INTRODUCTION.
Wood is an organic product--a structure of infinite variation of detail and design.[17] It is on this account that no two woods are alike--in reality no two specimens from the same log are identical.

There are certain properties that characterize each species, but they are subject to considerable variation.

Oak, for example, is considered hard, heavy, and strong, but some pieces, even of the same species of oak, are much harder, heavier, and stronger than others.

With hickory are associated the properties of great strength, toughness, and resilience, but some pieces are comparatively weak and brash and ill-suited for the exacting demands for which good hickory is peculiarly adapted.
[Footnote 17: For details regarding the structure of wood see Record, Samuel J.: Identification of the economic woods of the United States.

New York, John Wiley & Sons, 1912.] It follows that no definite value can be assigned to the properties of any wood and that tables giving average results of tests may not be directly applicable to any individual stick.
With sufficient knowledge of the intrinsic factors affecting the results it becomes possible to infer from the appearance of material its probable variation from the average.