CHAPTER XXII 



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TIMBER: FORESTRY 



361 . Coniferous woods. Our native woods 1 are best classified 

 into the two principal groups of soft (or coniferous) and hard 

 woods. 2 The needle-leaved or coniferous trees of the country fur- 

 nish more than three quar- 

 ters of our timber supply. 

 The structure of conif- 

 erous wood, as seen for ex- 

 ample on the end of a beam 

 cut off squarely, or on a 

 new lead pencil, is in one 

 respect less complex than 

 that of most hard woods : 

 the wood is chiefly com- 

 posed of tracheids, long 

 tubular cells with taper- 

 ing ends, and contains no 

 continuous ducts (it may 

 contain resin passages). 

 The rings plainly seen on 

 the cross section of some 

 kinds are due to the dif- 

 ference in diameter of the 



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FIG. 316. Cross section of typical conif- 

 erous wood of white pine 



a.r, boundaries between one year's growth, 

 or "annual ring," and the next; the large, 

 roundish white spots are cut-off resin pas- 

 sages. Magnified fifteen diameters. Photo- 

 micrograph by R. B. Hough 3 



tracheids formed in early 

 spring and later (Fig. 316). 



1 "Timber," Bulletin 10, Division of Forestry, U.S. Dept. Agr., 1895. 



2 Some of the needle-leaved or coniferous trees, such as the larch and the 

 yew, have rather hard wood; and some broad-leaved trees, such as willows, 

 poplars, tulip trees, and buckeyes, have soft wood; but people who deal in 

 timber usually speak of the two general classes as explained above. 



3 From Handbook of the Trees of the Northern States and Canada, writ- 

 ten and published by Romeyn B. Hough, Lowville, New York. 



390 



