PLATE II In these specimens from a virgin or first-year operation at Columbia, Miss., 1916, the bark appears at the top of the figure in all except figure 4. The 1916 ring or its incipient formation is shown next the bark. All the other rings shown were formed by the trees before turpentining began. AR, annual ring; SP, spring wood; SM, summer wood; T, tracheids or wood fibers; R, rays; and GP, groups of parenchyma cells or resin passages. FIG. 1.-An example of the condition of the tree on April 13, 1916. No wood or resiniferous tissue had fully differentiated, but cambial activity (preliminary stages of wood formation) is apparent (at C) next the bark. FIG. 2.-By June 13, 1916, at least 5 or 6 tracheids are apparent, and resiniferous tissue appears to be about to differentiate. In the first year several rows of wood cells usually formed before resin passages were produced. FIG. 3.-Specimen cut July 5, 1916. Numerous resin passages present developed early in the annual ring. Compare size of passages in the 1916 ring with size of those in the other rings. FIG. 4.-Tangential section through 1916 ring, showing longitudinal view of vertical resin passages (GP), formed in a turpentined tree. Also T, tracheids; R, ray parenchyma; FR, ray with horizontal resin passage; and X, a crossing of the vertical and horizontal resiniferous systems. FIG. 5. Specimen cut July 5, 1916. In the 1916 ring, forming next the bark, are tangential series including several resin passages. This very abundant formation of resin passages accompanies the wounding or turpentining. The exudation from these is shown in Plate III, figure 2. Longleaf pine as found in the southern United States of America is the species chiefly discussed and illustrated in the following pages as the typical producer of American naval stores. Botanically, it is classed in the division of the Spermatophyta, the subdivision of the Gymnospermae, the order Coniferales, and family Pinaceae. The structure of the wood, the principal subject of this research, as seen with the aid of the microscope in an end view or cross section made from a normal unturpentined specimen, is shown in Plates II, V, and VI. The yield of oleoresin, obtained when a tree is wounded, comes from the cells of the aggregates GP, Plate II, figures 3, 4, 5, and elsewhere. CAMBIUM. The cells of the wood and bark of the pine are formed by the division and differentiation of the cells of the cambium layer, which is situated between the bark and the wood (C, Pl. II, fig. 1). This layer is made up of thin-walled cells, which retain their power to divide and thus produce the new cells composing the yearly rings of bark and wood, respectively.1 11 ANNUAL RINGS. The layer of new wood formed each year on the outside of the woody core of a tree is known as an annual ring (AR, Pl. II, figs. 1, 2, 3, and 5.) In the pines in question it is conspicuously differentiated into two portions. The spring wood (SP) has thin-walled cells and large cavities, and forms early in the growing season. The summer wood (SM) has denser cell walls, and though it may begin to form as early as June, it generally develops in July, or, at the latest, August. The width of the annual ring and the amount and density of the summer wood formed are markedly influenced by turpentining, and serve as indicators of the effects of the various methods used. SAPWOOD AND HEARTWOOD. A varying number of the outermost annual rings of wood make up the sapwood. This is usually lighter in color than the heartwood, or central portion of the tree. The water solutions of the sap circulate through the sapwood, and it is in this region that the oleoresin exudes from certain cells (parenchyma) which are characteristically active. Each year a portion of the inner sapwood ceases to function and becomes dead heartwood; as a result the thickness of heartwood increases with the tree's age, but that of the sapwood remains, with relatively small variations, approximately the same. The walls of 11 It is the cambium that tears when the wood is separated from the bark cylinder in making a willow whistle. 87404-22- -2 |