314 PLANTS AND MAN 



doors, sash, and interior trim. The remainder is manufactured 

 into boxes, crates, furniture, vehicles, and railway cars. 



Cross ties. — ^The amount of wood used annually for railroad 

 ties is exceeded only by that used for lumber and fuel wood. In 

 normal years as many as seventy five million cross ties have been 

 used, but this amount has been lowered recently, due partly to 

 the increasing use of preservative treated ties which need replac- 

 ing less often than the previously untreated ones. In the latter 

 condition a normal life of five to eight years could be expected; 

 treated, they serve twenty to thirty years. Most of the cross ties 

 used in the United States are of oak, southern pine, and Douglas 

 fir. Other species used to a much lesser extent include redwood, 

 western red cedar, cypress, tamarack, western larch, western and 

 eastern hemlock, lodgepole pine, red and tupelo gums, beech and 

 maples. 



Hewed ties are cut from felled trees in the woods, being faced 

 on two sides with an axe. There is consequently a greater varia- 

 tion in size, depending upon size of trees, than in sawed ties. 

 For this reason, and because slabs from the latter may be used for 

 manufacture of other products (whereas the chips from hewed ties 4 

 are waste) and the greater ease of treating sawed ties with pre- " 

 servatives, there has been an increasing production of the sawed 



type. . . I 



Poles and piling. — Our electric light and power transmission ' 

 lines, and telephone and telegraph systems of communication 

 normally require about three million poles per year for replace- 

 ments and new installations. This represents an annual expendi- 1 

 ture of about $10,000,000. I 



Chestnut was formerly one of the most important species used 

 for this purpose, but it is steadily decreasing in importance 

 because of its susceptibility to the chestnut blight (see p. 424). 

 The cedars, including western red, northern white, and southern 

 white, are all important pole species, since their woods are very 

 durable even in an untreated condition. Southern pine is ex- 

 tensively used in the treated condition, having an estimated life 

 of forty years. In the Eastern United States, about three-fourths 

 of all poles used are supplied by the southern pines. The most 

 common sizes of poles are from sixteen feet with four inch tops 



