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14.—Radial longitudinal section of wood of oak (highly magnified). M.Str, medullary rays; Trach, tracheids; Gef (to the left), smaller pitted vessels; Librf, wood-fibers; H.P., wood-parenchyma. The large mass of tracheids to the left of the center of the figure lies over one of the broad pitted vessels. J.Gr, boundary of annual ring. (Kny.)