TIMBER; FORESTRY 



109 



The structure of coniferous wood as seen, for example, 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 composed of tracheids long, tubular cells 

 with tapering ends and contains no continuous ducts, though 

 it may contain resin pas- 

 sages. The rings plainly 

 seen on the cross sections 

 of some kinds are due to 

 the difference in diameter 

 between the tracheids 

 formed in early spring and 

 the later ones (fig. 91). 



103. Hardwoods. Most 

 of the hard wood used for 

 all kinds of construction 

 iii this country is fur- 

 nished by native trees. 

 Of these we have about 

 eighty kinds, the most im- 

 portant ones being the oaks 

 (of about nineteen species). 

 These furnish more than 

 half of our supply of 

 hard-wood timber. Tulip- 

 wood, or yellow poplar 

 (Liriodendrori), is used in 

 great quantities for the interior finish of houses and in the 

 manufacture of wooden ware. The wood is soft, free from 

 knots, and furnishes very wide boards. It is not durable when 

 exposed to the weather. 



Other important hard woods are ash, beech, birch, chestnut, 

 elm, maple, red gum, and sycamore. Each of these woods has 

 its valuable qualities and its defects, well known to builders 



1 From " Handbook of the Trees of the Northern States and Canada," 

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



FIG. 91. Cross section of white pine, a 

 typical coniferous wood 



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

 or annual ring, and the next. The large, 

 roundish white spots are resin passages that 

 have been cut off. Magnified 15 diameters. 

 Photomicrograph by R. B. Hough 1 



