I9I9] 



HENDRICKS— TORSION 



433 



the corresponding values in the rigidity curve. This demonstrates 

 that increase in diameter accounts to a great extent for increase in 

 rigidity during most of the internode's growth, but does not at all 

 account for the final increase in rigidity. 



Many experiments were performed under somewhat different 

 conditions. The results of a few of these are presented graphically 



Fig. 6 



on a smaller scale in fig. 6, while some of the important data are 

 given for purposes of comparison in table II. The curves of twist, 

 rigidity, and coefficient of rigidity show the same characteristics 

 as those already outlined for fig. 5. It should be mentioned, how- 

 ever, that the final drops in the twist curves in fig. 6 have necessarily 

 teen more or less exaggerated. Curves D-1 and D-ll are for 

 black bindweed, where the torsion is in the opposite direction from 

 that in the flowering bean, being in the same sense as the thread 



