DENSITY OF WOOD. 



145 



rather than upon the latter. The lightest wood is probably the 

 so-called " cork- wood" of the West indies (Ochromu Lagopus), 

 with a specific gravity of .25 ; the heaviest is Condalia ferrea, 

 specific gravity 1.302. 1 The specific gravity of pure cellulose is 

 given by authors variously as 1.25 to 1.52 ; 2 hence the figures 

 noted above for the extremes of wood-density show indirectly the 

 degree of buo3*ancy imparted by the air entangled in the tissues. 3 

 412. Wood-fibre used for paper-pulp. The longer wood-cells 

 of many common ligneous plants can be profitably separated 



1 Tenth Census of the United States, vol. ix., p. 272. 



2 Ebermayer : Chemie der Pflanzen, 1882, p. 164. Husemann and Hilger: 

 Die Pflanzenstoffe, 1882, p. 108. 



8 The following determinations were made under the direction of Professor 

 C. S. Sargent, for the Tenth United States Census. 



The specimens used in the above determinations by Mr. S. P. Sharpies were 

 dried at a temperature of 100 C. until they ceased to lose weight, when the 

 specific gravities were obtained by measurement with micrometer calipers and 

 calculation from the weights of the specimens. 



For the purpose of utilizing histological features in the identification of 

 woods, classiticatory tables have been prepared by many authors. One of the 

 most useful of these is given in Schacht's work, Die Pflanzenzelle, in which 

 the different wood-cells of Conifene are described, in order to aid in the recog- 

 nition of the genera. Another is de Bary's ( Vergleichende Anatomie. p. 509, 

 10 



