. Bulletin. Forests and forestry -- United States. GRAIN OF WOOD. 21 are too small to be distinguished. Studied with the microscope, each vessel is found to be a vertical row of a great number of short, wide tubes, joined end to end (fig. 9, c). The porous spring wood and radial gray tracts are partly composed of smaller vessels, but chiefly of tracheids like those of pine, and of shorter cells, the a wood paren- chyma," resembling the cells of the medullary rays. These latter, as well as the fine concentric lines mentioned as occurring in the summer wood, are composed entirely of short,
. Bulletin. Forests and forestry -- United States. GRAIN OF WOOD. 21 are too small to be distinguished. Studied with the microscope, each vessel is found to be a vertical row of a great number of short, wide tubes, joined end to end (fig. 9, c). The porous spring wood and radial gray tracts are partly composed of smaller vessels, but chiefly of tracheids like those of pine, and of shorter cells, the a wood paren- chyma," resembling the cells of the medullary rays. These latter, as well as the fine concentric lines mentioned as occurring in the summer wood, are composed entirely of short, tube-like parenchyma cells with square or oblique ends (fig. 9, a and b). The wood fibers proper, which form the dark, firm bodies referred to, are very fine, threadlike cells one twenty-fifth to one-tenth inch long, with a wall commonly so thick that scarcely any empty internal space or lumen remains (figs. 9, e, and 8, B). If instead of oak a piece of poplar or basswood (fig. 10) had been used in this study, the structure would have been found to be quite different. The same kinds of cell-elements, vessels, etc., are, to be. —Cross section of basswood (magnified), v, vessels; mr, pith rays sure, present, but their combination and arrangement is different, and thus from the great variety of possible combinations results the great variety of structure and, in consequence, of the qualities which distin guish the wood of broad-leaved trees. The sharp distinction of sap wood and heartwood is wanting; the rings are not so clearly defined, the vessels of the wood are small, very numerous, and rather evenly scattered through the wood of the annual ring, so that the distinction of the ring almost vanishes and the medullary or pith rays, in poplar, can be seen, without being magnified, only on the radial section. DIFFERENT GRAIN OF WOOD. The terms "fine grained," "coarse grained," "straight grained" and "cross grained" are frequently app
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