1. Into the Wood(s):
What is wood, anyways?

2. What is wood made of? Cellulose Repeating pattern of modified starch
High tension strength
Lignin
Randomly crosslinked
phenolic polymers
Compression resistant

3. What is wood made of? Heartwood Darker wood in center
Dead cells, no transport
Adds structural strength
Sapwood
Lighter wood around edge
Transports water up (xylem)
Living cells

4. What is wood made of? Concentric layers – outside to inside:
Outer bark – protects from injury
Phloem (inner bark) – photosynthates (sugars) flow down from leaves to roots. Phloem is “leaky”.
Cambium – thin layer of dividing cells where most radial growth occurs. Cambium grows a new layer of sapwood every year; these are the growth rings
Xylem (sapwood) – water and nutrients drawn up from roots to leaves. Xylem is not “leaky”.

5. How does water move? Xylem cross-section:
Small diameter for more capillary effect
Xylem diameter inverse to tree height potential
Water is pulled from the roots to the leaves by wicking (evaporation from leaves) and capillary action

6. How does water move?
Xylem
Phloem
Some water evaporates, keeping leaf cool and creating a pressure deficit, which draws more water up from roots
(much like sucking on a straw)
Some water molecules
are split apart in photosynthesis to create glucose, but that’s for another day.
Xylem in leaf has pores, allowing water to permeate leaf interior

7. How does water move?
Xylem
Phloem
Water permeating the leaf interior absorbs sugars produced by photosynthesis
The phloem tubes in leaves allow sugar-laden water in, but not out. It flows downward (or outward) and is distributed by osmotic pressure to areas of the plant lacking sugar.
Phloem tubes

8. Where does water move? To leaves: Photosynthesis Transpiration Sap
To areas of growth:
Apical buds
Cambium
Root tips

9. Sap vs. pitch Pitch is the thick sticky resin that defends the plant
Resin canals
Pitch is the thick sticky resin that defends the plant
from injury and insects
- Source of turpentine, amber
-Antiseptic
Sap is the water carrying nutrients or sugars moving up through xylem or down through phloem

10. Bark Products from bark: Cork Cinnamon Quinine Outer bark Lenticels
Inner bark (cork)
Cork cambium
Phloem
Vascular cambium
Xylem (sapwood)
Products from bark:
Cork
Cinnamon
Quinine

11. Trees in fire-prone ecosystems have thick fire resistant bark

12. Bark protects trees from insects,
Pitch moth
Bark protects trees from insects,
to a certain extent
Bark beetle

13. Questions?