Pores belong to hardwoods only. The resin ducts in some softwoods present a similar appearance, but are far less numerous. All pores are, of course, situated in the annual rings, but in different species they are differently located as to spring and summerwood. In some woods the largest pores are in the springwood only and therefore run in rings. Such woods are called “ring porous,” and the oaks are best examples. In other species the pores are scattered through all parts of the ring in about the same proportion, and such woods are called “diffuse porous,” as the birches. Softwoods have no pores proper, and are classed “non-porous.” _Medullary Rays_--A smoothly-cut cross section of almost any oak, but particularly white oak and red oak, exhibits to the unaided eye narrow, light-colored lines radiating from the center of the tree toward the bark like spokes of a wheel. They are about the breadth of a fine pencil mark, and are generally a sixth of an inch or less apart. They are among the most conspicuous and characteristic features of oak wood, and are known as medullary or pith rays. Oak is cited as an example because the rays are large and prominent, but they are present in all wood, and constitute a large part of its body. They vary greatly in size. In some woods a few are visible unmagnified; but even in oak a hundred are invisible to the naked eye to one that can be seen. Some species show none until a glass is used. Some pines have fifteen thousand to a square inch of cross section, all of which are so small as to elude successfully the closest search of the unaided eye. The medullary rays influence the appearance of most wood. They determine its character. Oak is quarter-sawed for the purpose of bringing out the bright, flat surfaces of these rays. The prominent flecks, streaks, and patches of silvery wood are the flat sides of medullary rays. In cross section, only the line-like ends are seen, but quarter-sawing exposes their sides to view. That explains in part why some species are adapted to quarter-sawing and others are not. If no broad rays exist in the wood, as with white pine, red cedar, and cottonwood, quarter-sawing cannot add much to the wood’s appearance.