16 



TIM15ER PINES OF THE SOUTHERN UNITED STATES. 



Ill any one tree the wood is lighter and weaker as we pass from the base to the top. This is 

 true of everj- tree and of all four species. The decrease in weight and streiis'tli is most prououuced 

 in the first 20 feet from the stump and grows smaller upward. (See lig. 1.) 



49.6 



Feet frOTti Stump. 



This great difference in weight and strength between butt and top finds explanation in the 

 relative width of the summerwood. Since the specific weight of the dark summerwood band in 

 each ling is in thrifty growth fiom 0.90 to 1, while that of the siu'ingwood is only about 0.40, the 

 relative amount of summerwood furnishes altogether the most delicate and accurate measure of 

 these differences of weight as well as strength, and hence is the surest criterion for ocular iusi)ection 

 of quality, especially since this relation is free from the disturbing influence of both resin and 

 moisture contents of the wood, so conspicnous in weight determinations. 



The following figures show the distribution of the summerwood iu a single tree of Longleaf 

 Pine, as an examjjle of this relation: 



