1. Stem Lecture Functions Support of Leaves, Flowers, Fruits
Conduction of Water, Minerals, Sugars, etc.
Photosynthesis
Storage
Defense

2. Stems support a display of leaves.
Stems orient the leaves toward the light with minimal overlap among the leaves.
Asclepias - milkweed

3. The stem supports a display of flowers
Cercis canadensis - redbud

4. The stem supports a display of fruits.
The stem of a vine “twines” around objects in the environment - circumnutation!
Ipomoea nil - morning glory

5. The stem does photosynthesis…
and stores water.
Opuntia-prickly pear

6. This stem does photosynthesis, stores water, but also produces a defense chemical: mescaline…a hallucinogen.
Lophophora williamsii - peyote

7. Structure to Provide Functions
Stem Lecture
Structure to Provide Functions
Support of Leaves, Flowers, Fruits
Conduction of Water, Minerals, Sugars, etc.
Photosynthesis
Storage
Defense

8. Typical Stem Cross Section
Helianthus annuus-
sun flower annual
Epidermis
Cortex
A ring of vascular bundles
Pith

9. Epidermis
- window, reduce water loss
Cortex Collenchyma
- extensible support
Cortex Parenchyma
- photosynthesis, etc.
Phloem Fibers
- rigid support
Functional Phloem
- conduct sugars etc. away from leaf to rest of plant
Vascular Cambium
- adds 2° xylem and 2° phloem
Xylem
conduct water and minerals up from soil
Pith
water storage, defense?

10. VIP Stem: Provide both name and function labels:
Epidermis: reduce evaporation, gas exchange
Cortex: photosynthesis, collenchyma support
Vascular Bundles: conduction
Pith: water storage? defense? disintegrate?
outside
to center
Vascular Bundle:
outside
to center
Phloem Fibers: support
Functional Phloem:
conduct CH2O away from leaf
Vascular Cambium:
add 2° Xylem and 2° Phloem
Xylem:
conduct minerals up from soil

11. Vitis vinifera - grape

12. Notice how the vascular cambia of adjacent vascular bundles line up side by side.
Notice that cambium tissue differentiates between the bundles, connecting the cambia together.
Vitis vinifera - grape

13. The vascular cambium makes 2° tissues:
Vitis vinifera - grape
2° phloem
2° xylem

14. Each year the cambium produces a layer of secondary xylem and a layer of secondary phloem.
This photo shows secondary xylem from parts of three years in Pinus strobus (white pine).
spring of the next year
winter of that year
fall of that year
mid-summer of one year

15. Three years of Secondary Growth
Tilia - basswood
Secondary
Phloem
cambium
Secondary
Xylem

16. The study of the growth rings in wood: Dendrochronology

17. This tree is Pinus aristata (bristlecone pine).
One individual of this species shows more than 5000 growth rings!
Inner wood, harvested by boring, was used to validate carbon-14 dating.
Imagine the stories that this California tree could tell…perhaps something of migration of Asian peoples down the western coast of North America! They were contemporaries of Pharaohs!

18. The epidermis will be stretched and torn if not replaced
Sambucus canadensis - elderberry

19. A cork cambium differentiates and produces a periderm.
Epidermis
cutin
suberin
Cork Cells
Cork Cambium
Phelloderm

20. Over time, the epidermis dies.
The cork cells build up to for a thick layer for the bark of a tree. We use this to make stoppers for wine bottles and so on.
When suberin is fully developed, the cortex cells will eventually be in the dark. So these chloroplasts will lose their function!

21. The thick periderm can be quite thick and assist in survival of forest fires!
Sequoia sempervirens - giant sequoia
Randy is about six-feet tall!

22. The bark covers and stiffens the spines on many woody trees and shrubs.

23. Bark =
epidermis + periderm + cortex + phloem + vascular cambium
Wood =
secondary xylem only!
Pith =
a small percentage of tree diameter at maturity