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. Hard woods. Most 
a.r 
of the hard wood used for 
all kinds of construction 
in 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 . 
a.r, boundaries between one year’s growth, 
half of our supply of or annual ring, and the next. The large, 
hard-wood timber. Tulip- roundish white spots are resin passages that 
Pp have been cut off. Magnified 15 diameters. 
wood, or yellow poplar Photomicrograph by R. B. Hough 1 
(Liriodendron), is used in 
great quantities for the interior finish of houses and in the 
manufacture of woodenware. 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 
Lamar he 
a 
a) 
Fig. 91. Cross section of white pine, a 
typical coniferous wood 
1 From “ Handbook of the Trees of the Northern States and Canada,” 
written and published by Romeyn B. Hough, Lowville, New York. 
