290 WOOD AND FOREST. 



to describe, individual observers differing especially in seeing and describing 

 shades of color. The same is true of statements of size, when relative, and 

 not accurately measured, while weight and hardness 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 Ala- 

 bama, and we can separate the white cedar, giant arbor vitae of the West 

 and the arbor vitse of the Northeast, only by the difference of the locality 

 from which the specimen comes. With all these limitations properly ap- 

 preciated, 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 ap- 

 pear in cross-section. They are: 



(1) Sap-wood and heart-wood (see p. 17), the former being the wood 

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



r 



ar-i 



.Sp.UV I r~SD\V. 



Fig". 128. "Non-porous" Woods. A, fir; B, "hard" pine; C, soft 



pine; ar, annual ring-; <?.<?., outer edge of ring-; i.e., inneredg-e 



of ring; s. zv., summer wood; sp. TV., 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 sap- 

 wood or heart- wood, 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 structure of their walls, especially projections and 

 spirals. 



(2) Annual rings, their formation having been described on page 19. 

 (See also Figs. 128-130.) They are more or less distinctly marked, and by 

 such marking a classification of three great groups of wood is possible. 



