Secondary xylem, or wood, is put to an extremely wide variety of uses. The extensive range of species from the gymnosperms and angiosperms which are used as sources of wood is reflected in the diverse properties of the vari-ous kinds of wood.
There is archaeological evidence that our early ancestors were well aware of the best woods for burning for warmth or metal smelting, those most du-rable and strong for making boats or buildings and those most suited as shafts for tools or weapons. They even selected carefully for their musical instruments and decorative carvings. In our more advanced stage of tech-nology, we make use of the different characteristics of strength, workabili-ty, durability, appearance, density and pulping potential in our selection of woods for a vast range of primary and secondary products.
Obviously, this wide range of properties is a result of the variation in the histology and fine structure of woods. In fact, there are many characters in which wood can vary, but it is not always clear what effects they have on the properties of the wood. The possible variation is so great that the set of characters shown by wood from a particular species can provide clues to the identity of the species. Sometimes the set of characters may indicate only the family or genus, but occasionally it is confined to a species. In other words, one would expect individuals of the same species to share very simi-lar wood characters, but another closely related species might be so similar that it cannot be distinguished by wood features alone.
We shall explore the sorts of differences which occur in wood, and look at the ways in which these help in identification and in establishing therelationships between species, and how they affect the properties of the timber.
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