KEY TO THE MORE IMPORTANT WOODS OF NORTH AMERICA. 



[The numbers preceding names refer to the List of Woods following the Key.] 



I Non-porous woods — Pores not visible or conspicuous on cross section, even 

 with magnifier. Annual rings distinct by denser (dark colored) bands of summer 

 wood (fig. 37). 



II. Ring-porous woods, — Pores numerous, usually visible on cross section with 

 out magnifier. Annual rings distinct by r zone of large pores collected in the spring 

 wood, alternating with the denser summer wood (fig. 38). 



III. Diffuse-porous woods. — Pores numerous, usually not plainly visible on cross 

 section without magnifier. Annual rings distinct by a fine line of denser summer 

 wood cells, often quite indistinct; pores scattered through annual ring, no zone of 

 collected pores in spring wood (fig. 39). 



Note. — The above described three groups are exogenous, i. e., they grow by add- 

 ing annually wood on their circumference. A fourth group is formed by the endog- 

 enous woods, like yuccas and palms, which do not grow by such additions. 



I. — NON-POROUS WOODS. 



(Includes all coniferous woods.) 



A. Resin ducts wanting. 1 



1. No distinct heartwood. 



a. Color effect yellowish white; summer wood darker yellowish (under 

 microscope pith ray without tracheids) (Nos. 9-13) Firs. 



b. Color effect reddish (roseate) (under microscope pith ray with tracheids), 



(Nos. 14 and 15) Hemlock. 



2. Heartwood present, color decidedly different in kind from sapwood. 



a. Heartwood light orange red; 'sapwood, pale lemon; wood, heavy and 

 hard (No. 38) Yew. 



ADDITIONAL NOTES FOR DISTINCTIONS IN THE GROUP. 



Spruce is hardly distinguishable from fir, except by the existence of the resin 

 ducts, and microscopically by the presence of tracheids in the medullary rays. 

 Spruce may also be confounded with soft pine, except for the heartwood color of the 

 latter and the larger, more frequent, and more readily visible resin ducts. 



In the lumber yard, hemlock is usually recognized by color and the slivery char- 

 acter of its surface. Western hemlocks partake of this last character to a less degree 



Microscopically the white pine can be distinguished by having usually only one 

 large pit, while spruce shows three to five very small pits in the parenchyma cells 

 of the pith ray communicating with the tracheid. 



The distinction of the pines is possible only by microscopic examination. The 

 following distinctive features may assist in recognizing, when in the log or lumbei 

 pile, those usually found in the market: 



The light, straw color, combined with great lightness and softness, distinguishes 

 the white pines (white pine and sugar pine) from the hard pines (all others in the 

 market), which may also be recognized by the gradual change of spring wood into 

 summer wood. This change in hard pines is abrupt, making the summer wood 

 appear as a sharply defined and more or less broad band. 



' To discover the resin ducts a very smooth surface is necessary, since resin ducts are frequently 

 seen only with difficulty, appearing on the cross section as fine whiter or darker spots normally scat- 

 tered singly, rarely in groups, usually in the summer wood of the annual ring. They are often much 

 more easily seen on radial, and still more so on tangential sections, appearing there as fine lines or 

 dots of open structure of different color or as indentations or pin scratches in a longitudinal direction. 

 64 



