriform fibers = axial parenchyma
5 and 6 rays
Tilia Stem (linden)
Radial

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

33. NEXT WEEK - WOOD