101 



This change in size occurs across the grain of the wood, or across the cells of 

 which it is composed, and only to a slight degree in the direction of their length. 



Some pieces of unseasoned jjoplar had iron bars ten inches long placed be- 

 tween the projecting ends to prevent the ends coming any nearer together, and 

 were then allowed to remain in the conditions of ordinary workshop atmosphere 

 until they broke, which they did in the average time of four hours after adjust- 

 ment. 



A number of tests made in a testing machine showed that a force of about 

 370 pounds to the square inch was required to break them. 



Trials made with other wood gave corresponding results; in a few hours each 

 piece broke, the force required to break it depending on the kind of wood. In 

 some cases the force was over 600 pounds to the square inch. 



A microscopic examination of sections made from some of the pieces after 

 they had been allowed to dry, showed, first, a loss of the contained moisture, and, 

 as the drying continued, in some cases what seemed a shriveling of the tissues of 

 the side walls. 



An examination, previously made, of tlie cell walls of some wood that had 

 been in a dry place during some years showed a disintegration of the tissue, the 

 cell walls having a rough and fibrous appearance. 



In order to record any microscopic change taking place in tlic cell walls, two 

 sections, one a transverse and the other a longitudinal radial one, were made from 

 a freshly cut branch of Pinus ■■<ylvestris and mounted dry under cover glasses. 

 They were photographed at intervals and records made of changes occurring in 

 tliem. The moisture Hrst dried out, the cells in transverse section becoming 

 slightly less in size. After a few days when the moisture had dried from between 

 the walls, the greater change seemed to take place in the longitudinal section, the 

 walls of which began to shrivel slightly. This change continued for some weeks 

 in a constantlv lessening degree, however. 



