1. Function External Anatomy Internal Anatomy Specialized Stems
STEMS: FORM & FUNCTION
Function
External Anatomy
Internal Anatomy
Specialized Stems

2. The Plant Body: Stems FUNCTION OF STEMS
Stems support leaves and branches.
Stems transport water and solutes between roots and leaves.
Stems in some plants are photosynthetic.
Stems may store materials necessary for life (e.g., water, starch, sugar).
In some plants, stems have become adapted for specialized functions.

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

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

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. EXTERNAL ANATOMY

8. EXTERNAL ANATOMY

9. STEM APICAL MERISTEM

10. Apical Dominance
Apical dominance refers to the suppression of growth by hormones produced in the apical meristem.  The Christmas tree pattern of pines indicates strong apical dominance.  Bushy plants have weak apical dominance.  If apical meristem is eaten or destroyed, plants may become bushy.
Lateral branch growth are inhibited near the shoot apex, but less so farther from the tip.
Apical dominance is disrupted in some plants by removing the shoot tip, causing the plant to become bushy.

12. PRIMARY & SECONDARY GROWTH

13. Monocotyledonous & Dicotyledonous Flowering Plants

14. Monocot Stem – cross section

15. INTERNAL STEM ANATOMY

16. Typical Stem Cross Section (Dicot Stem)
Helianthus annuus-
sun flower annual
Epidermis
Cortex
A ring of vascular bundles
Pith

17. Epidermis
- window, reduce water loss
Cortex Collenchyma
- extensible support
Cortex Parenchyma
- photosynthesis, etc.
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?

18. 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

19. Vitis vinifera - grape

20. 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.
Remnants of the procambium:
Intrafasicular cambium
Interfasicular cambium
Vitis vinifera - grape

21. If you have ever been to Washington DC you will see how the early architects and artists for governmental buildings were impressed with Greco-Roman architecture and symbols.
On each side of the seat occupied by the presiding officer of the Senate are two Fasces. The Romans had many symbols of Power.
One of them was a bundle of sticks lashed together in a cylinder with a long axe in the center. This is a Fasces! Early Botanists noted that the vascular tissue in stems appeared in discrete bundles which they called Fascicles!!!
Fasces => Fascicles (bundle). 
An area of Ground Tissue between the Fascicles was called Interfascicular! Remnants of the procambium between the primary phloem and xylem was called Intrafascicular.
Information obtained from: and

22. Fasces
Fasces (from the Latin word fascis, meaning bundle) symbolise summary power and jurisdiction, and/or "strength through unity.“
The traditional Roman fasces consisted of a bundle of birch rods tied together with a red ribbon as a cylinder around an axe.
One interpretation of the symbolism suggests that despite the fragility of each independent single rod, as a bundle they exhibit strength.
See:

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

24. Basswood – 1 & 2 years old

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

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

27. 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!

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

29. Anatomy of a Woody Stem

30. The trees pictured below have long lost their epidermis on the woody portion of the stem
Sequoia sempervirens - giant sequoia

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

32. 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

33. 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!

34. Modified & Specialized Stems

35. Food Storage Stems
Prickly Pear Cactus
Bamboo Shoots
Kohlrabi

36. Food Storage Stems - Sugarcane

37. Food Storage Stems - Asparagus

38. Rhizomes
Rhizomes - horizontal stems that grow below the ground with adventitious roots
Examples of plants that can produce rhizomes are irises, ferns, and grasses.

39. Stolons
Stolons or runners - horizontal stem that grows above the ground with long internodes
Examples of plants that can produce stolons are strawberry and airplane plants

40. Tuber Tubers - accumulation of food at the tips of underground stolons
The "eyes" of a potato are the nodes of a starch-ladened stem

41. History of the Potato
Potato first domesticated in region of modern day Bolivia and Peru
Failure of the potato crop in led to the Irish Potato Famine

42. Taters and Spuds

43. Rosette
Rosette - stem with short internodes and leaves attached at nodes

44. Wild Radish – Rosette & Bolt
A FLOWERING ANNUAL
YEAR ONE
YEAR ONE

45. Common Mullen – Rosette & Bolt
A FLOWERING BIENNIAL
YEAR ONE
YEAR TWO

46. Bulb
Bulbs - large buds with a small stem at the lower end surrounded by numerous fleshy leaves, adventitious roots at base
Examples include onion, tulip, and lily

47. Corm
Corms - resemble bulbs but composed entirely of stem tissue surrounded by a few papery scale like leaves, food storage organs with adventitious roots at the base of corms
Examples include crocus and gladiolus.

48. Cladophylls
Cladophylls - leaf-like stems; examples include butcher's broom, asparagus

49. Photosynthetic Stems
Cacti - stout fleshy stems that are modified for food and water storage and photosynthesis.

50. Thorns Honey locust (modified stem)
Black Locust (modified leaf stipules)

51. Tendrils
Grape Tendrils

52. Sugar Loading of Phloem and Bulk Flow

53. Sugar Loading of Phloem and Bulk Flow

54. Transpiration-Cohesion Hypothesis for Water Movement