. Wooden box and crate construction . e in identifying woods. Springwood and Summerwood The springwood is that part of the annual ring which isfirst formed each year. The wood is usually lighter in weightand softer because it contains more air spaces, that is, largercell cavities and less wood substance than that formed lateron in the year. As the season advances the cell walls formedare usually thicker and the cavities smaller so that the growthwhich is called summerwood is denser, harder, and oftendarker in color than the springwood. In some woods, such asmaple, birch, and basswood, there is
. Wooden box and crate construction . e in identifying woods. Springwood and Summerwood The springwood is that part of the annual ring which isfirst formed each year. The wood is usually lighter in weightand softer because it contains more air spaces, that is, largercell cavities and less wood substance than that formed lateron in the year. As the season advances the cell walls formedare usually thicker and the cavities smaller so that the growthwhich is called summerwood is denser, harder, and oftendarker in color than the springwood. In some woods, such asmaple, birch, and basswood, there is a little difiference betweenthe springwood and summerwood. In the case of spruce orhemlock the change from springwood to summerwood is grad-ual, but in oak and longleaf pine, for instance, the dififerencebetween springwood and summerwood is not only markedbut the change is very abrupt. It is often possible to estimatethe strength of wood by noting the percentage and density ofthe summerwood, STRUCTURE AND IDENTIFICATION OF WOODS 111. Fig. 29—Section (>\ western yellow pine log showing: radial surface, R;tangential surface, T; heartwood, H ; sapwood, S; pith, P. The annualrings are the concentric layers widest near pith and usually Iieconiing nar-rower toward the hark. The summer wood produces the dark lines thatstand out conspicuously on hoth the radial and tangential surfaces. 112 WOODEN BOX AND CRATE CONSTRUCTION The Structure of Hardwoods The name hardwood applies chiefly to woods which arecharacteristically hard and strong, such as oak, hickory andash. The hardwood group, however, includes some woodswhich are not relatively very hard, as, for instance, basswoodand popple. The real distinction on which the groupinginto hardwoods and softwoods is based is not the hardnessbut the structure of the wood. All the commercial hardwoods of the United States con-tain pores or vessels, cells which are strikingly larger than theother cells with which they are associated. The coni
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