_"Forestry for Farmers," Fernow_, and other U. S. Forestry Division Publications, Vol. IX, Tenth U. S. Census; _Hough's American Woods (text)_; The Forester; The Northwestern Lumberman; The (New Orleans) Lumber Trade Journal; The New York Lumber Trade Journal; The Timber Trades Journal (London); "Lumber Trade of U. S." (Bureau Statistics U. S. Treas. Dept.); Trees in Winter, Huntington. HISTORICAL. Brockhaus, Konversations-Lexikon; Pliny, etc. MEDICINAL PROPERTIES. U. S. Dispensatory. Books particularly useful to beginners are in italics. Names are repeated when books could not be particularly classed under one heading. Also see foot-notes under subjects in questions. THE PRINCIPAL SPECIES OF WOOD. INTRODUCTION. A tree has been defined as a woody plant that produces naturally and in its native place one principal erect stem with a definite crown of foliage. A plant thus attaining to the dignity of a tree is said to be arborescent.[1] There are nearly five hundred distinct species of trees growing in the United States,[2] as well as many others peculiar to other countries, yet the great mass of wood everywhere utilized is derived from comparatively few of them.[3] Many woods will be more generally employed as their valuable properties become more familiar or as the supplies of wood now utilized continue to diminish. The same tree is often called by different common names in different places. Nearly thirty names are thus applied to the longleaf pine (_Pinus palustris_). Such confusion can be avoided only by regarding the recognized botanical nomenclature. The botanical name of a plant consists of two principal terms denoting genus and species. Quercus, for example, is [p002] the generic name including all species of oak. Alba, rubra, and others are specific names denoting the said species. Quercus alba and Quercus rubra are completed terms. Genera are not fixed but differ with authorities, so that the abbreviated name of the botanist responsible for the classification adopted is often added, as Quercus alba Linn. and Ulmus fulva Michx. A species is a collection of individuals that might well have sprung from some single root. A genus is a collection of related species. Genera are gathered into families. Families and genera differ with authorities. A variety includes individuals differing slightly from accepted species. Its name when existing is part of the specific name. "Quercus robur var. pedunculata" specifies a variety (pedunculata) of "red" or strong (robur) oak (Quercus). A variety of one botanist is sometimes a distinct species of another. The size and character of the trunk, and the range, locality, or distribution of the tree, have much to do with the utility of the wood, since large or perfect timbers cannot be derived from species characterized by small or crooked trees, and since wood is always more used if it is widely distributed so as to be easily available.[4]