1. Vascular transport, mechanical support, storage: Plant stems (including vascular pathways, growth forms, woody/herbaceous)

2. Questions For plants, APweb characters page
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Discussion
Questions?

3. Ferns
Gymnosperms
Angiosperms

4. A digression into woody vs. herbaceous

5. Primary vs. Secondary growth

6. Groover. 2005. What genes make a tree a tree. TREE. 5:210

7. Plant stems
What are the functions of a plant stem?

8. Plant stems How do they accomplish these tasks? Phloem (living cells)
Xylem
Dead cells: Vessels, tracheids, fibers
Living cells: Parenchyma (axial and ray)

9. Transport: Water!

10. Evapotranspiration

11. Cohesion-tension

12. Conductivity increases to the fourth power of the radius
Perforation plates
Pits
Vessel elements
Diam: um, Vessel L: few mm to few m
Tracheid:
Diam: mm, L: ~1-5 mm

15. Embolisms What happens when air gets in?
Freeze- and drought-induced cavitation

16. Embolisms What happens when air gets in?
Drought-induced cavitation: air seeding

17. Woody and pseudo woody clades
Water conducting cells
Pits
Support
Living cells
Wood
Ferns
Tracheids, vessels
Homogenous
Sclerenchyma bands ?
Pseudo woody
Extant gymnosperms
Tracheids, except Gnetales
Torus/margo, with a number of exceptions
Tracheids
4-10% ray, 0% axial parenchyma
Woody, low density
Monocots (bamboos, palms)
Fibers, tracheids
Ground parenchyma
Basal angiosperms, Magnolids, Eudicots
Mainly vessels
Mainly homogenous
Fibers, sometimes tracheids
11-30% ray, up to 11% axial parenchyma
Woody, variable density

18. Evolution of vessels

19. Evolution of vessels
Angiosperms: have higher rates of CO2 uptake and transpiration. They have literally transformed their surroundings (more next week!)
To do this, they must be able to transport efficiently.

20. Peforation plates
Pits
Vessel elements
Tracheid

21. Question We know that derived angiosperm vessels are more efficient.
Were basal angiosperms with vessels more efficient than gymnosperms and vesselless angiosperms?

22. Herbs or pseudo woody
Tracheids, heterogeneous pits, *
Vessels, homogenous pits, fibers
Basal *
Derived
Herbs or pseudo woody *
* = vesselless *
Basal type with long thin vessels

23. Question We know that derived angiosperm vessels are more efficient.
Were basal angiosperms with vessels more efficient than gymnosperms and vesselless angiosperms?
Answer: At the level of a given unit of stem, NO!
So then what?

24. So, then what?
We know basal angiosperms vessels are more efficient than tracheids at the conduit level. Meaning?

25. Perhaps…
Less space needs to be devoted to vessels, so more diverse cell tissues can evolve or different allocation to tissues can arise… (Heteroxyly)

26. Why did vessels evolve?

28. Why did vessels evolve? Findings: In the basal angiosperm with vessels
Vessels did not confer greater transport efficiency at the stem level, nor greater photosynthetic ability
Vessels did allow for “uncoupling” of the hydraulic and mechanical support functions
Wood was denser and stems were stronger and energy per volume was greater in the species with vessels.
Also, species with vessels grew taller.

29. Why did vessels evolve? So…
Why vessels were first important (heteroxyly) appears to differ from why vessels may have led to the rise of the angiosperms (stem level efficiency)

30. From water to land: Evolution of tetrapod limbs

31.
Elpistostege