388 FORESTRY INVESTIGATIONS IT. S. DEPARTMENT OP AGRICULTURE. 



(3) Number of rings from periphery to center^ 



(4) Number of rings in the sapwood: 



(5) Width of the sapwood ; and 



(6) Remarks on color, grain, etc. 



The results from each disk occupy two lines, one for the pieces from the north side and one 

 for those of the south side. The radius is measured correct to one-half millimeter (0.02 inch), and 

 the figures refer to the air-dry wood. 



To count the rings, the piece is smoothed with a sharp knife or plane, the cut being made 

 oblique, i. e., not quite across the grain, nor yet longitudinal. Beginning at the periphery, each ring 

 is marked with a dot of ink, and each tenth one with a line to distinguish it from the rest. After 

 counting, the rings are measured in groups of ten, twenty, thiity, raiely more, and these meas- 

 urements entered in separate subcolumns. Tn this way the rate of growth of the last ten, twenty, 

 or thirty years throughout the tree is found, also that of similar periods previous to the last; in 

 short, a fairly complete history of the rate of growth of the tree from the time when it had reached 

 tlse height of the stump to the day when felled is thus obtained. Not only do these rings furnish 

 information concerning the growth in thickness, but indicating the age of the tree when it had 

 grown to the height, from which the second, third, etc., disks were taken, the rate of growth in 

 height, as well as that of thickness, is determined, any unfavorable season of growth or any series 

 of such seasons are found faithfully recorded in these lings, and the influence of such seasons, 

 whatever their cause, both on the quantity and on the quality or properties of the wood, can thus 

 be ascertained. 



In many cases, especially in the specimens from the longleaf pine, and from the limbs of all 

 pines, the study of these rings is somewhat difficult. Zones of a centimeter and moie exist where 

 the width of the lings is such that the magnifier has to be used to distinguish them. In some cases 

 this difficulty is increased by the fact that the last cells of one year's growth differ from the first 

 cells of the next year's ring only in form and not in the thickness of their walls, and therefore 

 produce the same color effect. Such cases frequently occur in the wood of the upper half of the 

 disks from limbs (the limb supported horizontally and in its natural position), and off en the magnifier 

 has to be leenforced by the microscope to furnish the desnecl information. For this puipose the 

 wood is treated as in all microscopic work, being fiist soaked in water and then sectioned with a 

 sharp knife or lazor and examined on the usual slide in watei or glycerin. 



The reason for beginning the counting of lings at the peripheiy is the same which suggested 

 the marking of all peripheral pieces by the letter a. It is convenient, almost essential, to have, 

 for instance, the thirty-fifth ring in Section II represent the same yeai's growth as the thirty-fifth 

 ring m Section X. The width of the sapwood, the number of annual rings composing it, as well 

 as the clearness and uniformity of the line separating the sapwood from the heartwood, are 

 carefully recorded. In the columns of u remarks'" any peculiarities which distinguish the particular 

 piece of wood, such as defects of any kind, the presence of knots, abundance of resin, nature of 

 the grain, etc., are set down. 



When finished, a variable number, commonly 3 to small pieces, fairly representing the wood 

 of the tree, are split off, marked with the numbers of their respective disks, and set aside for U\q 

 microscopic study, which is to tell us of the cell itself, the very element of structure, and of its 

 share in all the properties of wood. 



The small pieces aie soaked in water, cut with a sharp knife or razor, and examined in water, 

 glycerin, or chlonodide of zinc. The relative amount of the thick- walled, dark-colored bands of 

 summer wood, the resin ducts, the dimensions of the common tracheids and their walls, both in 

 spring and summer wood, the medullary rays, their distribution and their elements, are the 

 principal subjects in dealing with coniferous woods ; the quantitative distribution of tissues, or 

 how much space is occupied by the thick-walled bast, how much by vessels, how much by thm- 

 walled, pitted tracheids and parenchyma, and how much by the medullary rays; what is the 

 relative value of each as a strength-giving element ; what is the space occupied by the lumina, 

 what by the cell walls in each of these tissues — these aie among the important points in the study 

 of the oaks. 



Continued sections from center to periphery, magnified 25 diameters, are employed in finding 

 the relative amount of the summer wood; the limits of the entire ring and that of spring and 



