r887.] NEW-YORK MICROSCOPICAL SOCIETY. 33 



Beside the visible resinous matter in the cells mentioned, 

 tests indicate that in the duramen there is resinous matter on 

 and in the walls of the ordinary tracheids. They do not absorb 

 or imbibe water readily or in sufficient quantities to cause the 

 wood to become "water-logged" after being submerged many 

 years. 



The delicate middle lamellae can be traced in the lenticular 

 markings so there is not a free and unbroken communication 

 between the tracheids, water being prevented from passing 

 freely from cell to cell. 



The thinness of the cell walls in this wood gives a greater per- 

 centage of weight, of the middle lamellae, to the whole weight 

 than in some other woods, and this may help account for a 

 portion of its non-absorbing properties. 



The physical properties of the tracheids as regards strength are 

 not proportionally as great according to their specific gravity as 

 those of many others of the coniferous woods, it having but few 

 of the fibres per layer which contribute most of the strength 

 and elasticity to a wood. 



The data were compiled from a series of tests upon woods made 

 upon the U. S. Testing Machine at the Watertown Arsenal. The 

 specific gravities and crushing strengths are the average of 4 to 

 8 specimens of each wood. 



The ratio means the number of pounds per square inch re- 

 quired to crush the wood, provided the specific gravity was i. 

 The specific gravity of pure cellulose has not been determined, 

 but is estimated to be from 1.25 to 1.45. The relatively low 

 crushing resistance of the white cedar, according to its specific 

 gravity, is very marked, in comparison with the other woods 

 given in the table, and has given rise to the hypothesis, that there 

 is a difference in the chemical composition between the thick 

 and the thin walled tracheids. I had a series of chemical an- 

 alyses made to determine the matter if possible. A slight differ- 



