Tangpntial section of Persimmon iDiospyros 

 virf/iniana-Jj.). showing rays in lioriz(mtaI seria- 

 tion. Enlariiocl fifty diametors. 



Uadial section of Persimmon, sliowiu!^ tier-like 

 arrangement of rays, vessel segments, wood fibers 

 and wood parenchyma fibers. Knlarged fifty 

 diameters. 



Tangential section of Ohio Buckeye (Aesculus 

 glabta-WiU^.). showing typical irregular dispo- 

 sition of rays and vessel segments! Enlarged 

 fifty diameters. 



? \;jgOK>^^ogv-zv:;^w:o^x;^;!JiC>^^ 



Tier-Like Structure of Some W^oods f 



A feature of importance in llie identifieatipn of certain woods 

 and one that has been largely overlooked in American species is the 

 presence, on longitudinal sections, of fine, delicate cross lines or 

 stripes. They appear to best advantage on the tangential section 

 and in a few instances in tropical woods are so distinct as to be 

 conuiionly known as "ripple marks". The distance between these 

 markings varies from 0.11 to 0..50 mm., and is fairly constant for 

 a species. 



The American woods characterized by the cross strii)ings are yel- 

 low buckeye (^sculus ociandra-^larsih.) . persimmon (Diospyros vir- 

 giniana-Zi^) , mahogany (Swieteiiia ma/iof/o/it-Jacq.), basswood 

 (Tilia americana-h., T. jmbescensA'ri., T. hclrrophiilla-yent.) , and 

 liguumvitEe (Guaiacum sanctum-h.). Among tropical woods a very 

 large number show these markings. Good examples are the lignum- 

 vita; of commerce (Guaiacum ofpciimle-l^.), red sandalwood (Ptero- 

 carpus santahnus), narra (Pterocarint.s t(if/i<H.s-WiIld.), .lamaica- 

 Quassia (Picrasina cxcclsa-Planeh.) . 



In not all of the woods are the cross markings of e(|ual ilistinet- 

 ness. In yellow buckeya and mahogany they are plainly visible to 

 the unaided eye. In persimmon they are distinct after being once 

 observed, but are liable to be overlooked in casual examination. In 

 basswood the lines are near the limit of vision, but when the speci- 

 men is held so that the light is retlected from the surface at just 



the right angle, they can be seen, without a lens; in fact they are 

 less distinct with a small lens, but a reading glass is of assistance in 

 liringing them to view. In lignum-vita; the lines are very fine, but 

 under the lens show with great distinctness and regularity. 



in Mil .\merican species exhibiting cross-striping (except maliog- 

 any) the feature appears to be constant and is of considerable value 

 in distinguishing woods. In mahogany the feature is not so depend- 

 able, as the same jiiece of wood may show the markings in one 

 l)lace and not in another. When present, however, it will serve as 

 a means of distinguishing the true mahogany from its many substi- 

 tutes on the market. 



These cross stripes are due to one or more |iei-uliarities in the 

 structure of the wood. In most woods the rays are arranged irregu- 

 larly and are not uniform in size and shape. In yellow buckeye, 

 ligniun-vitsp, and many tropical woods, the rays are not only uniform 

 in size but are also arranged m horizontal series or tiers. This is 

 largely the case in persimmon and mahogany, but here there is less 

 regularity in the size of the rays. The general effect is much the 

 same, though the lines are somewhat wavy. 



In addition to the rays the wood cells — wood fibers, wood paren- 

 chyma fibers, vessel segments — are also in tier-like arrangement. 

 The resulting structure may be compared roughly to that formed by 

 placing bundles of toothpicks end to end and crowding them together 



Pi^i'fii 



'riin,L.'ciiIi.Tl s.M I HI, I ., , ., ... l-.d, ki.yt 

 hiK ryc(«H!/r«-MMrsli. I. sill. win;; rays in 

 tal scrintion. ICnlaraed fifty diameters. 



(Aescu- Radial seiii'ni "i l;ass«,"«l i liliii (imciicuiin- 



horlzon- L. ). showing vossel .segments, wood fibers and 

 wood parenchyma fibers in tier-like arransement. 

 but with no rays present. Enlarged fifty diam- 

 eters. 



Cross section nf (ihin lUickeye (.lr.«ei(/H.s 

 lyJulicu-Willd.i. showing ordinary spacing nf rays 

 and small gap wliere two rays were missed liy 

 plane t)f section. Enlarged fifty diameters. 



-3S— 



