AMERICAN WOODS. 



99 



FIG. 5. "King' porous" woods white oak ami hickory, a. r., annual ring; su. 

 (/., -minnier wood; #p. w,, spring wood : t>, vessels or pores; c. I., "concentric" 

 lines ; rt, darker tracts of hard fibers formi ng the tirni part of oak wood ; pr, 

 pith rays. 



appreciated, the key will be found helpful toward greater familiarity with the woods which are 

 more commonly met with. 



The features which have been utilized in the key and with which their names as well as their 

 appearance therefore, the reader must familiarize himself before attempting to use the key, are 

 mostly described as they appear in cross section. They are: 



(1) Sap wood and heartwood, the former being the wood from the outer and the latter from the 

 inner part of the tree. In some cases they differ only in shade, and in others in kind of color, 

 the heartwood exhibiting either a darker shade or a pronounced color. Since oue can not always 

 have the two together, or be certain whether he has sapwood or heartwood, reliance upon this 

 feature is, to be sure, unsatisfactory, yet sometimes it is the only general characteristic that can 

 be relied upon. If further assurance is 



desired, microscopic structure must be 

 examined; in such cases reference has 

 been made to the presence or absence 

 of tracheids in pith rays and the struc- 

 ture of their walls, especially projec- 

 ions and spirals. 



(2) Annual rings. They are more 

 or less distinctly marked, and by means 

 of such marking a classification of three 

 great groups of wood is possible. 



(3) Spring wood and summer wood, 

 the former being the interior (first 



formed wood of the year), the latter the exterior (last formed) part of the ring. The proportion of 

 each and the manner in which the oue merges into the other are sometimes used, but more 

 frequently the manner in which the pores appear distributed in either. 



(4) Pores, which are vessels cut through, appearing as holes in cross section, in longitudinal 

 section as channels, scratches, or indentations. They appear only in the broad-leaved, so called, 

 hard woods; their relative size (large, medium, small, minute, and indistinct, when they cease to 

 be visible individually by the naked eye) and manner of distribution in the ring being of much 

 importance, and especially in the summer wood, where they appear singly, in groups, or short 

 broken lines, in continuous concentric, often wavy, lines, or in radial branching lines. 



(5) Eesiu ducts (see fig. 4), 

 which appear very much like 

 pores in cross section, namely, 

 as holes or lighter or darker 

 colored dots, but much more 

 scattered. They occur only in 

 coniferous woods, and their 

 presence or absence, size, num- 

 ber, and distribution are an 

 important distinction in these 

 woods. 



FIG. 6. " Diffuse porous " woods, ar, annual ring; ]ir, pith rays, which are " broad" at a. -n-j.*. 12 ^-\ 



'.inc-ati.-indistinct-atrf. (6) PlthrayS (866 fig. 6), 



which in cross section appear 



as radial lines, and in radial section as interrupted bauds of varying breadth, impart a peculiar 

 luster to that section in some woods. They are most readily visible with the naked eye or with a 

 magnifier in the broad-leaved woods. In coniferous woods they are usually so fine and closely 

 packed that to the casual observer they do not appear. Their breadth and their greater or less 

 distinctness are used as distinguishing marks, being styled fine, broad, distinct, very distinct, 

 conspicuous, and indistinct when no longer visible by the naked (strong) eye. 



(7) Concentric lines, appearing in the summer wood of certain species more or less distinct, 

 resembling distantly the lines of pores but much finer and not consisting of pores. (See fig. 5). 



Of microscopic features, the following only have been referred to: 



(8) Tracheids. 



. Beech ! Sycamore 



Birch. 



