64 ECONOMIC WOODS OF THE UNITED STATES 



COLOK 



When wood is first formed it is almost, if not entirely, color- 

 less, as may be observed in the outermost growth rings in any 

 species. After a year or two it usually becomes yellowish, and 

 still later when changed into heartwood a decided deepening of 

 color results. Exceptions to this rule are rather numerous, for 

 example, Picea, Tsuga, Abies, Salix, Alnus, Betula, Ilex, and 

 JEsculus exhibit little or no contrast in color between heartwood 

 and sapwood. In all species the sapwood has a very limited 

 range of color and shade, but the heartwood exhibits great varia- 

 tion, from the chalky white of Ilex opaca to the ebony black of 

 old Diospyros virginiana, with practically all intermediate colors, 

 shades, and tints. In many woods the demarcation in color 

 between heartwood and sapwood is very sharp and distinct, while 

 in others the transition is gradual. In some instances {e.g., 

 Sequoia, Ilex, Catalpa, Cladrastis lutea) the color is uniform, 

 while in others (e.g., Liriodendron, Liquidambar, Swietenia) it is 

 variable not only in different specimens, but in different portions 

 of the same piece. The golden yellow of Toxylon shows narrow 

 streaks of red ; Liquidambar shows black streaks that usually give 

 the finished lumber a handsome watered effect; Liriodendron 

 varies from deep iridescent blue to yellowish brown; Robinia 

 varies from light straw-colored to deep golden yellow like Toxylon; 

 Taxodium is sometimes nearly black, often yellowish, reddish, 

 brown, or mottled. The deep-colored wood of Juniperus fre- 

 quently exhibits streaks of white sapwood, the intermingling 

 resulting from the fluted periphery of the stem. 



It is generally true that depth of color of woods is a criterion 

 of durability. Thus the dark heartwood of Juniperus, Sequoia, 

 Prosopis, Toxylon, Robinia, and Morus is very resistant to decay, 

 while that of Salix, Populus, Tilia, JEsculus, Acer, Fraxinus, and 

 Nyssa is perishable. The deeper color of the heartwood is due 

 to the infiltration or deposition in the cell walls and lumina of 

 gums, resins, pigments, tannin, and other substances. To these 

 is ascribed the greater durability of wood, since sapwood is 

 invariably not durable under exposure. In some instances, how- 

 ever (e.g., Chamcecyparis, Taxodium, Catalpa, Sassafras), the 

 infiltrated substances tend to prevent decay without greatly 

 deepening the color of the heartwood. 



