60 



TIMBER. 



describing shades of color. The same is true of statements of size, 

 when relative, and not accurately measured, while weight and hard- 

 ness can perhaps be more readily approximated. Whether any feature 

 is distinctly or only indistinctly seen will also depend somewhat on 

 individual eyesight, opinion, or practice. In some cases the resemblance 

 of different species is so close that only one other expedient will make 

 distinction possible, namely, a knowledge of the region from which the 

 wood has come. We know, for instance, that no longleaf pine grows 

 in Arkansas and that no white pine can come from Alabama, and we 

 can separate the white cedar, giant arbor vitas of the West and the 

 arbor vitas of the Northeast, only by the difference of the locality from 

 which the specimen comes. With all these limitations properly appreci- 

 ated, 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 famil- 

 iarize himself before attempting to use the key, are mostly described as 

 they appear in cross section. They are: 



(1) Sap wood and heartwood (see p. 13), the former being the wood 

 from the outer and the latter from the inner part of the tree. In some 



ar-i 



Fig. 37.— " Non-porous " woods. A, fir; B, "hard" pine; O, soft pine; ar, annual ring; o. e., outer 

 edge of ring : i. e, inner edge of ring ; s. w., summer wood ; sp. w, spring wood ; rd, resin ducts. 



cases they differ only in shade, and in others in kind of color, the heart- 

 wood exhibiting either a darker shade or a pronounced color. Since 

 one can not always have the two together, or be certain whether he has 

 sapwood or heartwood, reliance upon this feature is, to be sure, unsat- 

 isfactory, 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 pres- 

 ence or absence of tracheids in pith rays and the structure of their 

 walls, especially projections and spirals. 



(2) Annual rings, their formation having been described on page 14. 

 (See also figs. 37-39.) 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 



