1 Wood Chemistry PSE 406 Tree & Wood Structure

2 Agenda lTree components »Stem, crown, roots »Hardwood versus softwood lMacro wood structure »Reaction wood lMicro wood structure »Cell types »Cell wall layers

3 Why Wood Structure? lChemical distribution is dependent upon macro and microscopic structure. »Tree species dependent »Dependent upon position in tree »Cell type dependent »Dependent upon position in the cell

4 Tree Structure I lIt has been my experience that the majority of students taking wood chemistry can’t tell the difference between a hardwood and a softwood. In the next few slides I am going to present you with the layman's view of what is a tree.

5 Tree Structure II lIn general, trees contain these structural components: »Stump/Roots »Stem (wood & bark) »Crown: live/dead branches, foliage (leaves/needles), flowers and fruits. lThere are major chemical components which are found in all of these components. We will focus on the components found in the stem.

6 Tree Structure III lHardwoods »Trees containing leafs »Typically lose foliage in winter »Maple, alder, oak, lSoftwoods »Trees containing needles »Typically retains needles over winter. »Pines, firs, cedars, spruce

7 Tree Species Differences

8 Tree Composition 1. Values for branches, foliage, bark, and wood = % of tree above ground 2. Values for roots is a separate measurement = % of total tree

9 Macroscopic Structure Outer Bark (dead, protection, high extractives) Cambium (growth, inward wood, outward bark) Xylem =wood Phloem ( inner bark) (transportation of water and nutrients) Heartwood (support, dead, dark) Sapwood (younger, light color, living cells, transportation) Pith Annual Rings Earlywood Latewood Knot Definitions in notes section

10 Macroscopic Structure (2) Earlywood Latewood Heartwood Sapwood

11 Reaction Wood Tension Wood (Hardwoods) Compression Wood (Softwoods) Tension or Compression Wood This is a very poor representation of a very bent tree Notes

12 Wood Microscopic Structure lImagine that wood is made up of millions and millions of toilet paper rolls glued together. These rolls are the fibers that will make paper lMost often the ends of these tubes are sealed. There are small holes in the sides of the tubes to allow water to pass through

13 Microscopic Structure Microscopic structure of wood (Textbook of Wood Technology, Panshin, A. J., page 118 Tracheid (support, water transport, softwoods), in hardwoods we have libriform fibers) Resin canals (epithelium parenchyma secretes resin epithelium parenchyma secretes resin) Rays (transportation of water) Pits (wholes, transport between fibers, different typs)

14 Hardwood & Softwood Fibers lSoftwood Cells lSource: Wood Chemistry, Fundamentals and Applications. Sjostrom page 7 lHardwood Cells lSource: Wood Chemistry, Fundamentals and Applications. Sjostrom page 10

15 Microscopic Structure Structure of woody cell by Cote, This figure is used by almost every wood chemistry text. It can be found in Wood Chemistry, Fundamentals and Applications by Sjostrom on page 14. Notes ML-space between cells, 70-80% lignin, glue P-primary wall, very thin, random microfibrils, S (S1+S2+S3)-secondary wall, the thickest, microfibrils - opposite direction W-warty layer, thin, storage of metabolites

16 Cell Cross Section PrimarySecondary 1 Secondary 2 Secondary 3 Warty Layer Middle lamella

17 T/F l Earlywood: wide, thin walled cells for water transport (T/F)? l Phloem: this is where growth takes place in the stem (T/F)? l Heartwood: outer (younger) portion of the woody tissue (T/F)? l Cambium: this is the dead protective layer (T/F)?

18 T/F lVessels: short, wide, thin-walled cells found in hardwoods (T/F)? lIn hardwoods, epithelium parenchyma cells secrete resin (T/F)? l…………. are holes in the fibers which allow water to flow between fibers. lPrimary Layer: this is the thickest layer of the cell (T/F)?