Many of the properties of wood depend upon the character and arrangement of the fiber cells which enter into its composition. This is especially true of those properties which determine its strength, hardness and adaptability for the manufacture of paper pulp. With a view to throwing light on these properties, we have made measurements of the length and diameter of the fibers in forty-one species of trees. No attempt was made to segregate the various types of fiber that occur in different species. We have taken any of the slender, fusiform, non-septate, thick walled members of the xylem. The maximum and minimum figures indicate that this lack of discrimination has not introduced any serious error. Were very critical discrimination attempted, the comparison of species would prove unduly complex, if not impossible
