1. Secondary Growth In Stems
Angiosperms VI
Secondary Growth
In Stems

2. What is secondary growth?
Growth in “girth” of woody plants
Tissues derived from cambial layers
VASCULAR CAMBIUM
produces secondary xylem and secondary phloem
CORK CAMBIUM (phellogen)
produces cork (phellem) and phelloderm tissues

3. Typical Woody Eudicot Stem (overview)
Periderm or “bark”
Vascular cambium
Secondary xylem
Pith

4. Woody Eudicot Stem

5. Typical Woody Eudicot Stem (detail)
Secondary xylem
Vascular cambium
Rays
Secondary phloem (including phloem fibers)
Cortex

6. Secondary Xylem (angiosperms)
Vessels
Fibers and tracheids
Wood rays
Growth rings (annual rings)

7. Secondary Xylem (“up close and personal”)
Fibers
Tracheids
Vessels
Ray parenchyma

8. “Growth Rings” Spring (Early) Wood Summer (Late) Wood
first cells produced by the vascular cambium
large cells (good growing conditions)
Summer (Late) Wood
smaller cells produced toward the end of the growing season
poor conditions (cooler, drier)
Radical change in cell size allows for recognition of annual “growth rings”

9. Bristlecone Pine (oldest of tree species in North America)
years old

10. Oak Wood in Section
Note: thick, multiseriate
wood rays

11. Other Variations Heartwood Sapwood darker in color
occupies center of the stem, more dense (stronger)
deposit of waste products such as resins, gums, oils, and tannins
Sapwood
lighter in color
outer layers, less dense (weaker)
contains the sap (dissolved nutrients and water)

12. Woody Stem and Periderm
sapwood
heartwood

13. Woody Twigs Terminal bud with bud scales Axillary buds Lenticels
Leaf scar

14. Twig Structures

15. Lenticels
Pores in the cork layers which allow for gas exchange in the periderm

16. Uses of Secondary Growth
Wood Products
Various uses based on the density of the wood (often in lbs./cubic foot)
Furniture, baseball bats, plywood, pulp products, musical instruments, particle board, artistic pieces, fuel
Other Products
rope, cinnamon, dyes, drugs (quinine), charcoal, cork, maple syrup

17. Cork Harvesting

18. 30-50 gallons of sap to make 1 gallon of syrup
Making Maple Syrup
30-50 gallons of sap to make 1 gallon of syrup