72 



ing treatment, became insufficient to meet the needs of the roads. No 

 sap ties possessed this quality, and small timber, even of the desired 

 species, would show too large a proportion of sap to class as "U" ties. 

 The roads met this situation, not by substitution but by timber preserva- 

 tion, which enabled them to draw upon a large reser\-oir of timber of 

 species not sufficiently resistant to decay to have been formerly acceptable. 

 Instead of being confined to white oaks, black locust, walnut, pine, cedar, 

 cypress, catalpa, chestnut, mulberry, and sassafras, and mainly heart- 

 wood, the sap ties of all these species, and in addition many new species 

 could now be used. Of these the most important is the red or black 

 oak group, which grows nearly twice as rapidly as the white oak group. 

 Others are the ashes and hickories, honey locust, beech, formerly a wood 

 in little demand in most regions, birches, including the paper birch which 

 formerly was permitted to burn after pine lands were logged, cherries, 

 gums, which constitute an enormous quantity of timber in the South, 

 hard maple, one of the most numerous species in the northern woods, 

 elms, hackberry, soft maple, sycamore, and butternut. Practically the 

 only trees remaining which are unsuitable for ties are such species as 

 Cottonwood, tulip-poplar, and basswood, which are too weak to with- 

 stand mechanical stress, and are more valuable for other purposes. The 

 expansion of the field of utilization and market for cross-ties to cover 

 practically every species not otherwise valuable found in the wood-lots 

 and forests of Illinois, is one of the most significant and encouraging 

 phenomena of recent years, and is a striking proof of the fact that timber 

 crops, when grown to merchantable sizes, regardless of the species which 

 compose the stand, will in the future find a ready market unless the 

 national neglect of forest production reaches such colossal projiortions 

 that entire industries are dislocated and forced to resort to substitutes. 

 Even should such shifts occur through necessity, wood will regain its 

 place at any future time when it is produced in sufficient quantities to 

 furnish a dependable source of supply. 



The effect of preservatives upon the life of ties of different species 

 is to establish an average .service of from 15 to 16 years per tie including 

 those species formerly rejected, as against about 10 years for the formerly 

 accepted durable species, and 2 to 5 years for the unserviceable kinds. 

 The relative durability is affected by several factors. Very durable 

 woods, such as white oak, do not show a corresponding increase in longev- 

 ity when treated. The greatest relative gain comes in treating such 

 woods as birch and maple which otherwise decay rapidly. 



