49 



5S0 diameters and .Irawn Arith tl.o camera lucida. The sections were then allowed to dry under 

 the cover glass, to avoid any waipix-. and were a-ain .Irawn, when dvy, with every part occupy- 

 mg as nearly the same iK)sitiou in the tiel.l as the shruulien condition would allow. One cell wus 

 exactly superposed and served as a starting point. ISo difficulty was experienced in drawin- the 

 dried section; the])ictnre agreed with the sectiou on removal ofcov.T -lass, and also after ad^linrr 

 glycerine to the dried se.-ti..n. Left in glycerine a few weeks, the original picture could besuper"^ 

 posed (With the camera) almost but uot quite perfectly. Whether this liict is due to a ditterence 

 in swelling of wood in water and glycerine is not yet ascertained. 



The results so far obtained from tiiis study are in perfect agreement with the general theory of 

 shrink-ng. Thick walls shrink more than thin walls. The change of form and dimension of lumiua, 

 on the other hand, was found to be variable; some lumina changing their dimensions very markedly' 

 others scarcely or not at all. Lumina with circular cross-section appear to have changed less 

 than those with a compressed, slit like cross-sectiou ; in general the change was more apparent in 

 the summer wood than iu the spring wood. 



WOOD STRl-CTURE. 



The most time-robbing, but also the most fascinating, part of the work consists in the study of 

 the wood as an important tissue of a living organism; a tissue where all favorable and unfavorable 

 changes experienced by the tree during its long lifetime find a permanent record. 



GENERAIi APPEARANCE. 



For this study all the specimens from one tree are brought together and arranged in the same 

 order in which they occurred in the tree. This furiushes a general view of the appearance of the 

 stem ; any striking jieiuiliarities, such as great eccentricity of growth, unusual color, abundance of 

 resin in any part of the stem, are seen at a glance and are noted down. 



A table is prepared with separate columns, indicating — 



(1) Height of the disk in the tree, (this being furnished by the collector's notes); 



(2) Radius of the section; 



(3) Number of rings from iieriphery to center ; 



(4) Number of rings in the sap wood ; 



(5) Width of the sap wood ; and 



(6) Eemarks 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 gi-aiii 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 measiu-ed in groups of ten, twenty, thirty, rarely more, and the.se meas- 

 urements entered in separate subcolumus. In this way the rate of growth of the last ten, twenty, 

 or thirty years throughout the tree is found; also that of similar ])ei'iods previous to the last; in 

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

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

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

 grown to the heigiit from wliich 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 iu these rings, and the influence of such .seasons, 

 whatever their cause, both on the quantity and on the (piality or proi)erties 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 tliese rings is somewhat difficult. Zones of a <!entimeter and more exist where the 

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

 172-ti— No. t> 7 



