chapter  2
24 Pages

Structure and Function of Wood

Wood is a complex biological structure, a composite of many cell types and chemistries acting together to serve the needs of a living plant. Attempting to understand wood in the context of wood technology, we have often overlooked the basic fact that wood evolved over the course of millions of years to serve three main functions in plants-conduction of water from the roots to the leaves, mechanical support of the plant body, and storage and synthesis of biochemicals. There is no property of wood-physical, mechanical, chemical, biological, or technological-not fundamentally derived from the fact that wood is formed to meet the needs of the living tree. To accomplish any of these functions, wood must have cells that are designed and interconnected in ways suf‹cient to

2.1 Introduction ............................................................................................................................9 2.2 Trees ..................................................................................................................................... 10 2.3 Softwoods and Hardwoods ................................................................................................... 11 2.4 Sapwood and Heartwood ...................................................................................................... 11 2.5 Axial and Radial Systems..................................................................................................... 13 2.6 Planes of Section ................................................................................................................... 13 2.7 Vascular Cambium ............................................................................................................... 15 2.8 Growth Rings ........................................................................................................................ 16 2.9 Cells in Wood ....................................................................................................................... 17 2.10 Cell Walls ............................................................................................................................. 18 2.11 Pits ........................................................................................................................................ 19 2.12 Microscopic Structure of Softwoods and Hardwoods .......................................................... 21

2.12.1 Softwoods ............................................................................................................... 21 2.12.1.1 Tracheids ................................................................................................ 21 2.12.1.2 Axial Parenchyma and Resin Canal Complexes ...................................22 2.12.1.3 Rays ........................................................................................................23