WOODS COMPARED WITH STONES AND METALS.
Information relating to the general properties of wood compares in importance with information relating to the general properties of steel, stone, and cement. Engineers use more wood than any other set of men, yet general facts about wood, aside from those relating to its strength, are often relegated to the consideration of the botanist or the forester.
The consumption of wood has never decreased, although metals and stones have been substituted for it in many positions. In England, the consumption per capita more than doubled in the fifty years preceding 1895, in spite of the fact that nearly all of the wood used in that country had to be imported. In 1905, the total yearly mill value of wood products in the United States Was over nine times as great as the combined product of gold and silver, and twice as great as the value of the wheat crops.' The importance of wood as a material of construction is well expressed in the quotation that "Wood is an indispensable part of the material structure upon which civilization rests; and it is to be remembered always that the immense increase of the use of iron and substitutes for wood in many structures, while it has meant a relative decrease in the amount of wood used, has been accompanied by an absolute increase in the amount of wood used. More wood is used than ever before in our history." Wood is preferred because it is easily worked and light in weight. In many positions, it is as durable as iron. When dry it is a poor conductor of heat and electricity and is stronger than is commonly supposed. The tensile strength of a bar of hickory may exceed the tensile strength of a similar bar of wrought iron of the same length and weight.' However, wood is not homo geneous like metal and most of the stones that are used for build ing, but is so variable that several parts of the same tree often exhibit widely different qualities.
Most wood is used in construction; that is, in mines, railways, houses, and ships where size or quantity is required and where finish and appearance are less important. Much wood is used in cabinet work and in positions where appearance, appropriateness, and finish are important. Such woods are more in evidence, but the amounts used are actually very much smaller than the amounts used in construction. Some wood is required for turnery, carv ings, and implements that demand exact qualities that can be secured in small pieces only. Some wood is used indirectly, and in the manufacture of paper-pulp, gunpowder, and *chemicals. There are also by-products of trees, such as tanbark, turpentine, resin, and sugar.
Woods appear to be more numerous than they actually are, because more than one name is so often applied to the same species. Supplies are often brought from far distant places when woods of the same kind are available nearby, but are not recognized because they are called by differ ent names. One species, the Southern, Yellow, Georgia, or Longleaf Pine (Pins palustris), has nearly thirty local names. Such confusion can be avoided only by regarding the recognized botanical nomenclature.
Not only is it true that several names are often applied to the same wood, but, strange as it may seem, a fairly constant single product is sometimes derived from several unrelated species. The single name cedar is thus applied to several species of durable characteristically scented woods, which have similar anatomical features and which are derived from species that are not closely related to one another.
The botanical name of a plant is made up of terms denoting genus and species. For example, Quercus is the generic name that includes all the species of oak, while alba and rubra are specific names that apply to two particular species of the genus Oak. Quercus alba and Quercus rubra are completed names. The names of species are not fixed, but differ with authorities so that it is often best to add the abbreviated name of the botanist responsible for the name employed. Illustrations would be Quercus alba Linn., Quercus rubra Linn., and Ulmus fulva Michx.
A genus may be defined as a collection of related species, and a species may be regarded as a collection of individuals that might easily have sprung from some single stem. Genera are grouped into families, and both genera and families differ with authorities. The term "variety" is applied to individuals that differ less from one another than do species. Quercus robur var. pedunculata indicates a variety (var. pedunculata) of a certain species (robur) of Oak (Quercus). It should be noted that the variety of one botanical authority is sometimes regarded as a distinct species by another botanical authority.
About five hundred species of trees grow in the United States' and many other species grow in other countries, yet, the great mass of wood that is used in construction comes from compara tively few of these species. Sudworth excludes all but one hundred sources in his "Trees of the United States Important to Forestry," while a United States Treasury Department Sum mary contains the statement that but sixteen (16) kinds of hard wood were quoted in the Chicago markets on the first day of September of the year The statement is also made in the source referred to, that the prin cipal timbers of commerce in the United States are the genera known popularly as pine, fir, oak, hickory, hemlock, ash, poplar, maple, cypress, spruce, cedar and walnut.
Conditions are changing. The original forests are much smaller than in former years. Many woods that were once common are now scarce, while other woods that were once unfamiliar are now employed.
Botanical Classification of Trees and Their Woods.
Botanists group trees as they do other seed-bearing plants, mainly upon the characteristics of parts other than the trunks. In such groups, the flowers, fruit, and leaves are fundamentally important. A general classification is as follows: