[Footnote 23: Bul. 80: The commercial hickories, p. 50.]
[Footnote 24: Loc. cit.]
[Footnote 25: Although the factor of heart or sapwood does not influence the mechanical properties of the wood and there is usually no difference in structure observable under the microscope, nevertheless sapwood is generally decidedly different from heartwood in its physical properties. It dries better and more easily than heartwood, usually with less shrinkage and little checking or honeycombing. This is especially the case with the more refractory woods, such as white oaks and Eucalyptus globulus and viminalis. It is usually much more permeable to air, even in green wood, notably so in loblolly pine and even in white oak. As already stated, it is much more subject to decay. The sapwood of white oak may be impregnated with creosote with comparative ease, while the heartwood is practically impenetrable. These facts indicate a difference in its chemical nature.—H.D. Tiemann.]